14/03/22 1 First FRCR Examination in Clinical Radiology Diagnostic Radiology & Radionuclide Radiology (4b) Patient Dosimetry John Saunderson Radiation Protection Adviser
28/10/20151 First FRCR Examination in Clinical Radiology Diagnostic Radiology & Radionuclide Radiology (4b) Patient Dosimetry John Saunderson Radiation.
Jan 13, 2016
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21/04/23 1
First FRCR Examination in Clinical Radiology
Diagnostic Radiology & Radionuclide Radiology
(4b) Patient Dosimetry
John SaundersonRadiation Protection Adviser
21/04/23 2
RCR Syllabus
•Methods
•Diagnostic reference levels (including high dose techniques)
•Magnitude and measurements .
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Methods
• General radiology
• Fluoroscopy
• Computed Tomography
• Nuclear Medicine .
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General radiology
• ESD– Thermoluminescent dosemeter (TLD)– exposure factors
• Dose-Area Product (DAP)
• Effective dose .
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T.L.D.
• Crystals, e.g. lithium fluoride• Radiation causes electrons to be caught in
“traps”• At lab. TLDs heated to 240oC• Electrons released, light emitted• Amount of light emitted proportional to dose .
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T.L.D.s +/-
+ Small+ Tissue equivalent+ Read 1 Gy+ Easy for radiographer
- No direct readout- Sensitive to heat, UV,
dirt- Tricky to calibrate- Easy to loose- Special ones needed for
low dose (e.g. chest) .
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Using exposure factors• kV, mAs, field size, FSD• If D = dose at 100 cm for 80 kV, 100 mAs
then• ESD = D
• x kV2/802 • x mAs/100 • x 1002/FSD2 • x BSF
• BSF = backscatter factor, depends on HVL and field size.
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E.g.• What is ESD for 100 kV, 50mAs, 15 x 15 cm field, 75 cm
FSD for Room 3?• From annual survey
– @ 80 kV, D = 9.1 mGy/100mAs @ 1 m– HVL for 100kV was 3 mmAl
• From tables– BSF for 3mmAl, 15 x 15 field = 1.33
• Therefore, entrance surface dose= 9.1mGy x 1002/802 x 50/100 x 1002/752 x 1.33
= 0.17 mGy .
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Using exposure factors +/-
+ No fiddly TLD for radiographers!
+ No fiddly TLDs for physicist!
+ Radiographers can calculate ESDs
+ No minimum dose
- No direct readout- Exposure parameters
must be recorded- Assumes tube output not
changed from last survey.
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Dose Area Product
• Because dose falls with 1/d2 and area increases with d2, DAP is independent of distance.
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DAP +/-
+ No fiddly TLD for radiographers!
+ Only one number to record
+ Instant answer
- Doesn’t take into account backscatter
- Initial cost (several thousand £)
- Units sometimes cause confusion (cGy.cm2, or
Gy.cm2, Gy.m2) .
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Effective dose
• Complicated to calculate from ESD or DAP
• Can use computer models which make assumptions on– field size– patient size– field position
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Fluoroscopy
• Dose-Area Product (DAP)
• Exposure factors
• Effective dose .
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DAP +/- for fluoroscopy
+ Instant answer, etc.+ DAP moves with the
tube+ Gives good indication of
relative risks of inducing cancer
- Not directly linked to erythema risk.
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Exposure factors
• Based on assumed FSDs, etc.
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Effective dose
• Can be “fudged” using radiograph software.
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GAFCHROMIC film
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GAFCHROMIC film
• optical density is proportional to the absorbed dose• 0.01 Gy to 50 Gy • Energy independent from 30 keV to 30 MeV• £20 per 14” x 17” sheet
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Computed Tomography
• CT Dose Index (CTDI)
• Dose-Width Product (DWP)
• Effective dose
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CT Dose Index (CTDI)
• Applies to a single slice
• Can be used to compare– different slice widths– different physical filter– different scanners– etc.
dzTN
zDCTDI
mm
mm
50
50
100
)(
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Dose-Length Product (DLP)
• DWP = CTDI x n x T
• Gives an idea of relative dose for a whole scan
• Can be used to compare effect of pitch, etc.
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Effective dose
• NRPB program similar to radiography one
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CT dose/risk calculation• e.g. wrong patient referred for CT scan
(laryngectomy)
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Nuclear Medicine
• MIRD
• Add up dose to each organ from the dose irradiating from each organ.
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Diagnostic Reference Levels
• Early 80’s survey
• DRLs today
• IRMER
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Mid-80’s surveyMethod
• Survey of twenty UK hospitals
• 13 most common views
• For each 10-20 patients (60-80kg) at
• DAP or ESD by TLD measured.
