bài giảng xạ trị

8/21/2019 bi ging x tr

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Bi Ging Vt L Ht Nhn ng Dng

Cn Bn Viu Tr

Bng Liu Php Bc X


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Mc LcTng Quan Viu TrXTr ............................................................................................. 1

I. iu tr b ng tia x l g ? ............................................................................................. 1II. Cc Phng thc iu tr trong x tr : .......................................................................... 1

III. Cs v t l trong iu trx tr :................................................................................... 1IV. Khoa iu Tr B ng Bc X: ....................................................................................... 1V. i Ng Nhn Vin T i Khoa XTr :.......................................................................... 2VI. HTh ng Thit BC a Mt Khoa X Tr :................................................................... 4VII. Quy Trnh iu TrT i Khoa XTr ............................................................................ 4

HThng Trang Thit BTrong n Viu TrBng Tia X ........................................ 5I. Tng quan vh th ng trang thit bc a n v iu tr: ............................................. 5II. Thit B iu Tr:.......................................................................................................... 6III. HTh ng Thit BHng nh: ....................................................................................... 7IV. HTh ng Lp KHo ch iu Tr: .............................................................................. 7V. Hth ng m phng v kim tra.................................................................................... 8

VI. Hth ng Phng Mould room: ...................................................................................... 8VII. HThi t B o Liu v QA-QC:.................................................................................. 9VIII. Tng Quan VMy iu Tr Gia T c Tuyn Tnh:..................................................... 9

Vai Tr Ngi Vt L v Cng Tc Vt L Trong iu TrXTr ............................... 17I. Nh Vt L XTr : ..................................................................................................... 17II. Vai Tr Ca Nh Vt L Y Khoa: .............................................................................. 17III. TCh c i NgV t L Y Khoa Trong Mt Trung Tm X:.................................. 17IV. Cng Tc Vt L Trong X Tr : ................................................................................. 18V. TCh c Nhn SV Cng Tc V t L:.................................................................... 20

Nhng Vn Vt L CBn Trong XTr Cc Thng SVt L CBn ............... 21I. Cc Loi Bc X Pht Ra T my Gia t c c sd ng trong xtr : ...................... 21

II. Bia Tia X Trong My Gia Tc Tuyn Tnh................................................................ 21III. Ph N ng Lng Chm Photon:................................................................................ 23IV. n VN ng Lng Ca Cc Chm Tia Bc XTrong X Tr :............................... 23V. SPhn B N ng Lng Ca Chm Bc XV i Mi Trng - SCn B ng

Electron:...................................................................................................................... 24VI. Chm Tia Bc XV Tr ng Chiu:......................................................................... 26VII. Beam Profile V Penumbra: ....................................................................................... 27VIII. S ng u Ca Trng :........................................................................................ 30

Nhng Thng SVt L CBn Trong Tnh Ton Liu ................................................. 32I. Gii Thiu:.................................................................................................................. 32II. Hs l ch trc OAF: .................................................................................................. 32III. Hs Output: .............................................................................................................. 32IV. Phn Trm Liu Su (PDD):............................................................................... 34V. SPhn B ng Liu: .............................................................................................. 35VI. Thng SC a Chm Tia Nng Lng Cao TMR v TPR:........................................ 37VII. Cc hs tnh li u khc: ............................................................................................. 39


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Tng Quan Viu TrXTr

I.iu trbng tia xl g ?

iu trbng tia bc xhay cn gi tt l XTr l vic p dng cc ngun bc xht nhn hay cc chm tia bc xvo vic iu trbnh trong y hc ni chung, iu trbnhnhn ung thni ring.

Vic p dng bc x h t nhn trong y hc nh v y c thc hin t r t sm ngay t nh ngngy u tin khi tia X c pht hin ra bi nh vt l Roentgen v sau ba khm ph quantrng: Tia X bi Roentgen; Sb c x t nhin b i Becquerel v Ra-226 bi Marie Curie. Ccloi bc x c p dng trong iu tr trong nh ng ngy u l nhng chm tia X c nnglng thp, tuy nhin ngy nay chng ta c nhiu la chn a dng hn nh chm tia X n nglng thp, chm tia X nng lng cao hay cn gi l chm photon hay tia gamma, chm tiaelectron hay cc chm ht nng nhproton, He, Cacbon c ng bt u c s d ng m t s nc tin tin trn thgi i nhng gi thnh kh cao.

Cc chm tia bc x ny c pht ra tcc my pht hay nh ng ngun ng v phng x ch nghn nhmy gia t c tuyn tnh, my gia tc vng hoc ngun ng vCo-60, ngu n Ir, Ra.

II.Cc Phng thc iu trtrong xtr:Xtr c chia lm hai phng thc iu tr l x tr trong v x tr ngoi.

X tr trong l vi c a cc cht ng v phng x vo bn trong vng c n iu trv t i cc chm tia bc x c pht ra cc hng xung quanh tiu di t t bo ung th xungquanh.

X tr ngoi hay x tr t xa l vi c sd ng cc my pht hay cc ngun ng vb c xt

bn ngoi bnh nhn c nh hng chiu vo cc khi u bn trong bnh nhn. Vi xtr ngoi hng chiu hay ng i ca cc chm bc x c n c xc nh khi lp k hochiu tr cho b nh nhn. Cc my pht bc x trong x tr ngoi tu theo n ng lng chm tiav mc ch sd ng m c ch t o khc nhau. iu trcho ung th b m t da thngthng l cc my tia X nng lng thp hay cc ngun ng v phng x n ng lng thp,cho nhng khi u nm su hn bn di bm t da ca bnh nhn cc my pht tia X nnglng cao c p dng: trc y cc my Co-60 nng lng 1.33 MeV c sd ng khphbi n, nhng vi thp nin gn y cc my gia tc tuyn tnh vi nhiu mc nng lngkhc nhau t 4 MV, 5 MV, 6MV, 10 MV n nng lng rt cao hn 21 MV v c thphtc cc chm b c x electron ang c sd ng kh phbi n. My gia tc tuyn tnh ngynay do nhng u im hn hn my Co-60 cho thy nhng u vit ca n.

III.Csvt l trong iu trxtr:

IV.Khoa iu TrBng Bc X:

Khoa iu trbng bc xhay khoa x tr l mt n vkhm v iu tr cc bnhc chnh sdng cc loi tia bc xtrong iu trbnh, chyu l cc bnh nhn ungth. Tu theo c c u tch c t t ng nc, tng thnh ph v t ng bnh vin m mt n vx tr c th l m t trung tm hay khoa x tr c lp ca mt bnh vin, hoc l mt n v tr cthuc mt khoa ca bnh vin v cc hnh thc tch c khc.

Khoa iu trbng bc xthc hin iu trbnh nhn da trn cc thit bc bit

cho cng tc ca n nh: cc my pht bc x, cc h th ng my tnh iu khin v lp khoch cho vic iu tr, cc thit bph tr c bit c yu cu cho vic iu tr.

Bi Ging vt L XTr_ Trn Cng 1


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V v y khoa x tr yu c u c mt s lin k t, hp tc gia nhng nhn vin m nhntrch nhim vy khoa, v thi t b v v v t l.

V.i NgNhn Vin Ti Khoa XTr:

i NgNhn Vin: - Nh Ung B u Hc bc x.

-

i ngv t l xtr .- i ngk thu t vin.- i ng iu dng, y t v nhn vin vn phng.

Trong :

Mi nhm nhn vin ny c chc nng v nhim v khc nhau trong m i lin hr ng buc cacng tc xtr nh c minh ho trong s sau:

BS XTr

Khm v Ch nh

iu Dng &Nhn Vin Vn

Vt L KThu t Vin

Lp KHT Thc hin mphng

nh gi KHT

QA & QC thit b Thc hin iu tr

Theo Di-ng Gi

Trin Khai KT mi Thc hin QA n gin

Trin Khai Pm i

Nghin cu ng gp vKT m i

Gip BS lp HST

Cng tc VP & BHYT

Qun l Bnh n

Kt qu T

S M u VT Ch c Khoa XTr



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Lch T & TD

Phng Khm

DLi u MP

Server

HT. LKH

Hnh Anh Hc

P. M Phng My Linac

Lp KHT

P. Nhn Bnh HT. Thng Tin

TT. Bnh n

TD. Ti Khm

Phim MP DLi u chm Tia

TT iu Tr

TT. Bnh Nhn

Vin Ph

Qun L HS BN

Qun L NV & TB

CT, MRI, PET

Khu X Tr

Khu Ho Tr

Phc & Li u Lng

Qun L Bit Dc

S HThng Mng V D Ca Mt Khoa Ung Bu

Nh Ung Bu Hc bc x:c trch nhi m trong vic khm v ra quyt nh iu tr. Hsquy t nh vph ng thc iu tr, ch nh liu lng v theo di bnh nhn.

i ngKSVt L xtr: c trch nhi m trong vic m bo cht lng thit b, lp k hoch iu tr ( nh hng n cht lng ca t iu tr trn b nh nhn). H a ra kthut iu tr d a trn nhng ch nh ca cc nh Ung Bu hc bc x v m bo chtlng ca vic iu trtheo ng kthu t a ra.

i ngKThut Vin: y l i ngc m i lin h m t thit, cht chgi a cc nh UngBu hc, i ngK S v t l v bnh nhn. Hc trch nhi m trong vic thc hin kthut iu tr c a ra, nhng yu cu ca vic iu tr t c kt qu iu tr mong mun. Hl i ng tr c tip thc hin vic iu tr, hh tr th c hin cc k thu tiu trv l ng i c nhiu ng gp trong vic nh gi v hon thin cc kthu t iutr ang p dng. Cng vic ca h nh hng trc tip n cht lng iu tr v n l ciu tr c a c m t quy trnh iu tr.



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iu dng, Y t v Nhn vin vn phng: l i ng ti p nhn v gii quyt th t c chobnh nhn, gip h tr bc strong khm b nh v hon tt h s b nh n. Vi trnh chuyn mn cao hn h c th m nhim trong vic qun l v lu trh s .

