Presented by: Rebecca M. Howell PhD, DABR, FAAPM. Results from Voluntary Independent External Peer Review of Beam Output

Transcription

1 Presented by: Rebecca M. Howell PhD, DABR, FAAPM Results from Voluntary Independent External Peer Review of Beam Output

2 What do we hope to achieve with independent peer review? Independent peer review is an important tool for improving quality of the clinical physics program. Enhance patient safety Ensure the best possible treatment for our patients Meet regulatory requirements

3 Independent Peer Review Around the World United States MD Anderson RDS IROC-H ADCL MDADL University of Wisconsin ADCL RCL The World IAEA/WHO International Atomic Energy Agency and World Health Organization ACDS - Australian Clinical Dosimetry Service Radiotherapy Trials Quality RTTQA - Radiotherapy Quality Assurance (UK) JCOG Japan Clinical Oncology Group EORTC - European Organization for Research and Treatment of Cancer (audits by IROC-H)

4 MD Anderson Cancer Center Section of Outreach Physics Outreach Physics IROC-H RDS ADCL MDADL

5 Radiation Dosimetry Services RDS Independent Peer Review Services Beam output for external beam RT: megavoltage photon (2-25 MV) electron (4-20 MeV) orthovoltage (1.9 mm Al - 3 mm Cu HVL) Cobalt-60 Dose verification for special procedures: total body dosimetry total skin dosimetry Absorbed Dose in Blood Irradiators Dose Verification Cell Irradiations (in development)

6 Imaging and Radiation Oncology Core Houston IROC-H Independent Peer Review Services (for clinical trial participants) Beam output for external beam RT: megavoltage photon (2-25 MV) electron (4-20 MeV) Cobalt-60 Single beam small field checks Advanced technology end-to-end testing: imaging, planning, delivery Head and neck Prostate Lung (motion phantom) SRS Spine SBRT Liver (motion and multi-target) Also available for fee through MDADL Site Visits on site review of dosimetry TPS versus IROC physicist measurements of basic dosimetry parameters (PDD, OF, WF, OAF) Mechanical evaluations (linac, IGRT, MLC) Programmatic reviews (QA program, staffing, ) Virtual Site Visits (analogous to site visit without measurements)

7 Accredited Dosimetry Calibration Laboratory ADCL AAPM Accredited Calibrations Offered Electrometers Charge and Current Scales External Beam Ionization Chambers: Co-60 Absorbed Dose to Water Co-60 Exposure/Air Kerma X-Ray (Orthovoltage) Well-Ionization Chambers: High Dose Rate (Ir-192) Low Dose Rate (Pd-103, I-125, Cs-131, Cs-137 and Ir-192) Brachytherapy Sources Low Dose Rate (Pd-103, I-125, Cs-131, Cs-137 and Ir-192) See Joint AAPM/IROC Registry for current available source models

8 EBRT Monitoring RDS versus IROC Who, What, How Often Users RDS Any institution that requests service Beams Monitored MV photon and electron, orthovoltage, blood irradiations, specials Frequency of Service Annual, biannual, quarterly, monthly, on request Users IROC Clinical trial participants Beams monitored All photon and 3 electron energies (alternating years), small field Frequency of Service Annual Note: Some institutions use RDS to supplement electron monitoring or to increase frequency of monitoring.

9 History of RDS In 1968, the Texas Regional Medical Physicists (TRMP) was formed by Dr. Shalek, to provide independent peer review. In 1974, the NCI funded the six Centers for Radiological Physics (CRP); TRMP became the Southern CRP to provide QA audit services. In 1985, when the NCI terminated the CRP contracts, Drs. Shalek and Stovall created a new for-fee service, the RDS. Dr. Stovall served as the Director of the RDS for 30 years, (65 years at MDA since 1951) I was appointed Associate Director of RDS in 2015 and promoted to Director in 2016.