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Mid-80’s survey Results
• E.g. Chest PA– Median ESD = 0.18 mGy– Minimum ESD = 0.03 mGy– Maximum ESD = 1.43 mGy– Max / min = 48 !!.
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Entrance Surface Dose (mGy) Radiograph
Min. Median 3rd Quartile Max.
Lumbar spine AP 0.8 7.7 10 59
Lat 2.4 20 30 108
LSJ 7.4 35 40 131
Abdomen AP 0.7 6.7 10 62
Pelvis AP 0.9 5.7 10 32
Chest PA 0.03 0.2 0.3 1.4
Lat 0.14 1.0 1.5 11
Skull AP 0.7 4.0 5 14
PA 1.8 4.3 5 13
Lat. 0.4 2.2 3 9
Dose-area product (Gy.cm2) Radiograph
Min. Median 3rd Quartile Max.
Lumbar spine
(3.4 films)
2.0 12 15 93
Barium enema
(8.5 films, 224 s fluoro)
6.2 41 60 272
Barium meal
(7.8 films, 193 s fluoro)
0.5 17 25 163
IVU
(8.2 films)
3.3 29 40 251
Abdomen
(1.4 films)
0.7 5 8 30
Pelvis
(1.1 films)
0.49 4 5 19
21/04/23 38
Mid-80’s surveyRecommendation
• Use 75th percentile as reference value
• i.e. carry out local surveys and take action if average dose is greater than ¾ of national survey doses
• e.g. for chest PA reference = 0.3mGy ESD
• Send results to NRPB to review national reference doses every 5 years.
21/04/23 39
DRLs today• A DRL is essentially a guide to the
rather indistinct border between “good and normal practice” and “bad and abnormal practice”.
21/04/23 40
IRMER
• National DRLs – set as 3rd quartile– average from survey of “standard patients”– should be below DRL
• Local DRLs– ?Average for Trust?– Most should be below average
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Staff and Environmental Monitoring
• Devices– TLD– OSLD– Film– Electronic
• Body
• Extremity
• Environment
21/04/23 48
Relevant measurement techniques
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Measuring Dose
• Luxel dose badges
• TLD finger rings– Can be cold sterilized– Heat sensitive
21/04/23 50
Luxel badges
• Wear underneath lead rubber apron
• Assume dose to badge = effective dose
• Can be worn for 2 weeks to 3 months (usually 1 month)
• Must be returned promptly.
21/04/23 51
Electronic Dosemeters• Used by Radiation Physics staff to test x-ray unit
and measure environmental doses
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Absent Badges
Participant Name, Number
Begin wear date
End wear date
Dosimeter Location
Body Dose (mSv)
Extremity Dose (mSv)
Body Dose YTD
Exremity Dose YTD
Notes Derived
FALSE ARCHER, MS G,00176 01/09/2013 30/09/2013 Chest 0.1 1.27 MEASURED
FALSE ARCHER, MS G,00176 01/09/2013 30/09/2013 Right Finger 0.2 1.2 MEASURED
FALSE ATKINSON,A,00308 01/09/2013 30/09/2013 Chest 0.03 0.18 MEASURED
FALSE AVERY, DR G,00298 01/09/2013 30/09/2013 Chest 0.04 0.24 MEASURED
FALSE AVERY, DR G,00298 01/09/2013 30/09/2013 Left Finger 0.2 9.6 MEASURED
FALSE AVERY, DR G,00298 01/09/2013 30/09/2013 Right Finger 0.2 23.7 MEASURED
FALSE AZOR, B,00587 01/09/2013 30/09/2013 Chest 0.02 0.1 MEASURED
FALSE BAJALAN, L,00325 01/09/2013 30/09/2013 Chest Component Note: H-Unused MEASURED
FALSEBARLOW,
NICHOLAS,00053 01/09/2013 30/09/2013 Chest Component Note: H-Unused MEASURED
FALSE BEADLE, MRS E,00609 01/09/2013 30/09/2013 Chest Component Note: H-Unused MEASURED
FALSE BEADLE, MRS E,00609 01/09/2013 30/09/2013 Right Finger 0.2 1.2 MEASURED
FALSEBOTTOMLY, JAYNE,00694 01/09/2013 30/09/2013 Chest Component Note: H-Unused MEASURED
