Worldwide Quality Assurance networks for radiotherapy dosimetry

Transcription

1 Worldwide Quality Assurance networks for radiotherapy dosimetry Joanna Izewska Dosimetry and Medical Radiation Physics Section

2 Audit in radiotherapy dosimetry Objectives to enhance confidence in accuracy of clinical dosimetry to ensure that QA procedures are adequate to ensure that equipment works as expected On-site audits (limited number of hospitals) QA programmes, mechanical checks, safety, dosimetry, TPS, clinical records Postal audits (large scale) spot checks of one or a few beam parameters

3 Dosimetry audit networks Dosimetry audit networks Major TLD audit networks: IAEA/WHO: 115 countries, 1350 hospitals EQUAL/ESTRO: mainly EU countries, 500 hospitals RPC/MDACC: mainly USA and Canada, 1300 hospitals Clinical trials ( e.g. EORTC, RTOG, MRC) National audits (mailed, on-site) single dose comparisons (e.g. Belgium, the Netherlands, Sweden, Switzerland) regular audit programmes (e.g. Finland, Germany, New Zealand, UK) IAEA supported national audit networks (18 countries) Approx. 60% of hospitals worldwide participate in audits

4 IAEA/WHO TLD postal dose audits start of the service for hospitals service available to SSDLs follow-up TLD when deviations outside the 5% acceptance limit are detected Follow-up on-site visits by national SSDLs or IAEA experts when deviations persist service offered to Central and Eastern European countries 500 beam checks per year

5 QA of the IAEA TLD system,, Reference irradiations by BIPM and PSDLs: n = 116 (Co-60 and X-rays) mean D TLD /D stat = SD = 0.8% Comparisons with TLD networks and reference centres: n = 260 (Co-60 and X-rays) mean D TLD /D stat = SD = 1.1%

6 Reference irradiations, BIPM and PSDLs, D IAEA /D PSDL BIPM BEV PTB Co-60 PTB X-rays ARPANSA OMH NPL Co-60 NPL X-rays NRC Year

7 Reference irradiations: TLD networks and reference centres D TLD /D stat Co-60 beams X-rays Year

8 IAEA TLD audits for SSDLs Organisation: 80 beam checks per year (56 SSDLs out of 73) 2 irradiation runs per year follow-up TLD for deviations larger than 3.5% acceptance limit Results : 587 beam checks: mean = 1.006, SD = 1.9%, min = 0.88, max = % results within 3.5% acceptance limit before correction, 100% poor results corrected

9 TLD based audit networks for radiotherapy dosimetry Country participating in the IAEA/WHO TLD service National QA network or participant in international network other than IAEA QA network co-operating with IAEA Country not having radiotherapy or not participating in an audit network

10 Number of beams checked per region EM 10% AF 3% WP 21% EU 16% Years countries 1339 hospitals 5163 audits SE 14% AM 36%

11 TLD audits, hospitals: ( 60 Co and X-rays) 115 countries 1339 hospitals 5163 audits 1.4 D TLD /D stat ±5% Year

12 IAEA/WHO TLD audits for hospitals, beams audited: 3941 Co-60 beams 1222 high energy X-ray beams mean = 1.012, SD = 8.3% Results within 5% limit: 77% TLD results, beams audited: 841 Co-60 beams 702 high energy X-ray beams mean = 1.008, SD = 7.6% Results within 5% limit: 86%

13 TLD results for new hospitals New hospitals N=941,m=1.014 SD=0.081 (dev. within 5%): 77% (dev.>10%): 9% Regular participation N = 1404 beams m=1.007 SD=0.075 (dev. within 5%): 89% (dev.>10%): 5% nr of beams checked regular participation new hospitals year

14 Deviations in TLD audits, misadministration? 1% 6% accident? 9% tolerance accident? 0.5% misadministration? 2% tolerance 5% 84% within requirement 92% within requirement Co-60 units 409 beams checked 67 deviations beyond 5 % (within 5%) (dev. 5-10%) (dev.10-20%) (dev. > 20%) Medical accelerators 425 beams checked 31 deviations beyond 5 %

15 IAEA/WHO TLD service, Type of ionisation chambers obsolete 8% local make 5% cc 14% Distribution of TLD results: mean, standard deviation (SD) % Farmer 0.6 cc Data reported in 958 data sheets. mean D TLD /D stat SD cc 0.6 cc obsolete local ion chamber model