VI.HThng Thit BCa Mt Khoa XTr:

HThng Thit B: - Thit bh tr khm b nh.- H th ng mng lu trv trao i thng tin .- H thi t bh tr iu tr.- H thi t bhnh nh, My CT cho mc ch iu tr.- My m phng.- H th ng lp kho ch.- My iu tr.- H th ng thit bki m tra

VII.Quy Trnh iu TrTi Khoa XTr

Qui trnh ieu tr la s khai quat cac bc cua mot t ieu tr ma ngi benh phai iqua. Qui trnh ieu tr noi nen s logic ve to chc va noi len nhiem vu, trach nhiem cac nhomnhan vien tham gia vao cong tac ieu tr bang bc xa. Co the khai quat qui trnh ieu tr xatr bang s o sau:

T s o tren cho thay mot quy trnh ieu tr xa tr hoan chnh la mot quy trnh phctap gom nhieu bc, nhieu khau co moi quan he khang kht vi nhau cau thanh nen. Tai moiv tr, moi khau o vai tro va trach nhiem cua moi nhom nhan vien la khac nhau, nhng comoi quan he qua lai tng ho lan nhau.



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HThng Trang Thit BTrong n Viu TrBng Tia X

I.Tng quan vhthng trang thit bca n viu tr:Cc thit b c a mt khoa x tr c gii thiu sl c trong phn trc, tuy nhin mt

cch tng quan cc thit b ch y u ca mt n vx tr s bao g m:

Thit b iu tr.

Thit bch n on

Hth ng lp k ho ch

My m phng v hth ng thit bki m tra

Hth ng phng muold room

Hthi t b o liu v QA-QC

Trong :Thit biu tr:

Thit b x tr ngoi: My iu trb m t X-quang sut liu cao My Co_60 My gia tc tuyn tnh My gia tc ht nng

Thit b x tr trong: Kim phng xv Implane My sut liu thp LDR

My sut liu cao HDRThit bchn on:

my chp X-Quang, CRmy siu mmy CT ct lpmy DSAmy MRImy SPECmy PET hoc PET/CT

Hthng lp khoch:

Lp k ho ch iu tr x trongLp k ho ch n gin 2DLp k ho ch conformal 3DLp k ho ch IMRT IGRTLp k ho ch Radiosurgery.

My m phng - Hthng thit bkim tra:My m phng.My CT-m phngThit B ch p Port Film, CR, DRH th ng EPID

HThng thit bphng Mould room:My ct block cho electron v photon



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Ni nu hp kim to block che chnDng cc kh, khoan, my phay v thi t b khc

Hthit bo liu v QA-QC:H Phantom n c.H th ng qut trong khng kh

Phantom rn tng ng nc.Phantom c bit (la chn)Bung Ion ha cho chm photon.Bung ion ha cho chm tia electron.Nhit k.p sut kElectrometerThit b ki m tra n nh ca bung ion haThit b ki m tra n nh ca Electrometer.Phim chp kim tra.H th ng qut mt phim. (densitometer)

H th ng o liu trn bnh nhn (TLD v Diodes).Thit b ki m tra Laser v Isocenter.Phantom cho CT v chun phn mm lp kho ch.Electrometer cho vic kim tra kV v mA cho my tia X.Cc thit bt lm n u c.

II.Thit Biu Tr:II.1.My ii trbmt

My iu trb m t c cht o v p dng cho nhng trng hp ung thda c xmln t. My iu trb m t l nhng my X-quang sut liu cao c cc bcollimator t ng ng vicc vng din tch iu tr.

II.2.my Co-60:

My Co-60 l thit b iu tr s d ng ngun bc xnng lng cao 1.33 MeV c phtra tngu n ng vphng x Co-60 chi u vo cc khi bu bn tronh bnh nhn. My Co-60 ngy nay c thit k c ng rt gn v c hnh dng ging vi cc my gia tc tuyn tnh.

II.3.Cc thit bng dng gia tc tuyn tnh:

Cc My iu trx tr ng dng gia tc tuyn tnh l cc thit b iu tr hi n i da trnsgia t c tuyn tnh cc ht electron trong mi tr ng in t tr ng v to ra chm tia photonbng cch cho chm tia electron bn vo mt bia tia X. Cc my ny c thto ra c cc mcnng lng khc nhauc a chm tia iu trph h p hn trong vic iu tr cc tn thng cc

vtr su. My gia tc tuyn tnh cho php la chn hoc chm tia photon hoc chm tia electron



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iu tr tr c tip cho bnh nhn. Cc phng php v k thu t iu tr b ng my gia tc angngy cng pht trin v em li hiu qucao.

1. Cc c tnh ca cc my ng dng sgia t c tuyn tnh- C thl a chn hai loi chm tia bc xPhoton v Electron.- C nhiu mc nng lng khc nhau ca hai loi chm tia bc xphoton v electron.

-

an ton b c x cao. - chnh xc v li u lng v chuyn ng ckh chnh xc. - C nhiu sl a chn vc u hnh v tnh nng- p dng cc kthu t iu trhi n i khc nhau.

2. Cc loi my p dng gia tc tuyn tnh hin nay:- My gia tc tuyn tnh Linac: Siemens, Varian, Elekta- My Cyber Knife- My Tomotherapy- My iu trb ng ht nng

II.4.My xtrtrong:

iu tr x tr trong l iu tr cc tn thng hoc cc khi ung thbng cch a ccngun ng vphng xvo pha bn trong vng tn thng hay khi but pht tia bcxph h y khi bu. iu trx trong theo t ti ng anh l Brachytherapy tc l iu trp st,iu ny cn c ngha l cc ngun ng v phng x tip xc, p st vo khi bu. Cc hthng ng dng trong iu tr x trong bao g m

Kim phng x v Implane My sut liu thp LDR My sut liu cao HDR

III.HThng Thit BHng nh:

Thit bhnh nh hc trong h th ng trang thit b iu trx tr c vai tr r t quan trng.Cc thit bny m nhim hai chc nng chnh: Chc nng chn on hnh nh v chc nngthu thp d liu u vo cho h thng lp khoch iu tr.Cc d li u hnh nh t cc lo ihnh nh khc nhau c th c s d ng kt hp li hin thhnh nh tn thng tt nht.Trong n v iu trx tr nn c t nh t mt my CT, my CR v my siu m, cc thit bkhcc thk t ni vi khoa chn on hnh nh nhPET/CT, SPEC, MRI ...

IV.HThng Lp KHoch iu Tr:

Hthng lp khoch l mt hthng bao gm my tnh v phn mm dng cho cngvic m phng iu trv tnh ton liu lng, thng sci t my theo m hnh btr nhtrong m phng. Hth ng lp kho ch ss d ng cc dli u hnh nh nh nh CT, MRI, PET,DSA sau s k t hp vi m hnh h a iu tr v cc thu t ton tnh liu tnh ton s phn bli u ti u cho vic iu tr. Trn thtr ng hin nay c nhiu hng cung cp hth ng lp



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kho ch khc nhau vi nhng thut ton tnh ton liu v vi nhng kthu t iu tr kh ph c tp.Vi t Nam cng vic lp kho ch l mt trch nhim ca ngi Vt L Y Khoa.

Cc h th ng lp kho ch hin nay bao gm cc phn:

Lp k ho ch iu trx trong

Lp k ho ch iu tr2D

Lp k ho ch iu tr3D Lp k ho ch iu trk thu t IMRT - IGRT

Lp k ho ch Radiosurgery

V.Hthng m phng v kim tra.

Hthng my m phng bao gm my m phng v hthng my tnh iu khin mym phng cng nhlu trv sl dliu m phng.H th ng my m phng ch i km vimy iu trCo-60 v my gia t c tuyn tnh cc my iu trkhc c th khng s d ng n mym phng, hthng my m phng l mt my soi X-quang c cc tnh nng v m hng gingnhmy iu trgia tc tuyn tnh hay my Co-60. chc nng ca my m phng l kim travic iu tr v vi c che chn c to ra th th ng lp kho ch trc khi a bnh nhn iu trchnh thc trn my iu tr. Cc th h my m ph ng khc nhau c cc tnh nng pht trin khcnhau nhch c nng CT chng hn

VI.Hthng Phng Mould room:

L phng c sdng thc hin cng vic to cc mt n, cc khun cnh cho

bnh nhn, phng mould room cng l phng to cc khi che chn, cc dng cckh



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phng ny cng c trang b cc h th ng nh v nh trong phng m ph ng, v cn cxem nh m t workshop.

VII.HThit Bo Liu v QA-QC:

QA-QC l hth ng khng ththiutrong m t trung tm iutr b ng

Hth ng thit b o liu vbc x v l cng c chnh c a cc k s v t l thc hin cc cng tc lin quan n

cc php o c liu lng v cng tc bo m cht lng ca chm tia bc x cng nhchnh xc, tin cy c a hth ng thit b iu tr. y l h th ng thit bquan tr ng i vi ccnh vt l. Cc thit bc n thit ca hth ng o liu n cn bn c lit k nh ph n trn.

VIII.Tng Quan VMy iu TrGia Tc Tuyn Tnh:VIII.1. Gii Thiu VMy Gia Tc:



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VIII.2. Cc Thnh Phn Chnh Ca My Gia Tc Tuyn Tnh:

t t r t nhiu chi tit khc

ra.

Cu rc my gia tc tuyn tnh trong iu tr x tr c to nnnhau, tuy nhin mt cch tng quan ta c thchia lm 6 ph n chnh:

- Phn thn my ng yn.- Thn quay ca my hay Gantry

-

u my hay Collimaytor- Bn iu Tr.n my- Phn iu Khi

- Thit bghi hnh ki m t

Vm t chi ti t cc phn cu to ch y u cn ch bao gm:

h.

in liu lng.

ollimator chun.

im tra EPID

- bpht sng cao t n RF- Sng pht electron.- ng gia tc.

uyn tn- ng gia tc t- Bb chm tia.-

Bia tia X.iu kh- Chamber

- Blm ph ng chm tia.u hay C- B nh dng trng chi

- B nh dng trng chiu nhiu l MLC- Hth ng quang hc.- Bn iu tr

n- Hth ng iu khi- Hth ng nh vv k



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VIII.3. Nguyn L Hot ng Ca My Gia Tc Tuyn Tnh:

y tc cc chm tia electronNgu n tc hot ng ca my gia tc tuyn tnh da trn sgiapht ra tm t sng bn electron, cc chm electron ny c gia tc trong mt trng in tcaotn c pht tb pht sng cao t n trong mt ng gia tc thng. cc chm electron ny c gia

tc ti vn tc gn bng vn tc nh sng sau cc chm tia ny c chiu theo hng li raca my s d ng iu tr cho b nh nhn, hoc c hng bn vo mt bia kim loi t o rachm tia photon iu trcho b nh nhn.

