X-Ray Patient Doses A Strategy for Evaluation & Recording

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1 X-Ray Patient Doses A Strategy for Evaluation & Recording Bogdan OLTEANU M.D. Valentin PARASCHIVA Phy. Codrut CHERESTES Phy. Margareta CHERESTES Phy. Emergency Children s Hospital Grigore Alexandrescu Bucharest, Romania

2 Objectives To be aware of what different dose units mean Evaluate the Thermo-Luminescent Detector (TLD) measurements Plan a strategy for patient-dose recording that fits daily practice, is physically correct and has a meaning in evaluating individual and populational risks.

3 Some Basic Knowlege ugy (TL D) mas POL YMOBIL E 125 kv TE L E DIAG NOS T 125 kv POL YMOBIL E 70 Kv TE L E DIAG NOS T 70 Kv POL YMOBIL E 40 kv TE L E DIAG NOS T 40 kv The dose varies linearly with mas but also varies strongly with KV and significantly with technical differencies between X-Ray units

4 ugy (TL D) Some Basic Knowlege Dos es by F iltering (Telediagnost, 50 mas, 1.5m) F ilter: +0 F ilter: +2Al Filter: +0,2C u+1al P ower (F ilter: +0,2C u+1al) P ower (F ilter: +2Al) y = 0,0443x 2,295 R 2 = 0,9989 y = 0,0021x 2,8754 R 2 = 0, U, kv The dose varies with KV by a power equation and varies strongly with technical differencies between X-Ray units: -beam filtering -generator type

5 How to measure patient doses at X-Rays? Effective Dose (Sievert <Sv>) Measure radiation absorbed in the body, balanced by risk-related coefficients Is proportional with risk (deaths because of late cancers) Adds together radiation effects on different organs Different various irradiations (Rg, Fluoro, CT, Scinti, PET) can be added in a period of time or lifelong Best tool, but complicated to measure TLDs within a plastic phantom or TLDs on the patient skin and use of math. phantoms

6 How to measure patient doses at X-Rays? Incident dose (Gray <Gy>) Measure incident radiation (that enters the body) Indirect estimation of the absorbed dose and related risk It s not additive (Chest Rg + Lumbar Rg + Head CT...) Not the best unit, but easy to measure Single TLD on the patient skin in the center of X-ray beam Therefore chosen as Reference for Plain X-Rays!!! Includes the back-scatter

7 How to measure patient doses at X-Rays? Incident dose (Gy) Easy to measure, Reproducible, Standardized Reference-Doses available for standard patients : 70 Kg adult, 5 year old child, baby Reference Doses available for common X-Rays: Chest, Skull, Spine, Pelvis, Abdomen,... Comparisons are possible: Between practices Between a practice and the reference-doses Can lead to evaluation of the Effective Dose <Sv> Not easy!!!

8 X-Ray Doses ugy (Log scale!) Reference doses Chest (newborn) Chest (baby) Chest (5 y child) Chest lateral (5 y child) Chest (adult 70 Kg) Pelvis (5 y child) Abdomen (5 y child) Skull lateral (5 y child) Skull (5 y child) Chest lateral (adult 70 Kg) Skull lateral (adult 70 Kg) X-Ray type Skull (adult 70 Kg) Abdomen (adult 70 Kg) Pelvis (adult 70 Kg) Lumbar spine (adult 70 Kg) Lumbar spine lat (adult 70 Kg) Lumbo/sacral lat (adult 70 Kg)

9 X-Ray Doses ugy (Log scale!) Reference doses Median / Achievable doses HF X-ray units Tw o-pulses monophasic unit Chest (newborn) Chest (baby) Chest (5 y child) Chest lateral (5 y child) Chest (adult 70 Kg) Pelvis (5 y child) Abdomen (5 y child) Skull lateral (5 y child) Skull (5 y child) Chest lateral (adult 70 Kg) Skull lateral (adult 70 Kg) X-Ray type Skull (adult 70 Kg) Abdomen (adult 70 Kg) Pelvis (adult 70 Kg) Lumbar spine (adult 70 Kg) Lumbar spine lat (adult 70 Kg) Lumbo/sacral lat (adult 70 Kg)

10 How to measure patient doses at X-Rays? Personal Film-Dosimeters (F.D.) -alternative to TLDs The measurable dose-range covers all common X-rays (Almost) invisible on radiographs (Previous work of the same workgroup) First film (low doses) Second film (high doses) ugy R 2 = 0,9694 ugy R 2 = 0, O.D ,5 1 1,5 2 O.D.

11 How to measure patient doses at X-Rays? X-Ray beam dose: Dose-Area Product <Gy x m 2 > Measure radiation that goes out from the X-Ray unit Indirect estimation of the absorbed dose and related risk It s not fully additive ( Barium swallow + Enema + Lumbar Rg + Head CT...) Not the best unit, but very easy to measure DAP-meter Almost impossible to be used for a realistic evaluation of the Effective Dose Reference for fluoroscopy and whole-procedure doses!!! Includes beam that runs outside the body contour (not suitable for the majority of plain X-Rays)

12 How to measure patient doses at X-Rays? We can calculate the Incident dose (Gray <Gy>) using the Dose-Area Product <Gy x m 2 >

13 How to measure patient doses at X-Rays? We can calculate the Incident dose (Gray <Gy>) using the Dose-Area Product <Gy x m 2 > Can we?...