16 Deviations outside 5% limit: unknown 27% 8% errors in PDD/TMR other reasons 12% 0% calibration in plastic 28% errors in X/D conversion 2% confusion of N D,air and N D.w 23% SSD/SAD setup errors

17 IAEA/WHO TLD results within 5% limit Fraction of results within 5% limit after follow-up 0.5 1st check Year

18 IAEA expert missions The IAEA dosimetry travel kit used for expert missions to radiotherapy hospitals Reasons for problems identified in radiotherapy dosimetry are traced, explained, corrected and reported

19 IAEA expert missions, example 1 3 EXPERT SSDL EXPERT 2 EXPERT Mission findings: problems with basic dosimetry Reasons: unreliable dosimeters, poor training, staff rotation

20 However, TLD is not everything Co-60 output Errors in treatment time calculation with home-made software 1 st TLD days 2 nd TLD actual software expert IAEA expert discovered a problem >300 patients, treated with Co-60, affected IAEA mission recommendations on staff training

21 TLD audits in Central and Eastern Europe Radiotherapy infrastructure (DIRAC): 28 countries, 378 hospitals, 675 RT units Participants in the IAEA TLD audits, : 22 countries, 190 hospitals, 372 RT units National QA networks: BUL*, CZR, POL, ROM*, UKR* audits offered to ~90 hospitals, approx. 170 RT units 75% HOSPITALS PARTICIPATE IN TLD AUDITS *under development

22 TLD audits in Central and Eastern Europe IAEA audits countries RUS hospitals 372 RT machines 687 beam checks HUN hospitals audits LIT SLR UKR number of hospials/audits country no.

23 Distribution of TLD results, Distribution parameter Number of audits Eastern Europe Other regions All regions Mean Std. deviation Fraction within 5% limit

24 TLD results for hospitals C.- E. Europe, On average 82% TLD results within the acceptance limit of 5% Great variability of results for among countries A. 10 countries: 95%-100% acceptable results B. 6 countries: above average 83%-94% acceptable results C. 6 countries: poor results below the 82% average

25 Follow-up of poor results, C.-E. Europe, Percentage of TLD results within the 5% limit average after correction 100% 92% average before correction 82% A B C

26 TLD results vs. dosimetry equipment, Central and Eastern Europe, Number of audits (percentage) Farmer 0.6 cc cc obsolete 257 (49%) 83 (16%) 55 (11%) no equipment reported 122 (24%) Mean Standard deviation

27 TLD results vs. dosimetry protocols Central and Eastern Europe, N D,w - based N K - based old N X - based unknown Number of audits (percentage) 140 (35%) 162 (41%) 24 (6%) 69 (18%) Mean Standard deviation

28 Frequency Age of radiotherapy units in Eastern Europe, countries with poor results Data from DIRAC machine age, years n =136 mean = 16 years min = 2 years max = 37 years

29 Summary: Central & Eastern Europe Better TLD results for regular participation (77% acceptable results in 1 st participation, 89% acceptable results in 2 nd participation or next ) TLD results in Central and Eastern Europe are variable (10 countries have excellent results; 6 countries have good results; 6 countries have poor results). Major investment in equipment and training is necessary in countries with poor results to reach the level of other countries

30 EQUAL/ESTRO TLD network Set up in 1998 by ESTRO 500 hospitals of European Union (>50%) Programme: output checks for high energy photon and electron beams audit of beam parameters in non-reference conditions audit for photons with MLC Results: 98% of the output checks are within 5% limit 2nd check performed in 10% of the participating centres, because a deviation larger than 5% was observed in at least one of the beam parameters in nonreference conditions. Data presented in the IAEA Symposium Nov. 2002

31 Cumulative number of beam checks, EQUAL number of beams Follow-up 2 nd checks number of beams time [x2 months] All beams checked All beams checked (total of 2204 beams) photon (1146 beams) electron (778 beams) photon with MLC (76 beams) time [x2 months] Data presented in the IAEA Symposium Nov. 2002

32 Radiological Physics Center (RPC) Set up in hospitals mainly in USA and Canada Audit programme: On-site dosimetry reviews by RPC physicists Remote tools: TLD checks for photons and electrons, review of dosimetry data, treatment records of patients, QA programme, mailable anthropomorphic phantoms for special treatment techniques Data presented in the IAEA Symposium Nov. 2002