VIII.4. Mt SKhi Nim khi sdng my gia tc trong iu trung th:



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1 Isocenter (Tm quay, Tm chiu x): L mt im trong khng gian. cch bia tia X100cm v l giao im ca 2 trc i xng: Trc i xng ca chm tia X pht ra tbia tia X v trc quay i xng ca gantry

2.

Gantry: L phn thn my c th quay c 360

0

quanh m t tm quay, b ng giatc v nhiu thit bkhc u nm trn Gantry. Cc chm tia bc x c ng c phtra tm t vtr trn Gantry v ty vo v tr gc c a Gantry, cc chm tia schi u vobnh nhn theo cc hng khc nhau.

3. Collimator: L mt khi gm cc Jaws hay cn gi l cc ngm cu thnh nn ccoi l phn u my nm trn Gantry. Collimator v vy xc nh kch thc v gcquay ca cc chm tia bc x pht ra t ng gia tc. Nhgc quay c a Collimator mcc chm bc x c lm ph hp hn vi hnh dng khi bu.

4. Jaws: l cc kh i kim loi che chn sc p ca my tao ra m t kch thc v hnhdng chm tia bc x ph h p vi l n ca vng cn chiu v ng thi che chnvng khng cn chiu x. Cc jaws ny gm 4 ci xp theo hnh tng cp i xongvi nhau theo hnh ch nh t to thnh b g i l Collimator v c gn nm trnGantry

5. MLC: L mt Collimator thc cp nm pha di ca bCollimator s c p. BMLCc to nn bi nhiu l kim loi mng gp vi nhau theo tng cp i song gingnh 2 jaws c Collimator s c p. MLC gip to ra cc chm tia bc x ng theohnh dng v kch thc khi bu ti cc hng khc nhau ca Gantry.



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6. Trng Chiu X (Radiation Field): l chm tia bc x chi u vo vng tnthng vi hnh dng v kch thc c xc nh bi cc collimator s c p. kchthc trng chiu i vi cc my gia tc tuyn tnh l kch thc o c ti tmquay ca Gantry cch ngun 100cm

7.

Trng nh Sng (Light Field ): l chm tia nh sng m ph ng cho chmtia bc x. Trng anh snh c kch thc v hnh dng ging chm bc xpht ra vkch thc hnh dng trng nh sng cng c xc nh bi cc Collimator sc pv MLC thc p.

8. SAD: (Khong cch tngun ti isocenter): l khong cch tnh tbia tia X nIsocenter. Khong cch ny l 100cm i vi cc my gia tc tuyn tnh.

SSD (Khong cch ngun ti bmt da): l khong cch tnh tbia tia X n b

mt da ca bnh nhn.

9.



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10.ChThKhong Cch Bng Quang Hc (Range Finder):l m t b n chiu chin th cc thang chia chnh kho ng cch t bia tia X n v tr ang o. Thngdng o khong cch SSD.

11.Trays (Gi Khi Che Chn): L m t dng c b ng mica cc kh i chechn. i vi cc my gia tc c MLC th cc Tray ny khng cn c sd ng na.

12.Khi Che Chn (Block): L nhng khi c bng hp kim c tc dng dng che

ho ch vc gn ln cc Tray trong khi iu tr. Trong trng hp cc my gia tc c MLCs khng c n sd ng cc khi che chn na.

13.Port Film (Phim Chp Hnh Dng Trng Chiu X): L phim ch m hnh dng

v kch thc chm tia bc x chi u ra ti mt v tr gc no ca Gantry v gcquay no ca Collimator tng ng vi mt cha chn no hay mt sp xp no ca MLC. Hnh nh ca Port Film c lin quan n mc gii phu ca bnh nhnv l c s cho vi c so snh vi chm tia bc x trog l p k ho ch m bo siu trl chnh xc.

14.Headrest: l dng ch tr cho vi c iu tr. y l dng c dng u cabnh nhn trong mt tth iu trmong mu n. Dng c ny ty theo nh cung c pm c nhng cch btr v ki u dng khc nhau.

chn, bo v m lnh hay cc c quan tr ng yu nm gn khi u cn chiu x. cckhi che chn c hnh dng ty thuc vo thit k che ch n trong lp k



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15.Breast Board: C ng l mt dng c h tr trong iu tr nh Headrest, im khcbit l dng c ny c sd ng cho cc ca ung thv v vng ng c m thi.

16.Lung Board: l dng c h tr iu trgi ng nhBreast Board, nh ng y l dng

c c thit k c bit cho nhng ca ung thph i.

17.Themoplastic Mask:L m t dng cdng c nh cho bnh nhn. Loi dng cny lm bng nha thng minh c ththay i hnh dng khi nhit th p, v khi nhit quy nh chng s tr v hnh d ng ban u. Loi mt nny c nhi u loivi hnh dng v kch thc khc nhau cho tng vng ca c th nh u, bng vvng chu.



18/41

18.Bolus:l m t vt liu ging nhm ng i c tc dng b p phn m bthi u htt o ra nhng vng m bng phng hoc t ng bd y ca vng m c chiu xln t tng liu vng m gn b m t hay trn bm t ca da. Bolus c thit kthnh cc tp ln vi cc dy khc nhau cho cc m c ch sd ng khc nhau.

19. g hi u chnh sphn b li ulng ng u hn trong nhng trng hp vng chiu x khng ph ng v c Wedge (nm): l mt dng c lm b ng kim loi dn

cong no . Cc Wedge c thit kv i cc gc khc nhau ph h p vi cc gccong tng tng ca bm t chiu x. cc Wedge ny c chia lm nhiu loi tythuc theo vic chn mua thit bg m

Physical Wedge lm bng kim loi nm bn ngoi my c lm vo khi cn sdng

Dynamic Wedge: l Wedge bng kim loi nhng nm bn trong u my gia tc,khi sd ng s t ng c a vo vtr.

Vitrual Wedge: L Wedge khng c thc n c to ra bng cch hiu chnhcng chi u xd c theo mt hng no t to ra sthay i vs phnb li u ging nh cc wedge b ng kim loi. y l mt la chn (option) khi muamy gia tc.



19/41

V

I.Nh Vt L XTr:

Nh Vt L x tr hay ni chnh xc h n l cc nh Vt l y khoa, hl nhng nh Vtl c o to v chuyn mn ng dng Vt l ht nhn trong Y khoa bao gm kin thcVt l v kin thc vY khoa. Vx tr h c o to cc chuyn mn lin quan n cng tcx tr c a mt nh Vt l. Ti cc nc pht trin, ngi Vt l y khoa c o to theo mtchng trnh rt bi bn. n c ta hin nay, cha c trung tm hoc trng lp o to v chuyn nghnh ny.

II.Vai Tr Ca Nh Vt L Y Khoa:

Nh vt l y khoa ng mt vai tr khng nhtrong m t trung tm xtr . H m nhntrch nhim v cc cng tc V t l trong xtr . Nhim v chnh c a cc nh V t l y khoa trongx tr c th s l c nh sau:

m

Cung

Tv

m n ch nhim v m bo cht lng vic lp k ho ch iu tr.

nh gi chnh xc c a vic lp kho ch v kthu t iu tr.

Lp kho ch v thc hin iu trx .

Chun cc chm tia x ngoi v cc ngu n x trong.

Thu thp dli u cho cc thit b m i.

Cv n vk thu t v khoa hc trong lnh vc an ton bc x.

Cv n trong vic pht trin k thu t, pht trin v mua mi thit b.

Nghin cu v pht trin.

Trntrung tm xc th t ng tr cng v giao trch nhim c th khc

c th. Mt

III.TChc

V y l n thit trong mt trung tm x tr v i ng ny c m t vai tr khquan trng trong qu trnh hot ng ca khoa, v vy vic tch c mt i ngnh v y l cngvic cn c ch trng. Vic tch c bt c i ngnhn vin no u phthu c vo m hnht ch c v yu cu thc tc a cc trung tm. Tuy nhin y chng ta c thtrnh by m t cchchung nht vt ch c mt i ngnh ng nh vt l y khoa trong mt trung tm x nh sau. M ttrung tm x c t hai my gia t c (theo thc t t i vit nam) nn c ti thiu t5 ho c 6 nh vt

l y khoa vi vai tr nhsau:

ai Tr Ngi Vt L v Cng Tc VtL Trong iu TrXTr

m bo cht lng trang thit b.

nhim cng tc v o c liu lng.

cp gili u chm tia bc xa tcc my iu tr.

n trong iu tr b ng bc x

hn tr

y trnh by mt cch tng quan v nhi m vc a cc nh Vt l y khoa trong cctr. Tuy nhin trong thc t, tu theo m hnh t ch c, cc u tch c v iu kinung tm, cc nh Vt l y khoa s c phn

nhau trong m t mi lin h ch t ch m bo cc nhim v trn c hon thnh tt nht nhs nh ng nhim v ch y u trn s c c p chi tit cc ph n kti p.

i NgVt L Y Khoa Trong Mt Trung Tm X:

i ngc



20/41

Vt lu cu

ca n t a ra: cc quy trnh lm vic, nhng yu cu cng vic v nhng phncng hp l cng tc vt l n cc nh vt l khc, cng nh ra cc ph ng hng

t trin kthu t v m nhn cng tc o to v lnh vc ny.

IV. rong XTr:

y my gia tc c a vo xd ng trong iu trvc k c a nhiu thp nin trc y. Vi sthay i ny

to n

g vic lin quan n nhng thit b k thu t . Cng tc vt ltrong x thay i .

c lit k trong mc trn, tuy nhin mc c th c a cng tc vt l theo trnh t t nh o n cc cng tc hng ngy khikho bao gm:

hit b.

c x.

c.

tia electron.

p kho ch.

nh gi kho ch iu tr.

iu qu trong cng tc vt l, v l yu t quy t nh n cht lng iu tr c a trung tm cng nh m

ra.

