IAEA code of practice for dosimetry in diagnostic radiology: recommendations for hospitals and specific issues

Transcription

1 IAEA code of practice for dosimetry in diagnostic radiology: recommendations for hospitals and specific issues Antti Kosunen Radiation Metrology Laboratory-STUK Radiation safety and dosimetry in medical applications May 2012 TTÜ, Ehitajate tee 5, Tallinn, Estonia RADIATION AND NUCLEAR SAFETY AUTHORITY Presentation Review /introduction to contents of IAEA TRS 457 for clinical dosimetry Experiences of use the IAEA TRS 457 (KAP meters, others) Remarks based on work at the SSDL of STUK Methods by TLD are not reviewed RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 2 1

2 RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 3 IAEA TRS 457, Clinical dosimetry Dosimetry formalism Dosimetry intrumentation Quantities and uncertainties General radiography Fluoroscopy Mammography Computed tomography Dental radiography RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 4 2

3 IAEA TRS 457, Clinical dosimetry Dosimetry phantom patient Guidance for selection of patients for DRL Appendix VI. Application of patient dose measurements Background Guidance for DRLs Guidance for organ dose conversion factors for examinations Summary of using effective dose RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 5 IAEA TRS 457, Clinical dosimetry Assumed that the x- ray equipment is properly maintained according to QA program Assumed that the x ray tube output is linear relative to tube loading, if not complementary measurements are required HVL For interpolations of calibration coefficients For conversions to organ doses (mammography) Not necessrerily for every dose measurement, as information from Quality Control results exist RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 6 3

4 IAEA TRS 457, Clinical dosimetry Examples and worksheets for measurements Dosimeters should be calibrated at the laboratory Calibration interval: Based on national requirements, Usually should not exceed two years RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 7 IAEA TRS 457, Accuracy requirements for dosimetry At reference conditions of dosimetry Risk assessment : Absolute risk Dose surveys Relative risk Interventional procedures Quality assurance measurements Paediatric procedures ( 2sd ) ~20 % 7 % RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 8 4

5 IAEA TRS 457, Dosimetry formalism Air kerma based formalism Beam quality correction factor RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 9 IAEA TRS 457, Selection of instruments, clinical Requirements of International Standards are followed: Requirements for dosemeters at laboratory can be used also as a background information for clinical dosemeters RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 10 5

6 IAEA TRS 457, Measurement uncertainty (accuracy) RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 11 IAEA TRS 457, General radiology, dosimetry quantities RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 12 6

7 IAEA TRS 457, General radiology Incident air kerma Air kerma detector with isotropic response RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 13 IAEA TRS 457, General radiology, phantoms RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 14 7

8 IAEA TRS 457, Review on phantoms RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 15 IAEA TRS 457, General radiology, uncertainty RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 16 8

9 IAEA TRS 457, Fluoroscopy, dosimetry quantities RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 17 IAEA TRS 457, Fluoroscopy Detector with back scatter measurement capability Anti- scatter grid in position if used Focus to table top distance as used clinically Phantom 20 cm, 30 cm for large patients Collimation large, to phantom size Exposure under ABC RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 18 9

10 IAEA TRS 457, Fluoroscopy RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 19 IAEA TRS 457, Fluoroscopy, uncertainties RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 20 10

11 IAEA TRS 457, Fluoroscopy, kerma -area product (P KA ) Calibration of KAP meters in situ Beam area method Tandem method with reference KAP meter Toroi et.al. A tandem calibration method for kerma-area product meters, PMB 53, 2008 RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 21 IAEA TRS 457, Kerma -area product Incident beam KAP meter Transmitted beam 5 mmal total filtration Toroi et.al. Effects of radiation quality on the calibration of kerma-area product meters in x-ray beams, PMB 53, 2008 RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 22 11

12 IAEA TRS 457, Fluoroscopy, Kerma area- product Over and under couch set-ups Beam area or tandem method RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 23 IAEA TRS 457, KAP -meters Toroi et.al. Effects of radiation quality on the calibration of kerma-area product meters in x-ray beams, PMB 53, 2008 RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 24 12

13 IAEA TRS 457, Kerma -area product (KAP) RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 25 IAEA TRS 457, KAP-meters Large fields for reference KAP meter 30 cm * 30 cm Patient Dose Calibrator PDC-1 Radcal kv Toroi & Kosunen. The energy dependence of the response of a patient dose calibrator, PMB 54, 2009 RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 26 13

