Conversion from LDR to HDR Intracavitary Brachytherapy for Cancer of the Cervix Bruce Thomadsen University of Wisconsin Madison.

Conversion from LDR to HDR Conversion from LDR to HDR Intracavitary Brachytherapy for Cancer Intracavitary Brachytherapy for Cancer

of the Cervixof the Cervix

Conversion from LDR to HDR Conversion from LDR to HDR Intracavitary Brachytherapy for Cancer Intracavitary Brachytherapy for Cancer

of the Cervixof the Cervix

Bruce ThomadsenBruce Thomadsen

University of WisconsinUniversity of WisconsinMadisonMadison

Learning ObjectivesLearning ObjectivesLearning ObjectivesLearning Objectives

1.1. To understand the different variables in LDR and To understand the different variables in LDR and HDR intracavitary brachytherapy for cancer of the HDR intracavitary brachytherapy for cancer of the cervix.cervix.

2.2. To understand the procedures for HDR intracavitary To understand the procedures for HDR intracavitary brachytherapy for cancer of the cervix.brachytherapy for cancer of the cervix.

HDR Advantages for HDR Advantages for Cervical Ca TreatmentsCervical Ca TreatmentsHDR Advantages for HDR Advantages for

Cervical Ca TreatmentsCervical Ca Treatments1.1. Shorter treatment times, resulting in:Shorter treatment times, resulting in:a)a) Outpatient treatment.Outpatient treatment.b)b) Less patient discomfort since prolonged bed rest is Less patient discomfort since prolonged bed rest is

eliminated eliminated c)c) Treating patients intolerant of isolation or at risk for acute Treating patients intolerant of isolation or at risk for acute

cardiopulmonary toxicity due to prolonged bed rest.cardiopulmonary toxicity due to prolonged bed rest.d)d) Reduced applicator movement during therapy.Reduced applicator movement during therapy.e)e) Greater displacement of nearby normal tissues.Greater displacement of nearby normal tissues.f)f) Possibility of treating larger number of patients.Possibility of treating larger number of patients.

HDR Advantages for HDR Advantages for Cervical Ca TreatmentsCervical Ca TreatmentsHDR Advantages for HDR Advantages for

Cervical Ca TreatmentsCervical Ca Treatments

2.2. Allows use of smaller diameter sources than are Allows use of smaller diameter sources than are used in HDR:used in HDR:a)a)Resulting in less patient discomfort, thereby;Resulting in less patient discomfort, thereby;b)b) Reducing the need for dilatation of the cervix Reducing the need for dilatation of the cervix

and therefore reducing the need for heavy sedation or and therefore reducing the need for heavy sedation or general anesthesia (allowing treatment for high-risk general anesthesia (allowing treatment for high-risk patients who are unable to tolerate general patients who are unable to tolerate general anesthesia).anesthesia).

c)c)Making insertion of the tandem into the cervix easier.Making insertion of the tandem into the cervix easier.

HDR Advantages for HDR Advantages for Cervical Ca Cervical Ca TreatmentsTreatments

HDR Advantages for HDR Advantages for Cervical Ca Cervical Ca TreatmentsTreatments

3.3. Tailor dose distribution to target Tailor dose distribution to target through optimizationthrough optimization

4.4. Elimination of exposure to personnelElimination of exposure to personnel

Disadvantages of HDR Disadvantages of HDR BrachytherapyBrachytherapy

Compared with LDRCompared with LDR

Disadvantages of HDR Disadvantages of HDR BrachytherapyBrachytherapy

Compared with LDRCompared with LDR Labor intensive (requires large staff during Labor intensive (requires large staff during

procedure)procedure) Decreased therapeutic ratio (radiobiologically, Decreased therapeutic ratio (radiobiologically,

normal tissue becomes relatively more sensitive normal tissue becomes relatively more sensitive than tumor)than tumor)

Increased probability of executing an errorIncreased probability of executing an error Must know target and desired dosesMust know target and desired doses

