SRS/SBRT Errors and Causes Ryan Foster, Ph.D. Assistant Professor Director of Clinical Medical Physics Department of Radiation Oncology UT Southwestern Medical Center Dallas, TX
Disclosures I receive research funding from the Cancer Prevention and Research Institute of Texas.
Outline of Presentation Introduction Summary of accidents and misadministrations Resources and guidance Conclusions
Learning Objectives To learn from previous accidents and misadministrations during SRS/SBRT To understand the types of errors that can occur To understand how to prevent these errors from happening to you!
What are the sources of errors? WHO Radiotherapy Risk Profile 2008
According to the WHO Radiotherapy Risk Profile, what are the two most common sources of actual adverse events in radiation therapy? 3% 1. Positioning/immobilization and commissioning 2% 87% 4% 4% 2. Simulation/imaging and treatment planning 3. Commissioning and treatment planning 4. Planning and treatment information transfer 5. Commissioning and treatment information transfer
Answer 3. Commissioning and treatment planning WHO Radiotherapy Risk Profile 2008
Two Major Categories in SRS/SBRT Accidents Commissioning Small field measurements Absolute calibration Treatment parameter transfer SRS Cones Wrong side/site treatments
SUMMARY OF INCIDENTS
Small field commissioning
Small field commissioning This happened in France in 2007 and was reported in 2008!
Small field commissioning
No communication How many patients in Missouri could have received the correct treatment if the incident in France had been more widely reported?
Small field measurement issues persist
According to TG101, an appropriate measurement device for SRS/SBRT small fields would be a 0% 1. 0.6 cc Farmer chamber 1% 6% 31% 62% 2. CC13 ion chamber 3. Parallel plate chamber 4. 0.015 cc pinpoint ion chamber 5. Stereotactic diode
5. Stereotactic diode Answer
PTW Exradin PTW Wellhofer Much more detail coming in tomorrow s presentations! PTW IBA SFD Sun Nuclear
Small Field Output Factors Das, Ding and Ahnesjo. Med Phys Vol. 35, No.1, 2008.
A 1x1 cm 2 6 MV output factor measured with a 0.6cc Farmer chamber 92%1. Would be 40% smaller than the true output factor 0% 2. Would be the true output factor 1% 3. Would be 5% smaller than the true factor 6% 4. Would be 50% larger than the true factor 1% 5. Would be 10% larger than the true factor
Answer 1. Would be 40% smaller than the true output factor. Das, Ding and Ahnesjo. Med Phys Vol. 35, No.1, 2008.
How do you know if your data is good? Compare with Other Institutions / Machines Followill et al. JACMP 2012 and Erratum, JACMP Vol 15, No 2, 2014
Miscalibration of SRS Linac
Independent Check of Calibration
Improper Jaw Size During SRS In 2004, physicist told therapist to set a 40x40 for cone SRS treatment; therapist set 40x40 cm 2 Some normal tissue received more dose than the target; developed fibrosis and oeso-tracheal fistula requiring surgery; patient died from brutal haemorrhage a few days after surgery LESSONS FROM RECENT ACCIDENTS IN RADIATION THERAPY IN FRANCE, S. Derreumaux*, C. Etard, C. Huet, et al. Institut de Radioprotection et de Suˆ rete Nucle aire, Direction de la Radioprotection de l Homme, IRSN, BP 17, F-92262 Fontenay-aux-Roses Cedex, France Radiation Protection Dosimetry (2008), Vol. 131, No. 1, pp. 130 135
Improper Jaw Size During SRS This occurred in France in 2004!
SRS Cone Left Out
State of Texas Response
Checklists! Appendix of Solberg et al. PRO 2011 provides excellent examples of checklists for SRS, SBRT, simulation and treatment planning
GammaKnife Misadministrations
GammaKnife Misadministrations
Analysis of GammaKnife Errors Goetsch IJROBP Vol. 71, No. 1, Supplement, S118-S121, 2008.
Beam data acquisition for SRS / SBRT is challenging and time consuming Small fields Sharp gradients Detector position-orientation effects Loss of lateral electron equilibrium Must get this right! Commissioning errors affect all patients treated with the device not just a select few!
Dosimetric commissioning: Do your calculations agree with measurement?
Dosimetric commissioning: Do your calculation agree with measurement?
Patient Specific QA
Must perform end to end tests! What About Localization Accuracy?
RPC Lung Phantom
RPC Spine Phantom
RPC H&N Phantom
Planning R/V Are your electronic systems configured correctly? Do all of your commissioning in clinical mode and through your R/V system Tx Unit
AAPM/ASTRO Resources AAPM Task Group 101 Target Safely IMRT Safety White Paper Target Safely SBRT/SRS Safety White Paper ASTRO Safety is no accident A framework for quality radiation oncology and care
SRS/SBRT White Paper Solberg et al. Quality and safety considerations in stereotactic radiosurgery and stereotactic body radiation therapy. PRO 2012.
SRS/SBRT White Paper Key Points Focus on personnel qualifications and technology requirements Commissioning/credentialing/QA SRS and SBRT are SPECIALIZED procedures and should be treated as such!
International Resources
Specific Lessons Learned from Accidents and Overexposures Get an independent check of machine calibration and commissioning Perform end to end commissioning tests, including the R&V system Use an independent method to check MU/time calculations Evaluate changes in TPS, R&V and other software thoroughly before implementation Carefully plan your program
Summary Conclusion SRS and SBRT are ABLATIVE treatments! Care must be taken during commissioning Plan your program carefully!
Thank you!