14 How to measure patient doses at X-Rays? We can calculate the Incident dose (Gray <Gy>) using the Dose-Area Product <Gy x m 2 > Can we?... No, we can t!

15 How to measure patient doses at X-Rays? We can calculate the Incident dose (Gray <Gy>) using the Dose-Area Product <Gy x m 2 > Can we?... No, we can t! Why?

16 DAP METER, ugy y = 0,8117x R 2 = 0, TLD, ugy 1.a. The DAP-meter measures 20% less than TLDs! -Why?

17 Dosis TLD (ugy) / in the air y = 0,7903x R 2 = 0, Dosis TLD (ugy) / on water phantom 1.b. Because back-scatter adds to dose 20%! 20x20 cm field; 20 cm thick water phantom / paper box air phantom Measurements at various KV and mas values

18 1.c. The back-scatter is also highly dependent on: Beam size Body segment size (thickness) To be further evaluated

19 2. Errors in real measurements Measuring errors: ± 1 cm Focus-patient dist. < FFD (up to 30% less) Cassette / X-Ray beam concordance up to ±3 x ±3 cm (as accepted by technical standards) Light / X-Ray beam concordance ±2 x ±2 cm (as accepted by technical standards) Measuring the light area in the plane of the incident central ray is not feasible in practice 1 cm error around a 24x30 cm field Error 15%

20 Evaluation of TLD measurements A range of X-ray units and a 20 cm water phantom were used

21 Evaluation of TLD measurements 4 TLDs exposed together in various conditions Standard Deviations at TLDs measurements Standard deviation (%) Measured doses (ugy)

22 Evaluation of TLD measurements TLDs compared with Ionization Chamber (all data) y = 0,9683x R 2 = 0, TLD, ugy Toate masuratorile 2000 Linear (Toate masuratorile) IC, ugy

23 Evaluation of TLD measurements TLDs compared with Ionization Chamber (all data) TLD, ugy 6000 TELEDIAGNOST 4000 POLYMOBIL 2 PRACTIX 100 PLUS TOSHIBA TOSHIBA 80 DIAGNOMAX DENTAR 0 0, , , , , , ,00 IC, ugy

24 Evaluation of TLD measurements TLDs compared with Ionization Chamber (all data) Log Axis y = 0,9683x R 2 = 0, TLD, ugy 100 Toate masuratorile 10 Linear (Toate masuratorile) IC, ugy

25 Evaluation of TLD measurements TLDs compared with Ionization Chamber (all data) Log Axis TLD, ugy TELEDIAGNOST 100 POLYMOBIL 2 PRACTIX 100 PLUS TOSHIBA TOSHIBA 80 DIAGNOMAX DENTAR 1 1,00 10,00 100, , , ,00 IC, ugy

26 Plan a strategy for patient-dose recording 1. Have a Radiology Information System (RIS) Computers, Network Software for patient data (and compliant software-support) Integrated into the Hospital Information System (HIS) To easy get patient data Be sure that the information is given at the relevant levels 2. Have a collaboration with a dosimetry body

27 Plan a strategy for patient-dose recording 3. For every X-Ray unit, every type of radiography and every size of patient (that means for all exposures in your practice during a period of time) Input into the RIS the exposure parameters Use a TLD to measure the incident dose. Let your specialised partner to process the TLDs and find the doses.

28 Plan a strategy for patient-dose recording 4. Input the measured doses into the RIS, linked with the specific X-Ray units, size of patients, type of radiograph and exposure conditions. 5. Now-on, the doses will be directly assigned to each exposure by the RIS, and also transferred in the patient file and practice statistics/reports.

29 Plan a strategy for patient-dose recording 6. Schedule new TLD measurements from time to time and in case of new technology acquisitions (X-Ray units, Screens / Detectors, ) or other changes in the practice.

30 Plan a strategy for patient-dose recording 7. Collaborate with your dosimetry partner, in scientific projects, to determine the most correct estimations of the Effective Dose, for each Incident Dose already recorded into the RIS for each type of radiography.

31 Take-Home Messages For Plain X-Rays use TLDs DAP meters are good for fluoroscopic procedures, not for radiography The doses cannot be measured for every exposure Instead, assign the dose values to exposure parameters and let the RIS do the records

ESTIMATING POPULATION DOSES FROM MEDICAL RADIOLOGY

ESTIMATING POPULATION DOSES FROM MEDICAL RADIOLOGY B. Wall, (Co-ordinator) 1, D. Hart 1, H. Mol 2, A. Lecluyse 2, A. Aroua 3, P. Trueb 3, J. Griebel 4, E. Nekolla 4, P. Gron 5, H. Waltenburg 5, H. Beauvais-March