Vt l trng: l ngi chu trch nhim chung vcng tc vt l trong khoa,trng l ngi nm bt v hiu rt r v cng tc v t l xtr c ng nhnh ng y

nghin cu, ph

Cc nhn vin Vt l khc: l nhng nh vt l c o to chuyn mn hoc cnhng kin thc chung vvt l x trv cng tc vt l trong x tr. Nhim v c anhng nh vt l ny l thc hin cc cng vic vt l hng ngy ca trung tm x theong quy trnh v yu cu ca cng tc xtr .

Cng Tc Vt L T

Ti Vit Nam, nhng nm gnang dn dn thay thcc my Co-60

n mt bc pht trin mi trong lnh vc c coi l p dng nhng kthu t cao trongy khoa. Song song vi vic p dng cc thit b hi n i vo i sng l s i hi nhng nhngi mi v con ng i v cn

tr c th ni l m t trong nhng s

Cng tc vt l trong mt trung tm x nh n y chng ta s phn tch thnh nh ng khung yu cu cho vic chun b ban u khi thnh lp khoa cha i vo hot ng. Cc cng tc

Xy dng hth ng l thuyt v hth ng lu trqu n l thng tin.

Xy dng chng trnh kim tra bo m cht lng trang t

Xy dng chng trnh an ton b

Kim chun v thu thp dli u chm tia.Cng tc kim tra v bo m cht lng my gia t

Cng tc o v chun liu lng chm tia photon v chm

nh gi, bo m cht lng dli u chm tia v h th ng l

Cng tc lp k ho ch iu tr.

Cng tc kim tra v

K ho ch pht trin v o to.

S quan tr ng ca mt quy trnh cng vic nh v y l v n xc nh c mc tiu,phng hng v yu cu cng vic r rng. Mt quy trnh r rng nu c hon thin st onn mt h th ng l thuyt khoa hc vi cch thc tch c, lu trv b o qun dli u h

bo v m t php l ca trung tm khi c cc cuc kin tng xy

ngha ca tng cng tc cth:

Xy dng h thng l thuyt v h thng lu trqun l thng tin: l vic xydng mt h th ng l lun v cc quy nh vcng tc V t L ti mt trung tm xtr b ng cchban hnh nhng vn bn, ti liu lin quan n cc cng tc vt l xtr , ni ln mc tiu v tmquan trng ca cc vn bn . N c xem nhm t quy trnh hay mt m hnh hot ng chocng tc vt l ti mt khoa x tr . Vic nh gi cc dli u thu thp c lin quan n cngtc vt l v x tr c a ra sau , t hng dn vic thit lp h th ng lu tr d li u



21/41

phbc xtham ktin nu

hp. Vic lu trd li u l mt yu cu quan trng lin quan n mt php l v an tonv nn c t ch c mt cch khoa hc, ngn np. Mt cch tt nht, vic lu trnn

ho phng php lu trd li u theo m hnh qun l dli u ca ngnh cng nghthngc th.

Xy dng chng trnh kim tra bo m cht lng trang thit b: y l vic thit

lpm bb tr vic i

ton bc x

mt chng trnh hon chnh vl thuy t v cc bn ti liu lin quan n vic kim tra vo cht lng cc trang thit bquan tr ng trong khoa. Vic xy dng ny nn c chunc khi khoa i vo hot ng v n s l ph ng hng hot ng v cng tc v t l khiu trtrn b nh nhn c tin hnh.

Xy dng chng trnh an : Ging nhvi c xy dng chng trnh kimbc xnn c xy dng tr t sm nhc th . N ni ln

s an ttra cht lng, chng trnh an ton

on v lao ng cng nhv an ton trong iu tr c a khoa. Chng trnh an ton baogm van ton b c xv an ton cho nhn vin. Ch ng trnh an ton boa gm nhng vn bnphp l lin quan, cc phng php theo di, x l v l u trd li u lin quan n vn anton.

Kim Chun V thu thp dliu chm tia: y l mt quy trnh thin vchuyn mnvt l i hi nhng ng gp vki n thc vt l v nhng k n ng ca cc nh vt l trong vicu thth p dli u. Cng tc ny c thc hin ngay nhng ngy u tin khi cc thit b c ci

t v y l khu chun b, kim tra trc khi a cc thit b vo iu trtrn b nh nhn.

Cng tc kim tra v bo m cht My Gia Tc: y l cng tc thng xuyn cacc nh vt l y khoa. Cng tc ny da trn l thuyt v cc ti liu c xy dng tch ngtrnh kim trong iu trvng gp ao (nh iu tr vi khung stereotacxy ho

Cng tc v chm tia Electron

tra v b o m cht lng trn. Cng tc ny nh gi schnh xcvo kt qu iu tr c bit trong nhng trng hp iu trk thu t c

c iu trchnh xc).

o v chun liu lng chm tia Photon : Cng tc

ny hon t lng my gia tc, n c thc hinda trn n n m cht lng. Cng tc nynh gi s y khoa.

ton c ngha ging nhcng tc ki m tra chh g kt quc c tch ng trnh kim tra v bo chnh xc v m t liu lng v mt cng tc quan trng vi cc nh vt l

nh gi, bo m cht lng dliu chm tia v HThng Lp KHoch: L mtcng tc k y khoa.Cng tc ng lp k ho ch c ng v a vo cng tciu trc

C

h quan trng i hi nhiu v cc ki n thc chuyn mn ca nhng nh vt lny c thc hin trc khi hth a khoa.

ng tc lp khoch iu tr: Cnc a tng quc gia, tng trung tm.

g tc ny c thni tu thu c vo h th ng o tov tch c Ti cc trung tm v cc nc tin tin c mt h

c trchn n m l sk t hp cht ch c a ngi lp k ho ch v

thng o to tt, mt i ng k thu t vin c o to chuyn mn tt sl ng i thc hin

cng tc lp kho ch xtr . Tuy nhin cc n c khc ni m hth ng o to v x tr ch ac hon chnh hoc cha c nh Vi t Nam th n l trch nhim ca cc nh vt l, mtkhc n ph thu c vo php l ca tng quc gia. Cng tc ny i hi vk n ng nhiu hn lv ki n thc chyn mn, nhng n l mt cng vic phc tp i hi st ng hp kin thc v Ykhoa v v V t l t c mt kho ch iu tr t t. Trong cng tc ny khng chhim ca cc nh Vt l hay Kthu t vi

nh Ung bu hc bc xv trong cc tr ng hp phc tp l cc nh chuyn mn Y khoa khc.

Cng tc kim tra v nh gi k hoch iu tr: Cng tc ny l bc th hai saucng tc lp k ho ch, n gm hai phn: kim tra v nh gi kho ch. Kim tra m bo bn k hoch c thc hin chnh xc v khng sai xt trong qu trnh lp kho ch. Cng tc ny i

hi s hi u bit chuyn mn ca cc nh Vt l v nn c xem l mt cng tc cn thit trongquy trnh iu tr b ng bc x t i cc trung tm xtr . Cng tc ny c thc hin bi cc nh



22/41

Vt l v l mt khu quan trng ti cc nc c ngnh x tr pht tri n. nh gi kho ch ltrch nhim ca cc nh Ung bu hc, vic nh gi kho ch cho bit k ho ch c hon hov s phn b li u, liu kim sot bu v liu kim sot bin chng hay khng. Vic nh gik ho ch tt nht l sk t hp ca chai i ng V t l v cc Nh ung bu hc. Vic kim

t b

tr v gip cc i ngnhn vin hi u nhau hnng nh

so u l mt cng tc kh quan trng. Mt trung tm x tr t ch c tt, vic nh gi khoch xtr s c ch trng, n s c gii thiu nhng trng hp tiu biu trc khoa vl ch th o lun rt kinh nghim v v Target, l a chn nng lng chm tia, la chn sphn b li u v nhng nh gi v li u lng. Tvi c nh gi k ho ch nhv y nhng thiust trong tnh ton liu, v target v th c hin iu trs c rt kinh nghim v ng gp rtnhiu trong vic ci tin nng cao kt qa iuc h c c nhiu hn vnh ng sai st trong x tr .

KHoch Pht Trin V o To: y l cng tc chy u ca cc nh lnh o, trong cth l vai tr c a ngi Vt l trng. N nh hng cho vic nng cao cht lng iu trhin ti thng qua hc tp rt kinh nghim chuyn mn v nh hng cho vic pht trin, trinkhai cc kthu t mi vo iu tr.

T y l s trnh by m t cch s l c v ngha, vai tr v v tr c a tng cng tc vt ltrong hot ng ca mt khoa iu tr. Tuy nhin cc thay i b xung hay thay i v nghav cch thc hin cn ty thuc vo thc t t ng trung tm.

TChc Nhn SVCng Tc Vt L:

rn

V.

cho cng tc lp k ho ch.

- 2

thc ch

y l vic btr, phn cng cng vi c cho cc nhn vin Vt l. Cng tc vt l trong xtrc nhi u phn khc nhau tu vo m i quc gia m cng tc vt l chia lm hai phn: cng tclin quan n lp kho ch v cng tc QA-QC. Vi t Nam hin nay do cha c trung tm oto vlnh vc xtr cho cc v t l y khoa v kthu t vin, do cng vic lin quan n lp k hoch l cng vic ca cc nh vt l.

Sb tr cng vi c cho i ng v t l do cng c thchia thnh hai ph n chuyn mn:lin quan Lp kho ch v vQA-QC. Vi c tch c nhn sd a trn hai mng chuyn mn nyl mt yu cu tt yu v l cng tc qun l, n thuc trch nhim trc tip ca ngi Vt ltrng v ban lnh o khoa.

Sb tr cng vi c c th phn chia nh sau: i vi mt trung tm xv i t nht hai mylp k ho ch v hai my gia tc, ti mt thi im nn c:

- 3 nhn vin

nhn vin kim tra kho ch v nhp thng tin

- 1 nhn vin cho cng tc m phng.