Dangers of HDR BrachytherapyDangers of HDR BrachytherapyDangers of HDR BrachytherapyDangers of HDR Brachytherapy Working fastWorking fast

– so patient doesn’t become uncomfortable and start so patient doesn’t become uncomfortable and start to moveto move

– so patient doesn’t develop thrombosesso patient doesn’t develop thromboses– so patient doesn’t stay under anesthesiaso patient doesn’t stay under anesthesia

Lots of input data required (≈ 350 bits of Lots of input data required (≈ 350 bits of information)information)

complicated to check by handcomplicated to check by hand

Steps in Converting from LDR to Steps in Converting from LDR to HDR Intracavitary BrachytherapyHDR Intracavitary BrachytherapySteps in Converting from LDR to Steps in Converting from LDR to HDR Intracavitary BrachytherapyHDR Intracavitary Brachytherapy

1.1. Determine dose and fractionationDetermine dose and fractionation

2.2. Determine applicatorDetermine applicator

3.3. Determine dwell positionsDetermine dwell positions

4.4. Determine optimization schemeDetermine optimization scheme

5.5. Establish quality managementEstablish quality management

Biological Equivalence:Biological Equivalence:Dose per FractionDose per Fraction

Biological Equivalence:Biological Equivalence:Dose per FractionDose per Fraction

LDR LDR BED = D { 1 + [2D(BED = D { 1 + [2D()/)/ ] [ 1 - <1- exp(- ] [ 1 - <1- exp(-T)>/(T)>/(T)]} T)]}

- 0.693T/(- 0.693T/(TTpp))

HDR HDR

BED = n d [ 1 + d/(BED = n d [ 1 + d/() ] - 0.693T/() ] - 0.693T/(TTpp))

d

2

4D

n

1 2 Ý D

1 1 e T

T

2

••

Biologically Biologically Effective Effective Dose vs. Dose vs.

DoseDose

Biologically Biologically Effective Effective Dose vs. Dose vs.

DoseDose

0

50

100

150

200

BE

D

0 10 20 30

Dose [Gy]

Biologically Effective Dose vs. DoseFor some treatment regimens

1 Fx HDRTumour

1 Fx HDRNormal

5 Fx HDRNormal

5Fx HDRTumour

LDRTumour

LDRNormal

Therapeutic Ratio vs. Dose RateTherapeutic Ratio vs. Dose RateTherapeutic Ratio vs. Dose RateTherapeutic Ratio vs. Dose Rate

0

0.2

0.4

0.6

0.8

1T

hera

peut

ic R

atio

0.0

1

0.1 1

10

10

0

10

00

Dose rate [Gy/h]

Therapeutic Ratio as a Function of Dose Rate

Continuous 20:2

Continuous 10:3

Fractioned 20:2

Fractioned 10:3

Living with Unfavorable Living with Unfavorable Therapeutic RatioTherapeutic Ratio

Living with Unfavorable Living with Unfavorable Therapeutic RatioTherapeutic Ratio

The save graces are:The save graces are:Geometric spacing - With HDR Geometric spacing - With HDR

brachytherapy, normal structures brachytherapy, normal structures can be held away during can be held away during treatment; andtreatment; and

Fractionation.Fractionation.

ImprovementImprovementinin

TherapeuticTherapeuticRatioRatio

with Increasing with Increasing Number of Number of FractionsFractions

ImprovementImprovementinin

TherapeuticTherapeuticRatioRatio

with Increasing with Increasing Number of Number of FractionsFractions

1

2

3

4

5

6P

erc

en

t im

pro

ve

me

nt

0 5 10 15

Number of fractions

Ao

Af

XX

X

Ao

Af

2 cm2 cm

2 cm2 cm

X

raduis

VdVs

0.5 cm

ABS ABS Recommendations for Recommendations for

Locating Point ALocating Point A

ABS ABS Recommendations for Recommendations for

Locating Point ALocating Point A

Absolute DoseAbsolute DoseAbsolute DoseAbsolute Dose The treatment usually has external beam The treatment usually has external beam

treatments to about 44 - 50 Gy at 1.7 - 2.0 treatments to about 44 - 50 Gy at 1.7 - 2.0 Gy/fraction.Gy/fraction.