33 1400 RPC audit results TLD audits for photon beams, year 2000 Number of measurements PHOTON DATA χ = S D = 1.8% n = 5177 (number of measurements) TLD output checks: results within 5% limit photons: 97% electrons: 95% 200 After correction: 98% TLD to INST On-site visits: 80% of institutions visited receive recommendations to improve their QA programs Data presented in the IAEA Symposium Nov. 2002

34 National External Audit Group (EAG) supported by National Authority Med. Phys. Group TLD Meas. Lab IAEA SSDL EAG Local RT hospitals

35 Steps in national TLD audits STEP 1. Beam output in reference conditions, high energy photons STEP 2. dose in reference conditions and in nonreference conditions on-axis a) High energy photons b) High energy energy electron beams, at z max STEP 3. Dose in reference conditions and in nonreference conditions off-axis for open and wedged fields, high energy photons Part 1. symmetric fields Part 2. asymmetric fields.

36 Step 3: non-reference conditions, high energy photons, symmetric fields 3 TLDs 5 cm 10 cm 5 cm 1. 2 TLDs: 10 x 10 cm 2 on-axis open 2. 3 TLDs: 20 x 20 cm 2 profile X, open 3. 3 TLDs: 20 x 20 cm 2 profile Y, open 4. 3 TLDs: 20 x 20 cm 2 profile X, wedged SSD or SAD setup TOTAL: 11 TLDs per beam Steps 1-4: deliver 2 Gy to TLD on axis

37 TLD network of Argentina Set up of EAG in hospitals: 69 Co-60 units, 42 linacs Audit programme: Photons, reference conditions Photons, non-reference conditions Results till 2003, reference conditions 90%-98% results within 5% limit for Co-60, 98%-100% for high energy x-rays since 1999 no deviations > 10% Non-ref conditions 81%-93% results within 5% limit Data presented in the IAEA Symposium Nov. 2002

38 TLD network of Brazil Set up of EAG (NCI) in /170 hospitals: 36 Co-60 units, 33 linacs Distribution of the results (reference conditions) TLD run beams < 3% 3-5% 5-10% >10% Data presented in the IAEA Symposium Nov. 2002

39 frequency TLD programme in Poland Set up of the audit programme in hospitals: 21 Co-60 units, 43 linacs Co-60 linac photons linac electrons Co-60 beams N = 55 m =0.5% SD = 2.4% linac photons N = 52 m =-0.9% SD = 2.8% deviations [%] linac electrons N = 44 m =0.5% SD = 2.4% Data presented in the IAEA Symposium Nov. 2002

40 Poland, TLD nonn on-ref. conditions, Co-60 60,, 2004 deviation, % centre code 10x10/d=10cm 10x10/d=20cm 8x8/d=10cm 10x20/d=10cm 10wx10/d=10cm

41 Poland, TLD nonn on-ref. conditions, HE X-rays, X deviation, % x10/10 10x10/5 8x8/10 10x20/10 10wx20/ centre code

42 Summary: national EAGs National audit systems are an effective means in verifying dosimetry at hospitals easier access to a regular audit for a hospital rapid problem resolution. IAEA has supported several national TLD audit systems and disseminated the methodology to a number of countries. Further development of national audit systems is necessary to respond to the needs (only 40% of local hospitals have participated by 2002 ).

43 Other dosimetry audit systems Finland, New Zealand On-site audits by the regulatory body, mandatory UK network Round robin runs with solid phantom Czech Republic TLD alternated with on-site visits, mandatory Clinical audit in preparation Audits for clinical trials various phantoms depending on the needs own programme or checks through existing networks (e.g. RPC)

44 Summary: all networks Approx. 60% of radiotherapy hospitals worldwide participate in an external audit. Audits in developing countries show lower percentage of results within the acceptance limits, particularly for the first participation. The results of beam output checks are satisfactory in industrialised countries, although deviations in non-reference conditions have been observed.

45 Trends in dosimetry audits Development of audit methodology for modern technology in radiotherapy MLC on-axis by EQUAL/ESTRO IMRT checks by RPC/Houston TLD and radiochromic film H&N phantom filled with 3D gel dosimeter IAEA TLD holder with horizontal arm Postal audits for brachytherapy (EQUAL)

46 Conclusion Regular participation in external audits is vital for a radiotherapy department Dosimetry audit should be carried out in non-reference conditions, as well as in the reference conditions Investment in equipment and training is necessary for developing countries to reach the level of industrialised countries

47 Dosimetry audits are recommended for all radiotherapy centres (IAEA Basic Safety Standards) and become mandatory in several countries (Euratom 97/43)