-

2 nhn vin cho cng vic QA-QC.S b tr s l ng nhn vin cho cc cng tc nh v y c tnh n s ki m tra cho

(Double check) trong mi cng tc m bo tnh an ton v hiu qu iu tr. i vi micng tc vt l trn i hi phi da theo nhng tiu chun c thng nht v ban hnhthnh vn bn hoc cng b trong nhm v t l v trong khoa. Cc cng tc trn phi c mbo v tnh nguyn t c trnh tnh tr ng khng thng nht trong cch nh gi kim tra, cngnhv y vic m bo cht lng iu trl d a trn nhng tiu chun chung nht, nhng kin

uyn mn c tho lun v thng nht. Mt scng tc trong ki m tra k ho ch vQA-QC i hi c tnh chuyn mn cao, do ti nhng khu ny cng yu cu mt n l c lnhn vchuyn mn.

Vic phn chia cng tc trn nn c phn cng r rng ng ngi ng vic c lchsp xp chi tit v c th . iu ny m bo c sho t ng c h th ng trong khoa v hnch tnh tr ng chng cho trong cng vic.



23/41

Nhng Vn Vt L CBn Trong XTr

Cc Loi Bc XPht Ra Tmy Gia tc c sdng trong xtr:

Nh c c p ph n trn v nguyn l ho t ng ca my gia tc tuyn tnh. Ccelectron c pht ra tsng b n electron c gia tc trong mi trng sng in tcao t n tti vn tc rt cao sau c bn vo mt bia tia X pht ra chm tia Photon.Nhv y chm bc xs d ng trong iu trx tr s l m t chm tia Photon, tuy nhin vi mygia tc cn c th s d ng trc tip chm tia electron cho mc ch iu trb ng cch cho phttrc tip chm electron m khng qua bia tia X.

I.

Cc ch

II.n Trong Mi Trng Vt Cht:

cc hin tng nhit c gi chungi, nng lng electron mt i t o ra nhng dngtrng v bc xhm pht ra t mi tr ng vt cht

c g

hn nng lng ca electron c chuyn sang tia X, n t

m tia Photon v Electron tmy gia t c c th c pht ra vi nhiu mc nng lngkhc nhau ty thuc sl a chn ca khch hng v nhu cu sd ng.

Bia Tia X Trong My Gia Tc Tuyn TnhII.1.STng Tc Ca Electro

Khi cho m t chm electron tng tc vo mt mi trng vt cht, cc electron mangnng lng cao ny sb m t nng lng do sva ch m v sb c x n ng lng. Nng lngca electron mt i do sion ha, m t do skch thch v dol sm t nng lng do va chm. Ngc lnng lng mi nhphoton, s b c x c

i chung l sm t nng lng do bc x. Nng lng electron mt i do va chm l nnglng ca electron bh p thtrong m t mi trng vt cht, v v vy ta c liu hp th, trongkhi s m t nng lng do bc x l n ng lng electron mt i t o ra cc bc x d ngphoton, v do trong trng hp ny ta c cc ngun pht tia X v liu chiu do ngun tia X pht ra. Hiu sut pht tia X chnh l pl v i bc s nguyn t c a vt liu bia, v t l v i l n nng lng ca electron th ba

(electron cc l p ngoi dch chuyn vl p l tr ng).

Hnh 1: Stng tc ca electron trong mi trng vt cht



24/41

II.2.Bia Tia X:

Nu cho mt chm electron tng tc vo mt bia mng v sau o cng tia X phtra ti nhng im cch u xung quanh bia ny, khi kt qu s t ng tc ca nhng chm

din nhv y c gielectron nng lng khc nhau ln bia s c chra nh hnh_2. Sbi ul sphn b gc c a tia X v bia mng trn c gi l bia tia X. Trong sphn b ny, kho ng

cch tbia t i ng biu din cng s cho bi t cng t ng i ca chm tia X ti migc cho trc. Da vo sphn b nh v y ngi ta c th k t lun rng :

Hnh 2: Sphn btheo gc ca tia X

V i chm electron nng lng thp, ni chung chm tia X c pht ra theo hng vunggc vi hng ca chm electron tng tc. Do ti nhng mc nng lng thp, bia tia X sc b tr nghing m t gc so vi hng ca chm electron ti v c gi l bia phn xahnh_3.

Hnh 3: Bia phn xv bia truyn qua

Ti nhng mc nng lng cao hn ni chung tia X s pht ra theo h ng ca chmelectron bn ti. Vi cc my x tr n ng lng cao nhmy gia t c tuyn tnh bia tia X s cbtr theo ki u ny. Chm bc xh u dng s c ly ra ti cnh pha bn kia ca bia, bia tia Xkiu ny c gi l bia truyn qua.



25/41

III.P hm Photon:

hc, nu khong cchtng tc rt nh (ch ng hn s t ng tc l trc din) th ton b n ng lng ca electron schuyn sang ch cho m t photon. V vy khi cho mt chm electron tng tc vi mt biatungsten ngi ta thy rng chm tia X sinh ra cha photon c nng lng t0 n nng lngln nht ca electron, y l s phn b n ng lng lin tc, v n ngc vi s phn b n nglng gin on ca chm photon tngu n Co-60.

i vi bc x c trng, nng lng ca bc x c trng ph thu c vo bc snguynt c a vt liu bia. Tm li, nng lng photon sinh ra t s t ng tc electron v ht nhnnguyn tph thu c vo nng lng cc i ca electon v cu trc nng lng ca vt liu bia.Tc l nu nng lng cc i ca electron ln hn nng lng lin kt cao nht ca nguyn tvt liu bia, ngi ta s thu c nhng photon pht ra do sd ch chuyn electron trong lp v nguyn tv t liu lm bia. V sau cng ph n ng lng photon ca mt chm tia X l pht ngcng ca bc xhm v b c x c trng.

hNng Lng C

Trong qu trnh t ng tc ca electron trong mi trng vt cht nh d c p trn, khicc electron tng tc vi in trng tnh in ca ht nhn nguyn t, chng s pht b c xhm v bc x c trng. Nng lng bc x hm ph thu c vo nng lng elctron mt i trongqu trnh tng tc , iu ny phthu c vo in trng tnh ca ht nhn v khong cch ca

s t ng tc (khong cch telectron n nhn). Vi mt vt liu lm bia cho trc, nng lngphoton pht ra s ph thu c vo khong cch tng tc. Hay ni cch k

Hnh 4: Phnng lng tia X l thuyt v thc nghim

Tm li ph b c x tia X g m hai thnh phn chnh: bc x hm v b c x c trng.

Trong bc x hm l ph n ng lng lin tc, v phb c x c trng l phb c x gin on(tng tph n ng lng ca photon tngu n ng v ). Ph n ng lng photon l tr t thp (t0) n gi tr c c i ca chm tia ti. Gi tr n ng lng cc i ny thng thng l bng inthgia t c ca my. Cui cng l ti vng nng lng thp hu ht cc photon nng lng thpu bh p th b i st l c.

IV.

hau. n v c a chm tia electron l MeV, v cc mc nng lng thng sd ng l 5Mev

n 14 hay 16MeV.

n VNng Lng Ca Cc Chm Tia Bc XTrong XTr:

Nhv y chm tia nc xt my gia t c tuyn tnh pht ra c thl chm tia Photon ho cElectron. Cc chm tia bc xny s c cc m c nng lng khc nhau ty thuc vo mc chiu tr v n vc a chng l khc n



26/41

ng v n ng lng ca chm tia photon l MV v cc mc nng lng thng c s

V.

dng l 4MV, 6MV, 10MV, 15 MV v 18MV. Nng lng chm tia cng tng th kh n ng xuyn su ca chm tia cng tng.

SPhn BNng Lng Ca Chm Bc XVi Mi Trng - SCn Bng Electron:

Scn b ng electron l mt hin tng xy ra trong phantom m, phantom m tng ngvi nguyn liu trong phantom c c tnh phng xgi ng m mm chng hn nh l c tnh vs tn x v s suy gi m. Cc nguyn liu phi c bc s nguyn t v n ng nh m m m,thng l nc. Mt snguyn li u khc nhlucite, masonite, wax .v.v. c ng c nhng c tnhnhm m m v vy cng c dng nhv t liu tng ng m.

Hnh 5: Squng chy ca Electron gn bmt phn cch m v khng kh

By gita s xem xt v s cn b ng ny, xt mt phantom m ln vi mt phn cch mkhng kh t ti khong cch SSD t ngu n. Cho mt chm photon c chiu vo b m tphantom, mt sphoton s t ng tc vi nguyn liu phantom v to ra nhng electron c vn tccao. Liu hp th trong mi tr ng l do sm t nng lng ca nhng electron trn qungng i ca chng trong mi trng. Mi electron c tm nh hng chtrong qung ng ica n do nh hng ca mi electron trong mi trng c th c biu din bi mt ngthng bng qung ng i ca n hnh_5. Nu gis r ng tt cnh ng qung ng l bngnhau v cng chiu vi chiu chm tia. V st ng tc ca mt photon hon ton l mt tin trnhngu nhin, v nu n im c um c b qua t c l khng c s photon t ng tc

h hng ca lut t l ngh ch bnh phng v ssuy gsuy gi m ca chm bc x trong m, th s

a nguyn li

ti bt c su no trong phantom s l gi ng nhau. khi s qung ng khi u ti tt c

cc su l b ng nhau. Liu hp thd i bm t m khng kh s ph thu c vo s track i qua su . S track b ng qua nhng su khc nhau c ch ra pha d i ca s . Nu strack ny c vnh l m t hm theo su, k t qus cho th y mt sthay i liu theo su.



27/41

Hnh 6: ng c tnh Build-up

T th hnh_6ta th y liu hp thb ng khng ti bm t, v tng tuyn tnh n mt su cc i bng qung chy electron, v sau n l hng s. Cng trong th ny ta c li u

hp th o thc t c biu din bng ng lin nt. C thth y rng hnh dng chung l gingnhau, nhng c mt vi s khc nhau quan tr ng. S khc nhau l do m hnh qung ngziczac ca electron, s suy gi m v s tn x c a chm photon trong phantom, v do lut t l nghch bnh phng khong cch. V v vy liu hp th trn b m t s khc khng. M t khcnhng electron c to ra bn ngoi phantom nh trong khng kh v trong c u trc collimatorni chung cng to ra mt liu hp th b m t gii hn. Ngoi ra ssuy gi m v lut tl ngh chbnh phng slm gi m lin tc cng chm tia, v v v y gim liu hp ththeo su. Do v tr li u hp thc c i l cng gi trnh ng ni chung ti mt su nh h n qung chyelectron.

