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
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.
Some Basic Knowlege ugy (TL D) 12000 10000 8000 6000 4000 2000 0 0 50 100 150 200 250 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
ugy (TL D) Some Basic Knowlege 4500 4000 3500 3000 2500 2000 1500 1000 500 0 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 = 0,9993 30 40 50 60 70 80 90 100 110 120 130 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
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
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
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!!!
X-Ray Doses 100.000 10.000 ugy (Log scale!) 1.000 Reference doses 100 10 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)
X-Ray Doses 100.000 10.000 ugy (Log scale!) 1.000 Reference doses Median / Achievable doses HF X-ray units Tw o-pulses monophasic unit 100 10 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)
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) 700 10000 ugy 600 500 400 300 R 2 = 0,9694 ugy 8000 6000 4000 R 2 = 0,9708 200 2000 100 0 0 0 2 4 6 O.D. -2000 0 0,5 1 1,5 2 O.D.
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)
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 >
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?...
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!
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?
5000 4000 DAP METER, ugy 3000 2000 y = 0,8117x R 2 = 0,9846 1000 0 0 1000 2000 3000 4000 5000 TLD, ugy 1.a. The DAP-meter measures 20% less than TLDs! -Why?
12000 10000 Dosis TLD (ugy) / in the air 8000 6000 4000 y = 0,7903x R 2 = 0,9995 2000 0 0 2000 4000 6000 8000 10000 12000 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
1.c. The back-scatter is also highly dependent on: Beam size Body segment size (thickness) To be further evaluated
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%
Evaluation of TLD measurements A range of X-ray units and a 20 cm water phantom were used
Evaluation of TLD measurements 4 TLDs exposed together in various conditions Standard Deviations at TLDs measurements 9 8 7 Standard deviation (%) 6 5 4 3 2 1 0 0 2.000 4.000 6.000 8.000 10.000 12.000 14.000 16.000 18.000 20.000 Measured doses (ugy)
Evaluation of TLD measurements TLDs compared with Ionization Chamber (all data) 12000 y = 0,9683x R 2 = 0,977 10000 8000 TLD, ugy 6000 4000 Toate masuratorile 2000 Linear (Toate masuratorile) 0 0 2000 4000 6000 8000 10000 12000 IC, ugy
Evaluation of TLD measurements TLDs compared with Ionization Chamber (all data) 12000 10000 8000 TLD, ugy 6000 TELEDIAGNOST 4000 POLYMOBIL 2 PRACTIX 100 PLUS TOSHIBA 30 2000 TOSHIBA 80 DIAGNOMAX DENTAR 0 0,00 2000,00 4000,00 6000,00 8000,00 10000,00 12000,00 IC, ugy
Evaluation of TLD measurements TLDs compared with Ionization Chamber (all data) Log Axis 100000 y = 0,9683x R 2 = 0,977 10000 1000 TLD, ugy 100 Toate masuratorile 10 Linear (Toate masuratorile) 1 1 10 100 1000 10000 100000 IC, ugy
Evaluation of TLD measurements TLDs compared with Ionization Chamber (all data) Log Axis 100000 10000 1000 TLD, ugy TELEDIAGNOST 100 POLYMOBIL 2 PRACTIX 100 PLUS TOSHIBA 30 10 TOSHIBA 80 DIAGNOMAX DENTAR 1 1,00 10,00 100,00 1000,00 10000,00 100000,00 IC, ugy
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
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.
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.
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.
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.
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