10 RDS Users Since 2001 Since 2001, RDS has monitored 21,000 unique EBRT beams at > 2,000 institutions in the United States and 150 institutions

11 Current Users Frequency of Service Frequency of Service Number of Institutions Annual 1005 Quarterly 92 Monthly 12 Bi-annual 19 Semi-annual 345 By-request 799 Other 43 Total 2315 Most institutions monitor beam output on annual basis. Of the 799 institutions set-up for by-request services, 150 placed at least one order in the past year. Note: Total number of distinct institutions is 2014, 10% of institutions use different monitoring frequency for different machines/beam types.

12 Dosimeters TLD-100 (LiF:Mg,Ti) powder from Quantaflux LLC (San Jose, CA) Fully characterize each new batch Batch is named for year in which it is purchased (Currently using B14) Do not reuse Controls are irradiated weekly on 60 Co unit at the MD Anderson ADCL Full review of control irradiations every quarter.

13 Phantoms Acrylic mini-phantoms (3 TLD photon and 6TLD electron) Dimensions based on the type of beam and the energy. Electrons: sufficient for full phantom scatter. Photons: the dimensions are sufficient for electronic scatter equilibrium, but not photon scatter equilibrium. Why mini-phantoms? shipping $$ But. requires BSF to determine output in full phantom.

14 What about the Uncertainty in the TLD Dose? TLD system is calibrated based on the signal-to-dose conversion established with reference TLD irradiated in 60 Co (ADCL), with reference dose of 300 cgy. Uncertainty in the dose determination is 1.3% for TLD. This accuracy allows for a tolerance of ±5% to be used. Alvarez, Kry, Stingo, and Followill. TLD and OSLD dosimetry systems for remote audits of radiotherapy external beam calibration. Rad Meas. In press

15 Quality Assurance TLD Reading Process Measure the mass of every single TLD on high accuracy digital scales. There are 3 TLD for each measurement. SD of reading/mass is reviewed during QC Tolerance is 3%, but is typically < 1.5% Read standards during every session, which includes 24 sets of 3. Read 9 standards per session: 3 at beginning, 3 at middle, 3 at the end.

16 Quality Assurance TLD Dose Calculation Detailed review of results for each session. Any inconsistencies are investigated e.g., Institution X, has historically calibrated in muscle, but in water was reported for the current set of TLD Check the documentation from physicist physicist to confirm Modify calculation as appropriate

17 Quality Assurance TLD Dose Calculation Detailed review of results for each beam.

18 Comparison with historical results. Quality Assurance Review Historical Results

19 Results Confidentiality is a key component of participation. All results are reported in aggregate. Individual examples are anonymized.

20 Summary Statistics All EBRT Beams RDS monitored 155,237 EBRT beams Number of Reports 45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000 Average 0.999± % 85.5% 64.1% were within ± 3% 2% 1% 11.8% 20.3% 26.0% 17.8% 9.6% < 6% of beams monitored by RDS are outside of ± 3%. 5, % % 0.6% % % % % % 1.05 Dose Ratio (Measured/Expected) 0.2% % %

21 Dose Ratio (Measured/Expected) Summary Statistics All MV Photon Beams RDS monitored 52,257 MV photon beams Number of Reports 16,000 14,000 12,000 10,000 8,000 6,000 4,000 2, Average ± % % % % % % % % % 1.02 Distributed equally between positive and negative ratios 3.7% % % % %

22 Summary Statistics All Electron Beams RDS monitored 101,399 electron beams Number of Reports 25,000 20,000 15,000 10,000 Average 0.999± % 20.2% 24.5% 16.7% 9.4% Distributed somewhat more toward ratios <1.00 5, % 0.2% 0.7% 2.4% 5.5% 4.3% 1.8% 0.7% 0.3% 0.1% 0.1% Dose Ratio (Measured/Expected)