Hi nhu ng ng hp tht ng tm t gi trth p ti bm t n mt gi trc c i xcc gi l hiu ng BUILD-UP. Vng liu hp thgia t ng ny c gi l vng Build-up. Tiv tr c c i, hoc su Build-up, ta ni t c mt iu kin cn bng electron. Vi iukin ny ti v tr , seletron vo th tch nh c a mi trng l bng vi selectron d i th tch . c tnh build-up c tm thy trong tt c cc chm photon v ty thu c vo nnglng ca chm tia. Cc chm tia nng lng khc nhau c trng bi su Build-up nh ch ratrong bng sau.

Chm Photon Nng lng cc i Nng lng trung bnh su Build-up100 KV250 KVCs_137

Co_606 MV10 MV

100 Kev250 Kev660 Kev

1.33 Mev6 Mev10 Mev

33 Kev80 Kev660 Kev

1.25 Mev2 Mev3.3 Mev

App. 00.2 mm1.5 mm

5 mm1.5 cm2 cm

25 MV 25 Mev 7 Mev 4 cm

Bng 1 : Chiu su khc nhau cho nhng chm photon khc nhau.

Cng tng tnh v y cc chm tia electron khi tng tc vi mi trng cng xy ra ccqu trnh tng tc tng tv c ng to ra vng Build-Up khi tng tc vi mi trng, nhngim khc bit ca chm tia electron vi cc chm tia photon l:- Ngay t khi ti p xc vi mi trng cc chm tia electron gy ra s t ng tc trc tip

ngay lp tc do liu ti bm t ca mi trng trong trng hp ny cao hn so vi cc

chm photon.



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- Cc chm tia electron c qung chy trong mi trng ngn, suy gim rt nhanh trong mitrng nn c ssuy gi m ngay sau vng Build-Up.

- Chm tia Electron l bc x ion ha tr c tip v chm tia photon l bc x ion ha gin ti p.

Hnh 7: Sphn bliu hp thca chm tia bc xtrong mi trng

- Chm tia Electron l bc x ion ha tr c tip v chm tia photon l bc x ion ha gin ti p.

- Chm tia Electron c qung chy gii hn trong mi trng, chm tia photon khng c qung

chy gii hn trong mi trng.

cVI. XV Trng Chiu:VI. ia

b c c t ra t mt n , v c h quan tr ng

chm t ng ch t ngu n :

Chm Tia B1. Chm T

m tiaBc X:

mt no Mt ch c xv th c xem nhm t hm nh sng phgun im hai c tn sau:

tit din ia t l v i bnh ph khong c2

22 d

11 d

=A

A

(1)

A1, A2 h t ng ng t chm gh ch vi bnh khong cch:

trong l din tc i d , d1 2ph ng

.cng tia t l n

2

21 dI

12 dI

= (2)

trong I1, I2 l c ng chm tia t i khong cch d1, d2 t ng ng.

Trong x tr chm tia b c x c th c pht ra tm t ngun ng vphng x (ngu n60) hay l chm tia bc x pht ra t m t my gia tc tuyn tnh. Nu l ngun ng v th

m ng vpht

Co-

ch ra l ng hng, nu l chm tia pht ra tm t my chiu xth s c nhhng theo mt hng hu dng no .



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V

tn

tch nht nh thng l din tch vung hay chnh t vi bm t cn chiu xg i l trng bcxhay trng chiu.

Hai im cn ch ca trng chiu l: hnh dng v kch thc ca trng chiu: chnh l din tch ca mt chm tia ti

mt khong cch cho trc tngu n bc x. Sut liu trong trng chiu:t i bt k m t im no bn trong chng chiu (trong

vng din tch ca trng chiu) Sut liu chiu u l mt hng skhc khng, v t ibt cv tr no bn ngoi tr ng chiu sut liu u l bng khng.

VII.Beam Profile V Penumbra:VII.1. Beam Profile:

I.2. Trng chiu ca chm tia Photon

T cc chm tia b c x pht ra ng i ta thng dng cc thit b che ch n ch n bchm tia bc xchi u ra t to ra mt chm bc x h ng theo mt li ra duy nht c mt di

Hnh 8: Beam profile ca trng hnh chnht

ng chiu ca mt chm bc xtrong khng

ng bc xd c theo ngMNPQ.

Beam profile: c nh ngha l sphn b li u t ng thng i quatrng. Nu by gi ta v m t ng thng xuyn qua tm v chia trng thnh hai phn bngnhau g hnh trn ta thy rng beam profile ca u l hng s, v ti miim bn ngoi trng sut liu u bng khng. Beam nhng trc chnh l rtquan trng, v thng thng ngi ta hay ch n bea o tr c chnh ca trng.

VII.2

h nh t ABCD l trT nh_8, gi s hnh ch kh. V ng thng MNPQ qua trng chiu v sau o st liu chiu hoc cng chmbc xd c theo ng ny, chng ta sthu c mt th su t liu hoc cng chm b c xdc theo ng MNPQ. th ny c gi lBeam Profile ca tr

chiu dc theo m

i l trc chnh ca trng (Principal Axis). Tng RS cho thy sut liu chiu ti bt c v tr no trong tr ng

profile d c theom profile dc the

. Penumbra ca chm tia:



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Hnh 9: nh hng ca lut tlnghch bnh phng

Nu ta xt mt trng chiu hnh chnh t hay hnh vung khi kch thc trng chiu

c vit l ab, trong a, b l di v r ng ca trng chiu. V tm i xng ca hnhchnh t c gi l tm trng chiu (im O). ng thng ni im O vi ngun bc x lng thng c khong cch ngn nht v c gi l trc chm tia (beam axis) hay trc trungtm chm tia(central axis).

Nu chng ta gi thi t rng ngun l ngun im v bc x pht ra t ngu n l nghng (isotropic), ng thi githi t rng ngun c bao bc bi vt liu hp thb c xv cmt li ra cho php to ra mt chm hay mt trng chiu c hnh dng v kch thc xc nhnh hnh_9.

Gi do l kho ng cch tngu n ti im O, gis su t liu ti im ny l 100. Ta xt ccim Q c khong cch d1t ngu n (d1> d0), sut liu ti im ny l:

X1 = 100 (d o/d1)2 < 100

Tng tta xt t i im A c khong cch d2 t ngu n (d2 > d1 > d0), sut liu ti ba im ny l:

X2= 100 (d o/d2)2< X 1= 100 (d o/d1)

2< 100

Hnh 10: Beam profile ca ngun im

Do ti nhng im cng cch xa im O th sut liu cng thp hn ti O. V vy cngtrong vng AB nh xt trn s khng l h ng s m gi m dn ttm ra bin nh ng

AB hnh_10. Ssuy gi m ny l do lut t l nghich bnh ph ng. Ngoi ra ti cc im ngoivng AB lun lun c mt % no ca bc x xuyn qua v t liu che chn. Cng chm b c



31/41

xxuyn qua c ng tun theo lut tl ngh ch bnh phng khong cch (RR v QQ trong hnh,trong RR l kt qu o c vi cht hp thdy h n).

Tm li, vi ngun im cng chm b c x l n nht ti tm trng chiu v gim dntheo khong cch ttm do lu t tl ngh ch bnh phng khong cch, sau gim t ngt nmt gi tr ph thu c vo s xuyn qua ch t hp th c a lp che chn ngun v sau cng gim

chm mt ln na theo lut t l ngh ch bnh phng khong cch. y l beam profile ca mtchm tia bc x.

Tuy nhin trong thc t ngu n ca cc my x tr khng ph i l ngun im m c thc coi l c kch thc nh hnh_11. Nu t kch thc ngun l S, khi nh hng ca mtngun c kch thc n beam profile s c minh ha nhsau:

Hnh 11: Beam profile ca ngun c kch thc

t D l khong cch tngu n n li ra (hay n bm t ca diapragms), d0 l kho ngcch tngu n n ti im O (tm trng). Xt phn trung tm ca beam profile (gia A v B):gis ngu n c chia thnh nhiu phn nhsao cho m i phn tng ng vi mt ngun im.Khi xut liu trong khong AB s l t ng s ng gp ca tt c cc ngu n im . Nhng

nhng im trong UA v BV li hon ton khc nhau. T cc im trong AB c th nhn th yton bngu n. Tuy nhin khi t i v tr Q, khi ch m t phn ca ngun l c th nhn th y vmt phn ngun kia bche b i vt liu che chn ngun. Kt qu l su t liu chiu ti Q l tng sng gp ca tt cnh ng ngun im c nhn thy ti vtr ny. V v y ti nhng im trongUA v VB cng s l t ng tt cnh ng s ng gp trc tip tnh ng ngun im c nhnthy cng vi s ng gp ca phn xuyn qua ca nhng ngun im khng nhn thy.

Ni chung Beam profile ca mt ngun c kch thc bao g :m Trc tin ti vng tru n thy ton b ngu n, v vy

sthay i cng trong vng ny l do qui lu t tl ngh ch bnh phng khong cch.ng tm (on AB), mi im u nh

Tip theo l pha ngoi vng UV, ti nhng v tr ny hon ton khng nhn th y ngun, vdo cng o c chy u chdo b c xchuy n qua vt liu che chn, sau tiptc c hiu chnh theo lut tl ngh ch bnh phng khong cch.



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Sau cng l nhng im trong vng UA v BV: Ti U l im khng nhn thy ngun vvy ch c b c x xuyn qua. Ng c li ti A ton b ngu n c nhn thy v v vy

t hn. Kch thc ca vng ny l UA, BV v ch y u do cc h s hnh h ch S,

cng t i y tng ng vi cng im trung tm. i vi nhng im gia U vA cng t ng dn tU t i A v cng tin vA ph n ngun nhn thy cng nhiu hn.Vng ny l c trng ca beam profile ca mt ngun c kch thc.