Total treatment to about 100 - 110 GyTotal treatment to about 100 - 110 Gy1010.. Typical HDR regimen is 5 fractions of 5.5 Typical HDR regimen is 5 fractions of 5.5

Gy.Gy. Chemotherapy strongly affects both normal Chemotherapy strongly affects both normal

tissue and tumor reaction.tissue and tumor reaction.

What if I used theWhat if I used theM.D. Anderson Approach?M.D. Anderson Approach?

What if I used theWhat if I used theM.D. Anderson Approach?M.D. Anderson Approach?

Review a selections of patients with Review a selections of patients with a variety of applications and a variety of applications and determine the doses to Points A.determine the doses to Points A.

What if I Didn’t Use theWhat if I Didn’t Use theM.D. Anderson Approach?M.D. Anderson Approach?What if I Didn’t Use theWhat if I Didn’t Use the

M.D. Anderson Approach?M.D. Anderson Approach?

You should still review a set of your You should still review a set of your patients and look at the shape of the patients and look at the shape of the dose distribution. (Not that you want dose distribution. (Not that you want to duplicate that - it was what you to duplicate that - it was what you could get, not what you wanted to get.)could get, not what you wanted to get.)

Cervical Ca TargetsCervical Ca TargetsCervical Ca TargetsCervical Ca Targets


1.1. Determine dose and fractionationDetermine dose and fractionation





Cervical Ca TargetsCervical Ca TargetsCervical Ca TargetsCervical Ca Targets

Tandem and CylindersTandem and CylindersTandem and CylindersTandem and CylindersBecause of the nature of Because of the nature of the anisotropy, this the anisotropy, this maximizes the relative maximizes the relative contribution to the contribution to the bladder and rectum per bladder and rectum per dose to cervix, and dose to cervix, and usually prevents adding usually prevents adding distance to those distance to those organs.organs.

ShortShortdistancedistance

0.5cm0.5cm

PoorPoorDepth doseDepth dose

PoorPoorContributionContribution

Tandem & Ring GeometryTandem & Ring GeometryTandem & Ring GeometryTandem & Ring Geometry Simple but complex Simple but complex

geometry geometry Ring diameterRing diameter

– Ring + Cap diameterRing + Cap diameter

– 36mm, 40mm, 44mm36mm, 40mm, 44mm

– constant 6mm source to constant 6mm source to surfacesurface

Tandem AngleTandem Angle– 30°, 45°, 60°30°, 45°, 60°

– 2cm, 4cm, 6cm, 8cm2cm, 4cm, 6cm, 8cm

Jason Rownd, Medical college of WisconsinJason Rownd, Medical college of Wisconsin

Tandem & Ring GeometryTandem & Ring GeometryTandem & Ring GeometryTandem & Ring Geometry

Fixed geometry - tandem fixed in Fixed geometry - tandem fixed in center of ringcenter of ring

Choose combination according to Choose combination according to anatomyanatomy

Dosimetry needed only for 1st Dosimetry needed only for 1st fraction?fraction?

Adapt fraction to fraction if Adapt fraction to fraction if neededneeded


Dosimetry Methods-TandemDosimetry Methods-TandemDosimetry Methods-TandemDosimetry Methods-Tandem

Dose optimization points Dose optimization points are tapered along the are tapered along the tandem axistandem axis

12mm, 14mm, 16mm, 12mm, 14mm, 16mm, 18mm,20mm down to level 18mm,20mm down to level of Point Aof Point A

Dwell locations down to Dwell locations down to ringring



Tandem length will affect Tandem length will affect the dose around Point Athe dose around Point A

– more tandem dwells, less more tandem dwells, less relative contribution from relative contribution from ring dwellsring dwells

– goal percentage 100%, goal percentage 100%, optimized 90-110%optimized 90-110%



Tandem length will affect Tandem length will affect the dose around Point Athe dose around Point A

– more tandem dwells, less more tandem dwells, less relative contribution from relative contribution from ring dwellsring dwells

