Objective. Evaluation of Linear Accelerator Performance Standards using an Outcome Oriented Approach. Linac performance standards*

Transcription

1 Quality in Radiation Therapy: what is it and how do you achieve it?. Overview of definitions and approaches to Quality Pawlicki. ROSIS Knöö öös. Peer Review Quality Audits Halvorsen. The Regulator s s Viewpoint Zelac. QA in IGRT Bissonnette 6. Evidence Based QA Dunscombe Evaluation of Linear Accelerator Performance Standards using an Outcome Oriented Approach Alejandra Rangel, Nicolas Ploquin, Ian Kay, Peter Dunscombe Medical Physics, (8) - 8 Objective To quantify the dosimetric changes resulting from sub-optimal machine performance 6. Evidence Based Quality assurance Linac performance standards* Performance standards are stated in terms of tolerance & action levels levels are considered not to compromise treatment quality levels require an intervention * P. Dunscombe, C. Arsenault, JP. Bissonnette, et. al. "The development of quality control standards for radiation therapy equipment in Canada," J. Appl. Clin. Med. Phys 8, 8-8 (7)

2 Linac performance characteristics 8 DCRT plans constancy angle readouts angle readouts Laser alignment (x) indicator 7 -field conformal plans ( MV beams) 7 - field conformal plans 7 -field tangential plans 7-8 field conformal plans Evaluation of Levels of Performance CAPCA standards Test constancy % % Simulation of a Linac performance deviation Positive deviation Negative deviation Positive deviation Negative deviation X 7 plans X 8 Linac performance characteristics X ~ 9 Simulations levels X directions

3 Calculation of EUD Results: Brain CTV 8 reference plans + ~9 test plans Change in EUD (%)... Brain Treatment CTV & CTV. Equivalent Uniform Dose CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV CTV Bars = Average EUDEUD per course of treatment Error bars = Std dev for n = 7 Results: Brain OARs Results: Prostate CTV Change in EUD (Gy) 6 Brain Treatment Brainstem & Optic Chiasm Change in EUD (%)... Prostate Treatment CTV. Brainst.Opt.chiasm B O B O B O B O B O B O B O st bar in each section = Brain Stem effects nd bar in each section = Optic Chiasm effects Bars = Average EUDEUD per course of treatment Error bars = Std dev for n = 7

4 Results: Prostate OARs Sensitivity analysis Change in EUD (Gy) 6 Prostate Treatment Bladder & Rectum Bladder Rectum B R B R B R B R B R B R B R st bar in each section = Bladder effects nd bar in each section = Rectum effects The a value used in the calculation of the Equivalent Uniform Dose is not known accurately For a ±% change in a our results vary by <. Gy for the organs at risk <.% for the targets 6. Evidence Based quality Assurance Conclusions CAPCA Levels are shown to maintain average EUD deviations to within % and Gy. However they show markedly different effects over the range of % or Gy. The efficiency with which resources are allocated within a linac quality control program can be enhanced by analyzing the relative importance of the various performance standards. Final Thoughts Will these results provoke a re-write of TG? NO Will these results guide the distribution of QC resources? MAYBE Will there be more work on putting QA programs on an objective basis? HOPEFULLY

5 .radiation oncology researchers need to further develop methodology for critical assessment of health technologies as a complement to randomized controlled trials. Søren Bentzen. Randomized controlled trials in health technology assessment: Overkill or overdue? Radiotherapy and Oncology 86 (8) -7 7 Quality in Radiation Therapy: What it is and how do you achieve it? Wednesday th July; am Noon Room AAPM Annual Meeting July, 8