Worldwide Quality Assurance networks for radiotherapy dosimetry Joanna Izewska Dosimetry and Medical Radiation Physics Section dosimetry@iaea.org
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
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
IAEA/WHO TLD postal dose audits 1969 - start of the service for hospitals 1981 - service available to SSDLs 1996 - 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 1997 - service offered to Central and Eastern European countries 500 beam checks per year
QA of the IAEA TLD system,, 1997-2003 Reference irradiations by BIPM and PSDLs: n = 116 (Co-60 and X-rays) mean D TLD /D stat = 1.001 SD = 0.8% Comparisons with TLD networks and reference centres: n = 260 (Co-60 and X-rays) mean D TLD /D stat = 1.001 SD = 1.1%
1.05 1.04 1.03 Reference irradiations, BIPM and PSDLs, 1997-2003 D IAEA /D PSDL 1.02 1.01 1.00 0.99 0.98 0.97 BIPM BEV PTB Co-60 PTB X-rays ARPANSA OMH NPL Co-60 NPL X-rays NRC 0.96 0.95 1997 1998 1999 2000 2001 2002 2003 Year
Reference irradiations: TLD networks and reference centres 1997-2003 1.05 1.04 1.03 1.02 1.01 D TLD /D stat 1.00 0.99 0.98 0.97 0.96 0.95 Co-60 beams X-rays 1997 1998 1999 2000 2001 2002 2003 Year
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 1997-2003: 587 beam checks: mean = 1.006, SD = 1.9%, min = 0.88, max = 1.13 96% results within 3.5% acceptance limit before correction, 100% poor results corrected
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
Number of beams checked per region EM 10% AF 3% WP 21% EU 16% Years 1969-2003 115 countries 1339 hospitals 5163 audits SE 14% AM 36%
1.8 1.6 TLD audits, hospitals: 1969-2003 ( 60 Co and X-rays) 115 countries 1339 hospitals 5163 audits 1.4 D TLD /D stat 1.2 1.0 0.8 ±5% 0.6 0.4 1970 1975 1980 1985 1990 1995 2000 Year
IAEA/WHO TLD audits for hospitals, 1969-200 2003 5163 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, 2000-2003 1543 beams audited: 841 Co-60 beams 702 high energy X-ray beams mean = 1.008, SD = 7.6% Results within 5% limit: 86%
TLD results for new hospitals 1997-200 2003 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 500 400 300 200 100 0 regular participation new hospitals 1998 1999 2000 2001 2002 2003 year
Deviations in TLD audits, 2002-2003 2003 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 %
IAEA/WHO TLD service, 1998-2002 Type of ionisation chambers obsolete 8% local make 5% 0.1-0.3 cc 14% Distribution of TLD results: mean, standard deviation (SD) 1.06 73% Farmer 0.6 cc Data reported in 958 data sheets. mean D TLD /D stat 1.04 1.02 1.00 0.98 0.96 SD 0.1-0.3 cc 0.6 cc obsolete local ion chamber model
Deviations outside 5% limit: 2002 2003 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
IAEA/WHO TLD results within 5% limit Fraction of results within 5% limit 1.0 0.9 0.8 0.7 0.6 after follow-up 0.5 1st check 0.4 1992 1994 1996 1998 2000 2002 Year
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
IAEA expert missions, example 1 3 EXPERT SSDL EXPERT 2 EXPERT Mission findings: problems with basic dosimetry Reasons: unreliable dosimeters, poor training, staff rotation
However, TLD is not everything Co-60 output 1.100 1.000 0.900 0.800 0.700 0.600 Errors in treatment time calculation with home-made software 1 st TLD 0 200 400 600 800 1000 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
TLD audits in Central and Eastern Europe 1997-2003 Radiotherapy infrastructure (DIRAC): 28 countries, 378 hospitals, 675 RT units Participants in the IAEA TLD audits, 1997-2003: 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
TLD audits in Central and Eastern Europe IAEA audits 1997-2003 22 countries RUS 180 190 hospitals 372 RT machines 687 beam checks HUN hospitals audits LIT SLR UKR 160 140 120 100 80 60 40 20 number of hospials/audits 0 5 10 15 20 0 country no.