1BOWERING, SUE,00279 01/09/2013 30/09/2013 Chest ABSENT
FALSE BRAMALL, M,00588 01/09/2013 30/09/2013 Chest 0.01 0.03 MEASURED
FALSE BROWN, SUSAN,00326 01/09/2013 30/09/2013 Chest 0.03 0.07 MEASURED
FALSE BYASS, DR O,00384 01/09/2013 30/09/2013 Chest Component Note: H-Unused MEASURED
FALSE BYASS, DR O,00384 01/09/2013 30/09/2013 Left Finger 0.2 13.3 MEASURED
FALSE BYASS, DR O,00384 01/09/2013 30/09/2013 Right Finger 0.2 14.9 MEASURED
FALSE CAST, DR J,00376 01/09/2013 30/09/2013 Chest 0.01 0.99 MEASURED
FALSE CAST, DR J,00376 01/09/2013 30/09/2013 Waist 0.48 4.13 overapron MEASURED
FALSE CAST, DR J,00376 01/09/2013 30/09/2013 Right Finger 1.1 14.8 MEASURED
YTD = year to date
Luxel badge results(Sept 2013, CHH Radiology)
21/04/23 54
Absent Badges
Participant Name, Number
Begin wear date
End wear date
Dosimeter Location
Body Dose (mSv)
Extremity Dose (mSv)
Body Dose YTD
Exremity Dose YTD
Notes Derived
FALSE ARCHER, MS G,00176 01/09/2013 30/09/2013 Chest 0.1 1.27 MEASURED
FALSE ARCHER, MS G,00176 01/09/2013 30/09/2013 Right Finger 0.2 1.2 MEASURED
FALSE ATKINSON,A,00308 01/09/2013 30/09/2013 Chest 0.03 0.18 MEASURED
FALSE AVERY, DR G,00298 01/09/2013 30/09/2013 Chest 0.04 0.24 MEASURED
FALSE AVERY, DR G,00298 01/09/2013 30/09/2013 Left Finger 0.2 9.6 MEASURED
FALSE AVERY, DR G,00298 01/09/2013 30/09/2013 Right Finger 0.2 23.7 MEASURED
FALSE AZOR, B,00587 01/09/2013 30/09/2013 Chest 0.02 0.1 MEASURED
FALSE BAJALAN, L,00325 01/09/2013 30/09/2013 Chest Component Note: H-Unused MEASURED
FALSEBARLOW,
NICHOLAS,00053 01/09/2013 30/09/2013 Chest Component Note: H-Unused MEASURED
FALSE BEADLE, MRS E,00609 01/09/2013 30/09/2013 Chest Component Note: H-Unused MEASURED
FALSE BEADLE, MRS E,00609 01/09/2013 30/09/2013 Right Finger 0.2 1.2 MEASURED
FALSEBOTTOMLY, JAYNE,00694 01/09/2013 30/09/2013 Chest Component Note: H-Unused MEASURED
1BOWERING, SUE,00279
01/09/2013
30/09/2013 Chest
ABSENT
FALSE BRAMALL, M,00588 01/09/2013 30/09/2013 Chest 0.01 0.03 MEASURED
FALSE BROWN, SUSAN,00326 01/09/2013 30/09/2013 Chest 0.03 0.07 MEASURED
FALSE BYASS, DR O,00384 01/09/2013 30/09/2013 Chest Component Note: H-Unused MEASURED
FALSE BYASS, DR O,00384 01/09/2013 30/09/2013 Left Finger 0.2 13.3 MEASURED
FALSE BYASS, DR O,00384 01/09/2013 30/09/2013 Right Finger 0.2 14.9 MEASURED
FALSE CAST, DR J,00376 01/09/2013 30/09/2013 Chest 0.01 0.99 MEASURED
FALSE CAST, DR J,00376 01/09/2013 30/09/2013 Waist 0.48 4.13 overapron MEASURED
FALSE CAST, DR J,00376 01/09/2013 30/09/2013 Right Finger 1.1 14.8 MEASURED
Luxel badge results
Absent Badges
Participant Name, Number
Begin wear date
End wear date
Dosimeter Location
Body Dose (mSv)
Extremity Dose (mSv)
Body Dose YTD
Extremity Dose YTD
Notes Derived
FALSEC##T, DR J,00376 01/09/2013 30/09/2013 Chest 0.01 0.99 MEASURED
FALSEC##T, DR J,00376 01/09/2013 30/09/2013 Waist 0.48 4.13 overapron MEASURED
FALSEC##T, DR J,00376 01/09/2013 30/09/2013
Right Finger 1.1 14.8 MEASURED
Luxel badge results
Effective dose assumed to be underapron dose. 0.99mSv to end Sept, so predicted annual dose = 12/9 x 0.99 = 1.32mSv for year
Finger dose, 4.13 to end Sept, so predicted annual dose = 12/9 x 14.8 = 19.73 mSv for year
21/04/23 56
f i n
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