– goal percentage 100%, goal percentage 100%, optimized 90-110%optimized 90-110%


Dosimetry Methods-RingDosimetry Methods-RingDosimetry Methods-RingDosimetry Methods-Ring Dwell locations are Dwell locations are

specified as part the specified as part the prescriptionprescription

– 4, 5, or 6 dwells to a side4, 5, or 6 dwells to a side

Dose optimization points Dose optimization points are placed radially at 6mmare placed radially at 6mm

– non radial placement means non radial placement means different depths and not on different depths and not on ring surfacering surface


Ao

Af

XX

X

Ao

Af

2 cm2 cm

2 cm2 cm

X

raduis

VdVs

0.5 cm

Tandem and Tandem and OvoidsOvoids

Tandem and Tandem and OvoidsOvoids


1.1. Determine dose and fractionation.Determine dose and fractionation.





HDR and HDR and LDR LDR T&OT&O

HDR and HDR and LDR LDR T&OT&O

LDR HDR

Duplicate the LDR Source Distribution Duplicate the LDR Source Distribution with HDR Dwell Weights?with HDR Dwell Weights?

Duplicate the LDR Source Distribution Duplicate the LDR Source Distribution with HDR Dwell Weights?with HDR Dwell Weights?

Can we? Certainly, and a lot of work was Can we? Certainly, and a lot of work was done to do this well in the late 1980s.done to do this well in the late 1980s.

Should we? Absolutely not!Should we? Absolutely not!– Duplicating the physical distribution does not Duplicating the physical distribution does not

duplicate the biological distribution because duplicate the biological distribution because BED depends on dose/fraction.BED depends on dose/fraction.

– Fails to give the patient the benefit of Fails to give the patient the benefit of optimization.optimization.

Selecting Dwell Selecting Dwell PositionsPositions

Selecting Dwell Selecting Dwell PositionsPositions

Unused (Spacing)

Add spacing in tip to protect Add spacing in tip to protect bowel.bowel.

Load tandem to about mid-Load tandem to about mid-ovoid.ovoid.

Ovoid use dwells 2-8.Ovoid use dwells 2-8.– Dwell 1 irradiates rectum.Dwell 1 irradiates rectum.– Dwell 9 irradiates bladder.Dwell 9 irradiates bladder.







A Sample of A Sample of OptimizationOptimizationA Sample of A Sample of OptimizationOptimization

X

2 cm

X

1.8 cmX

X

XX

XX

Unused (Spacing)

1 cm

2 cm Pt. A

Tip dwells to variable Tip dwells to variable for optimizationfor optimization

Tandem dwell inferior Tandem dwell inferior to Pt. A hard to to Pt. A hard to specifyspecify

Need to place points Need to place points for ovoidsfor ovoids

Optimization SchemeOptimization SchemeOptimization SchemeOptimization Scheme Specify relative doses to the optimization Specify relative doses to the optimization

points (e.g., 100% tandem points, 125% points (e.g., 100% tandem points, 125% ovoid points with chemo - depends on Pt A ovoid points with chemo - depends on Pt A Dose)Dose)

Use optimization on dose points,Use optimization on dose points, Distance optimization.Distance optimization. Minimize the dwell gradient weighting Minimize the dwell gradient weighting

factorfactor..







Quality ManagementQuality ManagementQuality ManagementQuality Management

Things to check:Things to check:

1.1. Dose specification (right dose - right point)Dose specification (right dose - right point)

2.2. Applicator (right geometry)Applicator (right geometry)

3.3. Dose distribution (right doses - right places)Dose distribution (right doses - right places)

4.4. Normal Tissue doses (in tolerance)Normal Tissue doses (in tolerance)

5.5. Correct programming (right source movement Correct programming (right source movement - right catheter)- right catheter)

6.6. But I’ve talked about that before.But I’ve talked about that before.

Physicist’s Physicist’s Worksheet Worksheet for Tandem for Tandem and Ovoidsand Ovoids

Physicist’s Physicist’s Worksheet Worksheet for Tandem for Tandem and Ovoidsand Ovoids

HDR DOSIMETRY CHECKTreatments Using Tandem and Ovoids

Check in the box indicates parameter is correct.