23 Comparison with IROC Results Similar Averages 1.0 with most ± 3% Electron beams Average: ± results ( 22% compare 2014) 480 beams need repeat OSLD Photon beams Average: ± results ( 29% compare 2014) 2000 # results OSLD/Institution

24 Summary Statistics All Orthovoltage Beams RDS monitored 1319 orthovoltage beams Number of Reports % 0.90 Average 0.995± % % % % % % % % % % % % % % % % % % % % 1.10 Dose Ratio (Measured/Expected)

25 Outside of Criteria Setup/documentation Issues SAD vs SSD deliver (and vv) Water vs Muscle (and vv) Wrong field size (20 x 20 vs 10 x 10) Often happens when do electrons 1 st Wrong energy For electrons trouble shoot with PDD 100 MU or 200 MU vs 300 MU And one not to worry about, I left the others in room (out of beam)

26 Beam Type Institution's Frequency of Service Outside of Criteria Real Issues Initial Description Repeated Cobalt-60 Monthly MV photon Monthly MV photon Quarterly 1.22 Physicist found a problem with timer correction factor from most recent calibration. Physicist had ion chamber recalibrated; ADCL determined chamber required repair. Physicist found an 18% error in calibration of a newly commissioned linac MV photon 6-15 MeV electrons Annual Physicist reported incorrect solid water correction factor had been applied, resulting in a 3% calibration error. Error was corrected and 18 MV photons 6-20 MeV electrons Monthly Physicist determined that mercury barometer was malfunctioning, resulting in a 4% error in calibration of a newly commissioned linac MeV electron Quarterly 1.09 Physicist found two problems; depth of dmax was incorrect due to a change in energy, and measured depth dose data did not include a correction for chamber radius. 1.02

27 Outside of Criteria Recent Scenario.. New linac Wanted beam output verification prior to 1 st patient. Rush order Notified by of results. Energy Ratio (MDA/reported) 6 MV MV MV MeV MeV MeV MeV MeV 0.93

28 They did all the right things. Repeated measurements with different Ion chamber Electrometer Physicist Got same result that beams were all properly calibrated and delivering 1cGy/MU. Then..

29 They did all the right things. When taking down equipment, the BNC cable fell apart. Repeated measurements with new cable Results paralleled those reported by RDS. Tuned each of the beams as needed. Repeat TLD Results Energy Ratio (MDA/reported) 6 MV MV MV MeV MeV MeV MeV MeV 1.00

30 Conclusions Independent peer review of beam output is IMPORTANT because effects every patient! Only a small fraction of beam are outside of 3%. Often attributed to set-up errors, but some are actual calibration errors. Don t dismiss it, verify it. Even the best physicists can make mistakes & measurement equipment can malfunction.

31 Thank you Rebecca Howell, PhD, Director, RDS; David Followill, PhD, Director, IROC Houston QA Center; Rita Weathers (Retired 8/2016, Part-time); Debbie Tanner, Office Manager; Loretta Davis, Program Coordinator; Deborah Durdin, Research Technician II; Tera Jones, QA Dosimetrist; Ferrell Munson, Radiological Physics Technician II; Michael Sifuentes, Radiological Physics Technician I; Irene Harris, Research Dosimetrist; Jacob Palmer, Computational Scientist; David Campos, Radiological Physics Technician I; Natosha Ellis, Sr. Data Entry Operator; Ying Qiao, Computational Scientist; Susan Smith, Supervisor QA Dosimetry Services; Sharon McCallister (Retired 12/2016); Samantha Murray, Sr. Coordinator, Research Data; Kimberly Joseph, Sr. Secretary; and TaShun Thomas, Sr. Administrative Assistant. Francisco Aguirre, Medical Physicist. rds.mdanderson.org/

32 MD Anderson Dosimetry Laboratory MDADL Anthropomorphic Phantom Service (for Fee Service) End to end testing: planning and delivery Available services are: IMRT Head and Neck IMRT Prostate IMRT Spine Lung (± Motion Table) SRS Head SRS Single Beam