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A Point/Counterpoint On Current and Future Directions for Patient Specific QA

X Tang1*, S Kry2*, A McNiven3*, (1) Yale New Haven Hospital, New Haven, CT, (2) The University of Texas MD Anderson Cancer Center, Houston, TX, (3) Princess Margaret Cancer Centre, Toronto, ON, CA


(Monday, 7/13/2020) 1:00 PM - 2:00 PM [Eastern Time (GMT-4)]

Room: Track 3

Patient specific Intensity Modulated Radiation Therapy (IMRT) Quality Assurance (QA) is important to the success of IMRT treatment. Today, the device based IMRT QA is widely used as a routine technique. Moving forward, as Linac and MLC become more reliable, IMRT QA might shift towards a different procedure. In this section, we review the pros and cons of QA methods/devices, asking the question what would be a better way to do IMRT QA in the future. Specifically, speaker 2 will present point—current patient specific QA will remain an essential part of our practice. Speaker 3 will present counterpoint that calculation based QA should be the future.

Patient Specific QA Measurements Will Remain an Essential Part of Medical Physics Practice
1. Key role in commissioning new devices and techniques
a. Achievable results available in the literature
b. Clear recommendations, well-established techniques
2. Can provide a standard baseline for performance and end-to-end delivery across changes in infrastructure or use of infrastructure that other measurement techniques may not be able to, track trends, changes, as a whole or specific sites.
3. Important in multi-centre comparisons (use provincial IMRT QA program as an example, can identify/highlight techniques where machine performance may play a bigger role - example where decrease in specific clinical site related to MLC performance, examples where variation in planning practice (e.g. complexity) impacted delivery results)

Limitations with current IMRT QA and proposal of the future calculation based IMRT QA
1. Current methods for IMRT QA don’t work (they have very poor sensitivity)
a. Compared to IROC phantom results
• People’s IMRT QA results look great even when the phantom result is a train wreck. This has been evaluated in a couple of publications and we have some nice new data to further reinforce this
b. When evaluating clinical plans
• Evaluations of clinical plans show similar poor performance from IMRT QA techniques
2. Criteria used in IMRT QA is too loose (excessive specificity)
a. From clinical plan evaluations and from IROC evaluations, devices need ~100% of pixels passing used as the threshold in order to catch anything.
3. Calculation-based approach was not perfect, but outperformed measurement based techniques
a. We completed this study recently, again looking at IROC phantom failures.

Learning Objectives:
1. Pros and cons of current measurement based IMRT QA
2. Pros and cons of calculation based IMRT QA



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