Date: MR#: Patient: Fraction No. of Disease & Stage: Dose/Fraction from protocol:

1. Location and Dose Checks____ a. Dose for this fraction on Rx __________ Gy Average dose to applicator points __________ Gy____ b Difference between right and left A and prescribed dose is less than 5%____ c Distance of Point A (Starting from midovoid line)

Distance cephalad as defined in Rx ________ mm Distance cephalad on films ________ mmDistance lateral as defined in Rx ________ mm Distance lateral on printout _______ mm

Distance lateral on coronal plane _______ mm____ d Ovoid cap sizes

Rt Visible marker ______ Rt size ________ mm Rt Distance to vaginal dose points ________ mmLt Visible marker ______ Lt size ________ mm Lt Distance to vaginal dose points ________ mm

____ e Dose percentile to vaginal surface ___________ % of Rx dose = __________ Gy and isodose lineson the plan fall on the vaginal surface

____ f Starting dwell for tandem on plan corresponds to start indicated on film Dwell #:_________________ g Bladder ____________ Gy ( ____________%) Rectum _____________ Gy ( ____________%)

__________ Physician alerted if > 70%2. Time Checks:____ a Time index for dwell 1 cm from first dwell Index ________ Posted range ______ to __________ b Time index for total time Index ________ Posted range ______ to __________ c Total Time Index from previous treatmentIndex ________ Agree within 5%3. Program Transfer Check____ a Morning QA length

Rt. ovoid programmed to channel 1 Length for this channel Lt. ovoid programmed to channel 2 Length for this channel Tandem programmed to channel 3 Length for this channel

____ b Step size ________ 2.5mm ________ 5.0mm____ c Patient’s file has been saved.4. Programming of the HDR Unit____ Dwell times, positions, length and step size on print out match that from the computer planningAll the appropriate checks above prove satisfactory

Checking Physicist Time Date

Index 1 = Dwell time #5 x Source strength

Dose to Pts M

Index 2 = Total dwell time x Source strengthDose to Pts M x Number of dwells

Index 2' = Total dwell time x Source strength

Dose to Pts M x Total treatment length x 2.0 cm

dist.

Indices FormulaeIndices FormulaeIndices FormulaeIndices Formulae

ABS Recommendations for HDR ABS Recommendations for HDR Cx Brachytherapy: 1Cx Brachytherapy: 1


1.1. Brachytherapy must be included as a component Brachytherapy must be included as a component of the definitive radiation therapy for cervical of the definitive radiation therapy for cervical carcinoma.carcinoma.

2.2. Good applicator placement must be achieved to Good applicator placement must be achieved to obtain improved local control, survival and obtain improved local control, survival and lower morbidity.lower morbidity.

3.3. HDR should be interdigitated with pelvic EBRT HDR should be interdigitated with pelvic EBRT to keep the total treatment duration to less than 8 to keep the total treatment duration to less than 8 weeks.weeks.



4.4. The relative doses given by EBRT versus The relative doses given by EBRT versus brachytherapy depend upon the initial volume of brachytherapy depend upon the initial volume of disease, the ability to displace the bladder and disease, the ability to displace the bladder and rectum, the degree of tumor regression during rectum, the degree of tumor regression during pelvic irradiation, and institutional preference.pelvic irradiation, and institutional preference.

5.5. Interstitial brachytherapy should be considered Interstitial brachytherapy should be considered for patients with disease that cannot be optimally for patients with disease that cannot be optimally encompassed by intracavitary brachytherapy.encompassed by intracavitary brachytherapy.

Conversion from LDR to HDR Intracavitary Brachytherapy for Cancer of the Cervix Bruce Thomadsen University of Wisconsin Madison.

Documents

dose slide

personnel slide

hand slide

hdr advantages

dose rate slide

dangers of hdr brachytherapy

t t p slide

quality management slide