S thay i t ngt ca cng trong ngu n im c thay bi mt vng cng thay i t t ngn do v D to thnh. Vng ny c gi lPenumbrac a trng chiu. r ng ca vngpenumbra c th c tnh ton ttam gic ng dng hnh I-10, tam gic S1S2Z v ZUA l haitam gic ng dng, v vy:

hoc

=

ZS

ZASUA

1

AZ

UA

ZS

S=

1

Dd

D

ZA

ZS

=

0

1 v

=

= 100

D

dS

D

DdSUA (3)

i vi my gia tc trng c xc nh ti mt bm t cch ngun mt khong cch l 100cmgi l SAD, khi do

= SAD.

kch thc vng penumbra = [ ]

1

D

SADS (4)

Tbi u thc ny thy rng vngPenumbrathay i khi:

a) S : tng hoc gimb)

SAD: tng hoc gimc) D : tng hoc gim.

i vi my gia tc S l mt hng s, SAD=100cm khng i; D khng thay i v vyPenumbrac a mt chm tia photon tmy gia t c l khng i.

S t n ti ca vn tr ng bc x ph c tpn. K

VIII.

ng chmtrong my gia tc tuyn

so vpenumb

ngun,

g penumbra lm cho vic xc nh kch thch hng nh trong tr ng hp ngun im, kch thc trng c th d dng c xc nhbi r ng ca vng cng ch a b thay i t ngt. Trong trng hp ngun c kch thc,kch thc trng tbc x l hai l n r ng t tm n v tr li u t 50% so vi liu ti tm(im O). R rng kch thc trng trong trng hp ny ln hn AB nhng nh h n UV.

Sng u Ca Trng :

Trong iu tr, thng thng cn c mt chm bc x v i mt cng ng u trnton vng tit din ca n v ngi ta mun c mt liu ng u cho khi u. Trong iu kin ,ngi ta mun bt u vi mt chm tia ng u n c th d dng thay i theo mong muntrong mt trng hp c bit no . Tt cnh ng my gia tc u c mt blm ph tia tia nh hnh_12. V tr c a blm ph ng chm tia l cc k quan trngtnh nng lng cao n nh hng n ph ng (flattness) v i xng (symetry) ca chm tia.

V vyphng (flatness) ca trng c nh ngha l sthay i ln nht ca cngi gi trcng ti tm chm tia trong trng (hay trong beam profile), ngoi trvngra. ph ng ca trng ph thu c vo ba h s : kch th c trng, khong cch tc tnh t nhin c a ngun.



33/41

Hnh 12: Sdng b tia X nng lng cao

ph ng v i xng ca trng l hai yu t lin quan n tnh an ton trong vnhnh thit b, khi mt trong hia gi trny t khi mt g i hn quy nh my gia tc sng ngpht tia.

lc chm

v i



34/41

Nhng Thng SVt L CBn Trong Tnh Ton Liu

I.Gii Thiu:

Trong chng trc chng ta a ra nh ngha beam profile. Beam profile c dngm t s thay i liu hoc sut liu trong mt phng ngang theo cc trc chnh ca trng bc

x. Tuy nhin sm t ny th c cht nhv y, v trong thc tbeam profile nn c m tbachiu. Ton bhnh nh ba chiu s l m t bc tranh rt thc t, v n cn thit trong s d ngthc t.

Mc tiu ca xtr ngoi l cung cp mt liu thch hp v ng u cho mt vng thtch no , ng thi cng cn ch n skhc nhau vliu cho nhng cquan trng yukhc.Beam profile m c d cha mt sthng s v t l quan trng nh phng chm tia, kchthc trng, kch th ng. Tuy nhin chnh

ng thng s

II. h trc OAF:Beam profile th hi n nhng gi tr t ng i o c dc theo trc chnh ca trng.

Nhng gi tr o c ny trong thc t l m t phn b3 chi u v c sd ng tnh ton li ukhi c kt hp thm cc hs hi u chnh ring khc. Trong tnh ton liu Beam profile th hi nsut liu chiu hay liu chiu tng i ca nhng im trong trng chiu ngoi trc trung tmca chm tia so vi sut liu chiu hay liu chiu ti tm trng chiu. V vy n c s d ng tnh ton li u ti nhng im ny t th hi n mt s phn b li u ba chiu trong trngchiu v vic o hs l ch trc thc cht chnh l vic o c beam profile nh hnh_1.

c penumbra, v struyn qua pha ngoi ca trnh ny c ng khng th c hin vic nh liu cho mc ch iu tr. Nhng s liu m t trong ch ng ny s gip chng ta hi u hn trong vic tnh ton phn b li u.

Hslc

OAF

0.0000,

0.2000,

0.4000,

0.6000,

0.8000,

1.0000,

1.2000,

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Hnh 1: Biu din ca hsOAF

III.HsOutput:

Mt h s v t l quan trng khc cn thit trong vic xc nh liu lng thng qua vico cxut liu chiu hay cn gi l Output ca my ti tm trng chiu. V trong trngchiu sut liu chiu thay i t v tr ny sang v tr khc, nn n gin ngi ta chn tm



35/41

trng chiu l tr ny c ngl sut liu chi

c o c bng bung ion ha trong mt phantom nc, gi tr o c tbu ng

X = Xp(1 + k) (3)

m chun v n l im dxc nh. Thng thng sut liu chiu ti vu cc i ca trng.

Outpution ha s bao g m hai thnh phn: thnh phn sc p v thnh phn ng gp ca tn x. Trong thnh phn sc p l nhng phonton n trc tip tngu n, v nhng photon tn x c to

ra ts t ng tc ca chm photon sc p vi cc lp che chn nhcollimator N u ta gi X lliu chiu tng, Xp l thnh ph n liu chiu do chm sc p, v Xs l thnh ph n liu do photontn xt o thnh, khi ta c th vi t nhsau:

X = Xp + Xs (1)

Xp ph thu c vo m nh ca ngun v khong cch tngu n (theo lut t l ngh ch bnhphng khong cch), nhng khng ph thu c vo cu trc vt l my nh c u trc cacollimator. Xsph thu c vo cng chm photon s c p, v v vy, n ph thu c vo tt ccchs m chm photon s c p phthu c vo. Do ngi ta c thvi t :

Xs= k .X p (2)

Trong gi trk ph thu c vo cu trc hnh hc v c tnh vt l ca collimator. T ta thy rng sut liu chiu ph thu c vo k, tc l ph thu c vo cu trc hnh hc v c tnh vtl ca thit bche ch n nhcollimator v v y hs Output s thay i ph thu c vo cu trchnh hc v c tnh vt l ca thit b che ch n hay phthu c vo Collimator

Nu sut liu chiu ti mt khong cch cho trc tngu n c o theo sthay i cakch thc trng chiu bng cch thay i ci t collimator, ngi ta thy rng nhng gi tr l khc nhau.

Hnh 2: nh hng ca tn xtheo gc mca Collimator

S thay i c th th y c theo hnh_2. Ba s trong hnh ng vi SSD nh nhau,nhng c gc mcollimator khc nhau t o ra nhng kch thc trng khc nhau aa, bb vcc. Trong mi trng hp, ta o sut liu chiu ti tm ca trng chiu, chn mt im Q

chung ti bm t collimator v c thxem nhm t ngun bc x tn x . Thnh phn sc pca sut liu chiu trong mi trng hp l khng i v ngun v khong cch t ngu n nim o l khng i (SSD khng i). nu xt trng trung bnh b b, nh ng photon tn xtrnh th ng collimator v n im o. Tuy nhin vi trng kch thc nh h n nh a a, ccphoton tn xny c th l i bt ng tc vi cu trc collimator mt ln na, v v vy s khngc ghi nhn bi detector. Sau cng vi kch thc trng rt ln, nhc c, gc tn xl khngthun li v v vy mt ln na khng T ngi ta c th tinon rng, sut liu tng theo k i tr cc i v gim ttkhi

g rt ln.

c ghi nhn bi detector.ch thc trng, tin ti mt g

kch thc trn

Th c t, sut liu chiu cho nhng trng kch thc khc nhau c biu din bi

sut liu tng i v gi l Output Factor. Gi s su t liu chiu cho trng c hnh dng v



36/41

kch thc khc nhau l Xa, Xb, v gi s X rl su t liu chiu ca mt trng chiu c chnlm chun thng l 10x10 cm. Output factor c th c nh ngha nhsau:

OFq= X q/ Xr (4)

Trong OFq l Output Factor v Xq l sut liu chiu cho trng q x q. Hnh_3m t hnh dng ca h s Output Factor theo nh ng m Collimator khc nhau.

Hnh 3: Sthay i ca hsOutput theo kch thc trng chiu

Output factor l h s c lp vi m nh ngun. N c sd ng trong nhng trng

c trng cho sci t collimator.

IV.Phn Trm Liu Su (PDD):

Khi kho st sphn b li u ca chm tia bc x torng mi tr ng ngi ta bit rng sto ra vng build-up v mt im liu hp thc c i. im liu hp th c c i ny l duy nht,n l im nm trn trc trung tm v ti su d m. Nu ta o liu hp th t i nhng su khcnhau th ta c th t o ra mt ng cong m t s thay i liu hp ththeo chi u su gi l sphn b li u theo su. S phn b li u theo su ny gip cho vi c tnh ton li i nhng su khc nhau. Tuy u c i th bd liu ny c lp vi Ouput ca my v dli u ny c gi l phn trm liu su hay gi

hp tnh liu cho nhng kch thc trng khc nhau ti mt khong cch SSD chn trc. Do hs ny khng cho ta kch th c trng, m l ts su t liu chiu cho nhng ci t collimatorkhc nhau, tc l ts su t liu chiu cho nhng kch thc trng khc nhau. Hay ni cch khcoutput factor

u tcnhin, nu chng c biu din bng s h ng % ca li

l PDD.

