SRS/SBRT Errors and Causes

Transcription

1 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

2 Disclosures I receive research funding from the Cancer Prevention and Research Institute of Texas.

3 Outline of Presentation Introduction Summary of accidents and misadministrations Resources and guidance Conclusions

4 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!

5 What are the sources of errors? WHO Radiotherapy Risk Profile 2008

6 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

7 Answer 3. Commissioning and treatment planning WHO Radiotherapy Risk Profile 2008

8 Two Major Categories in SRS/SBRT Accidents Commissioning Small field measurements Absolute calibration Treatment parameter transfer SRS Cones Wrong side/site treatments

9 SUMMARY OF INCIDENTS

10 Small field commissioning

11 Small field commissioning This happened in France in 2007 and was reported in 2008!

12 Small field commissioning

13 No communication How many patients in Missouri could have received the correct treatment if the incident in France had been more widely reported?

14 Small field measurement issues persist

15

16 According to TG101, an appropriate measurement device for SRS/SBRT small fields would be a 0% cc Farmer chamber 1% 6% 31% 62% 2. CC13 ion chamber 3. Parallel plate chamber cc pinpoint ion chamber 5. Stereotactic diode

17 5. Stereotactic diode Answer

18 PTW Exradin PTW Wellhofer Much more detail coming in tomorrow s presentations! PTW IBA SFD Sun Nuclear

19 Small Field Output Factors Das, Ding and Ahnesjo. Med Phys Vol. 35, No.1, 2008.

20 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

21 Answer 1. Would be 40% smaller than the true output factor. Das, Ding and Ahnesjo. Med Phys Vol. 35, No.1, 2008.

22 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

23 Miscalibration of SRS Linac

24 Independent Check of Calibration

25 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 Fontenay-aux-Roses Cedex, France Radiation Protection Dosimetry (2008), Vol. 131, No. 1, pp

26 Improper Jaw Size During SRS This occurred in France in 2004!

27 SRS Cone Left Out

28 State of Texas Response

29 Checklists! Appendix of Solberg et al. PRO 2011 provides excellent examples of checklists for SRS, SBRT, simulation and treatment planning

30 GammaKnife Misadministrations

31 GammaKnife Misadministrations

32 Analysis of GammaKnife Errors Goetsch IJROBP Vol. 71, No. 1, Supplement, S118-S121, 2008.

33 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!

34 Dosimetric commissioning: Do your calculations agree with measurement?

35 Dosimetric commissioning: Do your calculation agree with measurement?

36 Patient Specific QA

37 Must perform end to end tests! What About Localization Accuracy?

38 RPC Lung Phantom

39 RPC Spine Phantom

40 RPC H&N Phantom

41 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

42 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

43 SRS/SBRT White Paper Solberg et al. Quality and safety considerations in stereotactic radiosurgery and stereotactic body radiation therapy. PRO 2012.

44 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!

45 International Resources

46 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

47 Summary Conclusion SRS and SBRT are ABLATIVE treatments! Care must be taken during commissioning Plan your program carefully!

48 Thank you!