14 KAP-meters, Set-up 80 kv, 4.8 mmal, 10*10cm at 30 FDD Toroi et.al. Calibration of kerma area product meters with a patient dose calibrator, IDOS proceedings, Vol2, IAEA, Standards-Applications-and-Quality-Assurance-in-Medical-Radiation-Dosimetry-IDOS- Proceedings-of-an-International-Symposium-Vienna-9-12-November-2010 RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 27 IAEA TRS 457, KAP uncertainties IEC 60580, 25 % (k=2) In examinations with varying voltage, 25 % For specific tube voltage and energy dependence considered: 6 % (k=2) KAP indicators based on calculations need to be calibrated also RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 28 14

15 IAEA TRS 457, Mammography, dosimetry quantities RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 29 IAEA TRS 457, Mammography Plane parallel IC with entrance window (low energy dependence) 45 mm PMMA phantom RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 30 15

16 IAEA TRS 457, Mammography, HVL HVL measurement RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 31 IAEA TRS 457, Mammography, glandular dose RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 32 16

17 IAEA TRS 457, Mammography, uncertainties RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 33 IAEA TRS 457, Computed tomography, dosimetry quantities RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 34 17

18 IAEA TRS 457, Computed tomography CT air kerma indices In air or in a phantom T, Nominal slice thickness N, number of slices/detector rows per scan for MSCT/MDCT RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 35 IAEA TRS 457, Computed tomography, phantoms RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 36 18

19 IAEA TRS 457, Dosimetry formalism RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 37 IAEA TRS 457, Computed tomography RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 38 19

20 IAEA TRS 457, Computed tomography Air kerma lenght product RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 39 IAEA TRS 457, Computed tomography, kerma lenght product RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 40 20

21 AAPM, IAEA, Recent approach for wide CT beam dosimetry Work by ICRU? RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 41 IAEA HHS No5, Computed tomography From :IAEA Human Health Report No:5, Status of computed tomography dosimetry for wide cone beam scanners, 2011 RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 42 21

22 Computed tomography, kerma lenght product, STUK approach Measurement of kerma lenght product for whole examination RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 43 IAEA TRS 457, Dental radiography, dosimetry quantities RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 44 22

23 IAEA TRS 457, Dental radiography TRS include quidance for bitewiew and panoramic examinations Uncertainties Kerma lenght product 13 % - 6 % Kerma area product 13,2 % 6,4 % RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 45 IAEA TRS 457, Implementation and testing Advanced techniques, The development of advanced dosimetry techniques for diagnostic and interventional radiology Coordinated Research Project on Implementation of the International Code of Practice on Dosimetry in Diagnostic Radiology TRS 457 RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 46 23

24 IAEA TRS 457, Implementation and testing Advanced techniques, Paediatrics - clinical Development of guidance General Radiography fluoroscopy CT analysis & uncertainty Interpretation of clinical data Development of guidance development of questionnaire organ dose + eff. Dose & risk SSDL Preparation for intercomparison intercomparison -SSDL - KLP intercomparison -SSDL - KAP new qualities [KAP & mammo] Farmer chambers with RQT I/II RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 47 IAEA TRS 457, Implementation and testing Advanced techniques, Advanced dosimetry Development of guidance MDCT cone beam CT vs CT mammographic tomosynthesis dental dosimetry Skin dose Development of guidance Film characterisation SSDL high dose calibration high dose patients low dose calibration low dose patients uncertainty DICOM Development of guidance survey of DICOM capability Uncertainty formulation Assessment of clinical scenarios assessment of uncertainty budget from scenarios Development of guidance I/II RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 48 24

25 Summary I/II IAEA TRS 457 contains a comprehensive description of dosimetry methods used for diagnostic radiology Two options for reference KAP are presented; beam area or use of a reference KAP meter Generally % (k=2) level of uncertainty (KAP meters 25 %) can be achieved for measurements in clinical dosimetry. Accuracy below 10% requires use of reference class dosemeters and/or calibration of dosemeter for user specific radiation qualities. RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 49 Summary II/II For dosimetry of wide beam CT the IAEA TRS457 methods need to be complemented by more recent dosimetry guidance (AAPM, IAEA, others) IAEA TRS 457 has limitations for wide beam CT dosimetry. More recent recommendations exist; AAPM (2010), IAEA (2011) Advanced dosimetry techniques for diagnostic and interventional radiology are under investigation in the coordinated research project by IAEA. RADIATION AND NUCLEAR SAFETY AUTHORITY / AK-STUK 50 25