Distribution of TLD results, 1997-2003 Distribution parameter Number of audits Eastern Europe Other regions All regions 687 1658 2345 Mean 1.006 1.011 1.010 Std. deviation 0.084 0.075 0.077 Fraction within 5% limit 0.82 0.85 0.84
TLD results for hospitals C.- E. Europe, 1997-2003 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
Follow-up of poor results, C.-E. Europe, 1997-2003 Percentage of TLD results within the 5% limit average after correction 100% 92% average before correction 82% A B C
TLD results vs. dosimetry equipment, Central and Eastern Europe, 2000-2003 2003 Number of audits (percentage) Farmer 0.6 cc 0.1 0.3 cc obsolete 257 (49%) 83 (16%) 55 (11%) no equipment reported 122 (24%) Mean 1.004 1.006 1.043 1.017 Standard deviation 0.034 0.038 0.076 0.064
TLD results vs. dosimetry protocols Central and Eastern Europe, 2000-2003 2003 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 1.006 1.003 1.043 1.025 Standard deviation 0.032 0.029 0.076 0.074
Frequency Age of radiotherapy units in Eastern Europe, countries with poor results 20 18 16 14 12 10 8 6 4 2 0 Data from DIRAC 0 4 8 12 16 20 24 28 32 36 40 machine age, years n =136 mean = 16 years min = 2 years max = 37 years
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
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
Cumulative number of beam checks, EQUAL 1200 220 200 1100 180 160 1000 900 number of beams 140 120 100 80 Follow-up 2 nd checks number of beams 800 700 600 500 400 60 40 20 0 1998 1999 2000 2001 2002 time [x2 months] All beams checked 1998 1999 2000 2001 2002 All beams checked (total of 2204 beams) 300 200 100 photon (1146 beams) electron (778 beams) photon with MLC (76 beams) 0 1998 1999 2000 2001 2002 time [x2 months] Data presented in the IAEA Symposium Nov. 2002
Radiological Physics Center (RPC) Set up in 1968 1300 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
1400 RPC audit results TLD audits for photon beams, year 2000 Number of measurements 1200 1000 800 600 400 PHOTON DATA χ = 1.008 S D = 1.8% n = 5177 (number of measurements) TLD output checks: results within 5% limit photons: 97% electrons: 95% 200 After correction: 98% 0 0.93 0.94 0.95 0.96 0.97 0.98 0.99 1 1.01 1.02 1.03 1.04 1.05 1.06 1.07 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
National External Audit Group (EAG) supported by National Authority Med. Phys. Group TLD Meas. Lab IAEA SSDL EAG Local RT hospitals
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.
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
TLD network of Argentina Set up of EAG in 1996 90 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
TLD network of Brazil Set up of EAG (NCI) in 1999 33/170 hospitals: 36 Co-60 units, 33 linacs Distribution of the results (reference conditions) TLD run beams < 3% 3-5% 5-10% >10% 1 70 77.1 7.1 10.0 5.7 2 60 83.3 15.0 1.7 0 3 68 79.4 19.1 1.5 0 4 67 74.6 25.4 0 0 Data presented in the IAEA Symposium Nov. 2002
frequency TLD programme in Poland Set up of the audit programme in 1991 21 hospitals: 21 Co-60 units, 43 linacs 40 35 30 25 20 15 10 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% 5 0-10 -8-6 -4-2 0 2 4 6 8 10 deviations [%] linac electrons N = 44 m =0.5% SD = 2.4% Data presented in the IAEA Symposium Nov. 2002
Poland, TLD nonn on-ref. conditions, Co-60 60,, 2004 deviation, % 5 3 1-1 -3-5 0 2 4 6 8 10 centre code 10x10/d=10cm 10x10/d=20cm 8x8/d=10cm 10x20/d=10cm 10wx10/d=10cm
Poland, TLD nonn on-ref. conditions, HE X-rays, X 2004 5 deviation, % 3 1-1 -3 10x10/10 10x10/5 8x8/10 10x20/10 10wx20/10-5 0 2 4 6 8 10 12 14 16 18 20 22 centre code
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 ).
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)
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.
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)
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
Dosimetry audits are recommended for all radiotherapy centres (IAEA Basic Safety Standards) and become mandatory in several countries (Euratom 97/43)