srs/sbrt errors and causes · 2014-06-25 · srs/sbrt errors and causes ryan foster, ph.d....
TRANSCRIPT
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SRS/SBRT Errors and Causes
Ryan Foster, Ph.D.Assistant Professor
Director of Clinical Medical PhysicsDepartment of Radiation OncologyUT Southwestern Medical Center
Dallas, TX
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Disclosures
• I receive research funding from the Cancer Prevention and Research Institute of Texas.
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Outline of Presentation
• Introduction• Summary of accidents and misadministrations• Resources and guidance• Conclusions
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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!
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What are the sources of errors?
WHORadiotherapy Risk Profile 2008
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According to the WHO Radiotherapy Risk Profile, what are the two most common sources of actual adverse events in radiation therapy?
4%4%87%2%3% 1. Positioning/immobilization and commissioning
2. Simulation/imaging and treatment planning3. Commissioning and treatment planning4. Planning and treatment information transfer5. Commissioning and treatment information
transfer
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Answer
WHORadiotherapy Risk Profile 2008
3. Commissioning and treatment planning
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Two Major Categories in SRS/SBRT Accidents
• Commissioning – Small field measurements– Absolute calibration
• Treatment parameter transfer– SRS Cones– Wrong side/site treatments
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SUMMARY OF INCIDENTS
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Small field commissioning
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Small field commissioning
This happened in France in 2007 and was reported in 2008!
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Small field commissioning
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No communication
How many patients in Missouri could have received the correct treatment if the incident in France had been more widely reported?
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Small field measurement issues persist
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According to TG101, an appropriate measurement device for SRS/SBRT small
fields would be a
62%31%6%1%0% 1. 0.6 cc Farmer chamber
2. CC13 ion chamber3. Parallel plate chamber4. 0.015 cc pinpoint ion chamber5. Stereotactic diode
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Answer
5. Stereotactic diode
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Wellhofer
ExradinPTW
PTW
IBA SFDPTW
Sun Nuclear
Much more detail coming in tomorrow’s presentations!
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Small Field Output Factors
Das, Ding and Ahnesjo. Med Phys Vol. 35, No.1, 2008.
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A 1x1 cm2 6 MV output factor measured with a 0.6cc Farmer chamber
1%6%1%0%92%1. Would be 40% smaller than the true output factor
2. Would be the true output factor3. Would be 5% smaller than the true factor4. Would be 50% larger than the true factor5. Would be 10% larger than the true factor
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Answer1. Would be 40% smaller than the true output
factor.
Das, Ding and Ahnesjo. Med Phys Vol. 35, No.1, 2008.
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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
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Miscalibration of SRS Linac
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Independent Check of Calibration
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Improper Jaw Size During SRS
In 2004, physicist told therapist to set a “40x40” for cone SRS treatment; therapist set 40x40 cm2
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
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Improper Jaw Size During SRS
This occurred in France in 2004!
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SRS Cone Left Out
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State of Texas Response
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Checklists!
• Appendix of Solberg et al. PRO 2011 provides excellent examples of checklists for SRS, SBRT, simulation and treatment planning
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GammaKnife Misadministrations
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GammaKnife Misadministrations
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Analysis of GammaKnife Errors
Goetsch IJROBP Vol. 71, No. 1, Supplement, S118-S121, 2008.
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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!
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Dosimetric commissioning: Do your calculations agree with measurement?
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Dosimetric commissioning: Do your calculation agree with measurement?
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Patient Specific QA
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What About Localization Accuracy?
Must perform end to end tests!
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RPC Lung Phantom
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RPC Spine Phantom
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RPC H&N Phantom
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Planning
R/V
Tx Unit
Are your electronic systems configured correctly?
Do all of your commissioning in clinical mode and through your R/V system
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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
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SRS/SBRT White Paper• Solberg et al. Quality and safety considerations
in stereotactic radiosurgery and stereotactic body radiation therapy. PRO 2012.
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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!
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International Resources
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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
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Summary | Conclusion• SRS and SBRT are ABLATIVE treatments!• Care must be taken during commissioning• Plan your program carefully!
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Thank you!