28/10/20151 First FRCR Examination in Clinical Radiology Diagnostic Radiology & Radionuclide Radiology (4b) Patient Dosimetry John Saunderson Radiation Protection Adviser

28/10/20152 RCR Syllabus Methods Diagnostic reference levels (including high dose techniques) Magnitude and measurements.

28/10/20153 Methods General radiology Fluoroscopy Computed Tomography Nuclear Medicine.

28/10/20154 General radiology ESD –Thermoluminescent dosemeter (TLD) –exposure factors Dose-Area Product (DAP) Effective dose.

28/10/20155 T.L.D. Crystals, e.g. lithium fluoride Radiation causes electrons to be caught in “traps” At lab. TLDs heated to 240 o C Electrons released, light emitted Amount of light emitted proportional to dose.

28/10/20156 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).

28/10/20157 Using exposure factors kV, mAs, field size, FSD If D = dose at 100 cm for 80 kV, 100 mAs then ESD = D x kV 2 /80 2 x mAs/100 x /FSD 2 x BSF BSF = backscatter factor, depends on HVL and field size.

28/10/20158 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 = 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 /80 2 x 50/100 x /75 2 x 1.33 = 0.17 mGy.

28/10/20159 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.

28/10/ Dose Area Product Because dose falls with 1/d 2 and area increases with d 2, DAP is independent of distance.

28/10/ 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.cm 2, or Gy.cm 2,  Gy.m 2 ).

28/10/ 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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28/10/ Fluoroscopy Dose-Area Product (DAP) Exposure factors Effective dose.

28/10/ 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.

28/10/ Exposure factors Based on assumed FSDs, etc.

28/10/ Effective dose Can be “fudged” using radiograph software.

28/10/ GAFCHROMIC film

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25 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

28/10/ Computed Tomography CT Dose Index (CTDI) Dose-Width Product (DWP) Effective dose

28/10/ CT Dose Index (CTDI) Applies to a single slice Can be used to compare –different slice widths –different physical filter –different scanners –etc.

28/10/ 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.

28/10/ Effective dose NRPB program similar to radiography one

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28/10/ CT dose/risk calculation e.g. wrong patient referred for CT scan (laryngectomy)

28/10/ Nuclear Medicine MIRD Add up dose to each organ from the dose irradiating from each organ.

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28/10/ Diagnostic Reference Levels Early 80’s survey DRLs today IRMER

28/10/ Mid-80’s survey Method Survey of twenty UK hospitals 13 most common views For each patients (60-80kg) at DAP or ESD by TLD measured.

28/10/ 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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28/10/ Mid-80’s survey Recommendation Use 75 th 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.

28/10/ DRLs today A DRL is essentially a guide to the rather indistinct border between “good and normal practice” and “bad and abnormal practice”.

28/10/ 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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28/10/ Staff and Environmental Monitoring Devices –TLD –OSLD –Film –Electronic Body Extremity Environment

28/10/ Relevant measurement techniques

28/10/ Measuring Dose Luxel dose badges TLD finger rings –Can be cold sterilized –Heat sensitive

28/10/ 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.

28/10/ Electronic Dosemeters Used by Radiation Physics staff to test x-ray unit and measure environmental doses

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28/10/ 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 NotesDerived FALSE ARCHER, MS G, /09/201330/09/2013Chest MEASURED FALSE ARCHER, MS G, /09/201330/09/2013Right Finger MEASURED FALSE ATKINSON,A, /09/201330/09/2013Chest MEASURED FALSE AVERY, DR G, /09/201330/09/2013Chest MEASURED FALSE AVERY, DR G, /09/201330/09/2013Left Finger MEASURED FALSE AVERY, DR G, /09/201330/09/2013Right Finger MEASURED FALSE AZOR, B, /09/201330/09/2013Chest MEASURED FALSE BAJALAN, L, /09/201330/09/2013Chest Component Note: H-UnusedMEASURED FALSE BARLOW, NICHOLAS, /09/201330/09/2013Chest Component Note: H-UnusedMEASURED FALSE BEADLE, MRS E, /09/201330/09/2013Chest Component Note: H-UnusedMEASURED FALSE BEADLE, MRS E, /09/201330/09/2013Right Finger MEASURED FALSE BOTTOMLY, JAYNE, /09/201330/09/2013Chest Component Note: H-UnusedMEASURED 1 BOWERING, SUE, /09/201330/09/2013Chest ABSENT FALSE BRAMALL, M, /09/201330/09/2013Chest MEASURED FALSE BROWN, SUSAN, /09/201330/09/2013Chest MEASURED FALSE BYASS, DR O, /09/201330/09/2013Chest Component Note: H-UnusedMEASURED FALSE BYASS, DR O, /09/201330/09/2013Left Finger MEASURED FALSE BYASS, DR O, /09/201330/09/2013Right Finger MEASURED FALSE CAST, DR J, /09/201330/09/2013Chest MEASURED FALSE CAST, DR J, /09/201330/09/2013Waist overapronMEASURED FALSE CAST, DR J, /09/201330/09/2013Right Finger MEASURED YTD = year to date Luxel badge results (Sept 2013, CHH Radiology)

28/10/ 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 NotesDerived FALSE ARCHER, MS G, /09/201330/09/2013Chest MEASURED FALSE ARCHER, MS G, /09/201330/09/2013Right Finger MEASURED FALSE ATKINSON,A, /09/201330/09/2013Chest MEASURED FALSE AVERY, DR G, /09/201330/09/2013Chest MEASURED FALSE AVERY, DR G, /09/201330/09/2013Left Finger MEASURED FALSE AVERY, DR G, /09/201330/09/2013Right Finger MEASURED FALSE AZOR, B, /09/201330/09/2013Chest MEASURED FALSE BAJALAN, L, /09/201330/09/2013Chest Component Note: H-UnusedMEASURED FALSE BARLOW, NICHOLAS, /09/201330/09/2013Chest Component Note: H-UnusedMEASURED FALSE BEADLE, MRS E, /09/201330/09/2013Chest Component Note: H-UnusedMEASURED FALSE BEADLE, MRS E, /09/201330/09/2013Right Finger MEASURED FALSE BOTTOMLY, JAYNE, /09/201330/09/2013Chest Component Note: H-UnusedMEASURED 1 BOWERING, SUE, /09/ /09/2 013Chest ABSEN T FALSE BRAMALL, M, /09/201330/09/2013Chest MEASURED FALSE BROWN, SUSAN, /09/201330/09/2013Chest MEASURED FALSE BYASS, DR O, /09/201330/09/2013Chest Component Note: H-UnusedMEASURED FALSE BYASS, DR O, /09/201330/09/2013Left Finger MEASURED FALSE BYASS, DR O, /09/201330/09/2013Right Finger MEASURED FALSE CAST, DR J, /09/201330/09/2013Chest MEASURED FALSE CAST, DR J, /09/201330/09/2013Waist overapronMEASURED FALSE CAST, DR J, /09/201330/09/2013Right Finger MEASURED Luxel badge results

Absent Badges Participant Name, Number Begin wear date End wear date Dosimeter Location Body Dose (mSv) Extremit y Dose (mSv) Body Dose YTD Extremity Dose YTD NotesDerived FALSE C##T, DR J, /09/201330/09/2013 Chest MEASURED FALSE C##T, DR J, /09/201330/09/2013 Waist overapron MEASURED FALSE C##T, DR J, /09/201330/09/2013 Right Finger 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 = mSv for year

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