Hnh 4: M tphp o PDD



37/41

Vi c xc nh PDD c thc hin bng cch o c liu ti nhng su khc nhautrong mt phantom nc. Trong hnh_4, im P cho thy im liu cc i, v

Q l mt im no

trong phantom. PDD ti im Q sau

ng iu kin o nh

thi gian pht tia, kch thc trng chiu, SSD v cht lng chm bc xkhng i. m t ton bchm bc x trong m t phantom, vic thit lp bng gi trPDD trong m t mng ba chiul rt cn thit tnh ton li u ti cc im khc nhau, ti nhng su khc nhau trong phantom.Nhng biu din v dng dli u nhv y sr t trng i. C mt tp hp dli u con n gin vhu dng hn: n l gi trPDD d c theo trc trung tm, c gi l PDD trc trung tm. Nhnggi tr PDD cho nh ng nng lng photon khc nhau vi kch thc trng chiu v SSD khcnhau c thit lp thnh bng. Mi trng khi s c biu din bi mt ct gi trPDD t inhng su khc nhau. M c d nhng gi tr khng mang thng tin v ng u chm tiahoc c tnh penumpra, nhng chng c s d ng rng ri cho y hc do tnh n gin trongbiu din.

c xc nh nh :

PDD(Q) = [D(Q)/D(P)] x 100 (5)

trong D(P) v D(Q) l liu hp tht i P v Qt ng ng trong c

Hnh 5:ng phn bliu hp ththeo su

Khi nng lng chm photon tng vng build-up cng s t ng do su c c i dm l nhn v qung chy electron rng hn v PDD ca chm tia cng tng theo nng lng.Khi kch thc hoc hnh dng ca mt trng bc x thay i PDD tng hu nh tuy n tnh tkch thc trng rt nh, sau tng t t v t n gi tr c c i ti mt vi kch thctrng ln hn.

V.SPhn Bng Liu:

Ts phn b li u ti cc su khc nhau chng ta bi t c ng c trng Build Upv PDD dc theo trc trung tm ca chm tia t kt hp v i cc h s khc c th tnh tonc liu hp th t i cc im d c a chm tia. Hay ni

i bm t phn cch dc trc trung tm



38/41

cch khc ta c th thu c sphn b li u dc theo trc trung tm. Nhng trong thc tin ngita cn bit liu trn ton thtch c a khi bu v vy nhng thng sli u dc trc trung tm lkhng , v liu ti nhng im bn ngoi trc trung tm cng cn c tnh ton. tnh tonc liu trong mt vn th thi t l t bng PDD cho tt cnhng im trong trng v t c u ti bt k

g th tch nh v y ngi ta c p mchi u bng mt mng ba chiu th tnh ton li

im no trong vng th tch c chiu. Nhng vic tnh ton thit lp bng liu nh v y lkhng thch hp cho vic biu din sphn b li u lng v trong thc tng i ta cn sphn b liu trc quan hn. V vy khi p dng vo thc tin vic biu din liu tng i thng cthc hin trn mt mt phng hai chiu theo dng ca mt sphn b ng liu. Thun li cavic sdng sphn bhai chiu l: sbiu din n gin, ngi ta c thbiu din dliutheo dng mt chui nhng ng cong ng liu gi l ng ng liu v mt phn bnhvy gi l sphn bng liu.

Hnh 6: Beam profile v sphn bng liu

Nhng ng thng hoc ng cong ng liu l nhng ng giao ca b m t ngliu v mt phng c chn la. thu c mt ng cong ng liu trong mt mt phngchn trc l rt n gin. Liu hp th t i mt s l n nhng im trong mt bm t trc tinc o sau nu ni tt c nh ng im liu bng nhau li vi nhau ta s c mt ng congl ng ng liu v hnh dng nhng ng c th tin on c. Trong hnh_6, gi s profile chm tia c bit trc. t Z l mt im bn trong phantom, nm trn trc trung tm

sao cho PDD l 50%. By u di bm t phantom.PDD ti X c tin on l thgi xt im X khc im Z, nhng cng sp hn ti Z do ba l do:

im X xa ngun hn im Z (lut bnh phng khong cch)RX l ln hn OZ v v vy sh p th t i X ln hn ti ZS ng gp phn tn x t h n

Do , mt im vi mt liu phn trm su PDD l 50% d c tia RYX phi l mt kho ng cch ngn hn slm t ng liu n 50%. Tng t, ngi ta

iu 50% cho nhng tia khc v kt qu ng cong ng liu 50%

biu din kiu ny l mt th ng liu. Nhng th ng liu ny c sd ng hi n th

im nm pha trn X c thxc nh nhng im lc ch ra. ng ny khi t ti su c a liu cc i dm, phi ct ti V m cng trn beam profile l 50%, v l kch thc trng su ny trong phantom. C nh v y ta c

th thu c ng cong ng liu cho nhng PDD khc. mt tp hp nhng ng ng liu



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s phn b li u trong ton vng thtch chi u tia nh gi sphn b li u lng trn ton bvng thtch .

Thng SCa Chm Tia Nng Lng Cao TMR v TPR:

Vi cc h s l ch trc OAF, hs collimator v s phn b li u theo su chng ta

c th tin on v tnh ton c mt sbi u din phn b li u ti cc im bt k trong m tvng th tch chi u x. Tuy nhin chng ta cha thhon ton tch ton c gi tr li u hp thhay cc gi trci t tham schi u cho my nhMU hay th i gian chiu. tnh ton c liuhp tht i mt im hay tch ton cc gi tr MU nh v y chng ta cn thm cc thng s quantrng khc. Cc thng s ny c m i quan hv i cc gi trc a sphn b li u theo su PDD.Tuy nhin ty thuc vo vng nng lng s d ng trong iu cng ty thuc spht tri n ca lnhvc iu trb c xng i ta c cc

VI.

tham s khc nhau nh PSF, TAR, TMR v TPR.

Cc tham s PSF v TAR th ng c p dng cho cc chm tia nng lng thp v ccphp o c thc hin o c trong khng kh vi mt Buildup-cap, tuy nhin vi cc chm tiabc x n ng lng cao v s tnh chnh xc h n cc nh hng trong c th cc php o trongkhng kh khng cn ph hp v su li u cc i dm l n hn khng nh hng n php oPDD, nhng gy nh hng ti php o TAR.

Vi photon nng lng cao khi thc hin cc php o trong khng kh ngi ta sc n mtbuilup cap ln t 8-10 cm ng knh, v build-up cap ny s tr thnh m t phantom c kchthc ln v s tn x trong phantom buildup cap ny l khng th trnh kh i, c bit vi kchthc trng nh s tn x l quan tr ng. V d cho tr ng 4 x 4 cm2, r rng builup cap ln hnkch thc trng, v gi tr c c tbu ng ion ha phi cha mt thnh phn tn x. V sion ha tp hp trong bung l chy u to bi st ng tc ca photon trong build-up cap, v gitr c c lc ny l gi trtrung bnh c a ton b th tch build-up cap. M t khc mt buildup-cap dy cng lm suy gim chm tia ng k, v v vy gi tr c c t bu ng s bi u dinthnh phn s c p suy gim. V l do ny hai s h ng mi TMR (t s m c c i: Tissue-

maximum-ratio) v TPR (ts m phantom: tissue-phantom-ratio) c a vo sdung. M c dnhng s h ng ny c s d ng trong tnh ton liu ging nh trong tr ng hp TAR, nhngchng c mt ngha khc vi TAR.

TMR v TPR:

tm hi u v h s TMR v TPR tr c tin ta xt m hnh o nh hnh_7, s bn tri,im P c t trn trc chnh ti khong cch SAD tngu n, bn trong mt phantom nc xcnh c trng chiu l A v ti su d . Trn s ph i tng tnh v y, ngoi tr d ynguyn liu pha trn im P thay i td thnh d. TMR c nh ngha l:

TMR(A,d) = ( liu hp th v i d cm phantom)/ ( liu hp thv i d cm phantom)

= D(A,d)/D (A,d ) (6)

m

m

m

m m



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Hnh 7: M hnh php o TMR v TPR

ch rng gi trTMR t i dms chnh xc b ng 1. Nu liu hp tht i dmbi t trc, Dm(A,dm),liu ti su khc D(A,d) c th c xc nh nhm i lin hsau:

a TMR chnh l s xc nh ca Dm. Bit rng vi nhngng cao, dm la mt hm ca kch thc trng (v dm t chm tia 5 x 5 cm

2ng 4 cm. Nhng vi chm tia rng hn, bc x tn x c quynh h ng y d

n v

ng mi, t s mphantom

ngha ca TPR tng tn d ml im chun, ngi ta chnmt su ti n li ln hn cho mi kch th r th ph i hnh_7). Khi TPR cnh ngha nhsau:

TPR = (liu hp tht i im d cm phantom)/ (liu hp th t i im drcm phantom)

Schu n ha sau s c thc hin trong phantom ti su d r, su chu n thay vdm. TPR c sd ng tng tnh TMR, TPR l d li u tnh ton li u.

Mt khc cc gi trTMR v TPR c th c tnh ton tcc gi tr c a PDD, v trongthc t thu n tin trong vic o c dli u chm tia cc php o phn bli u theo su PDDs c o c cho cc kch thc trng chiu khc nhau sau cc gi tr TMR ho c TPR s

c tnh ton tcc gi tr PDD o c theo cng thc.

D(A,d) = Dm(A,dm) x TMR(A,d) (7)

Dmc th c xc nh mt cch th nghim trong phantom v ngi ta a ra mt s h ng khc,hs li u tng i (RDF) v c nh ngha nhsau:

RDF(A) = Dm(A,dm)/ Dm(trng chun,dm) (8)

Vi RDF o, liu cho mt vi trng c thtnh ton b i slin h sau:D(A,d) = Dm(trng chun,dm) x RDF(A) x TMR(A,d) (9)

Mt vn trong nh ngha c

( ) ( )

( )

( )

( )

2

**,

,,

=

r

d

rp

dp

rd

dddd

SourcetoD

SourcetoD

DS

DS

DFDD

DFDDDFTPR

chm photon nng l25 MV, d khom mh pha b m t, tc l vi chm tia 30 x 30, dms l 1.5 cm). Do cu hi t ra l ngita sthay i im chun dmnh th no khi kch th c trng thay i th a mn nh nghiTMR. Nu iu ny c thc hin, khi stnh ton li u sr t phc tp, c bit khi lut t l nghch bnh phng c p dng vo. y l l do cho vic a vo s h

TPR.

hTMR nh ng thay v chnc t ng (



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VII.Cc hstnh liu khc:Ngoi cc hs gii thiu trn tnh ton li u hp tht i cc im trong vng th

tch c chiu xd i iu kin iu trchng ta c n mt s cc h s khc bao g m:1. H s truy n qua block2. H s wedge3. Khong cch ngun o

Ngoi ra ty theo thut ton tnh ton liu sc n phi s d ng thm cc tham skhc nhau, nh ngcc tham strnh by trn l cc tham s c b n nht.

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