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Comparison of Clinical Trial and Non-Trial Pass Rates for IROC Houston's HN and Lung Phantoms

H Mehrens*, T Nguyen, N Hernandez, B Lewis, N Pajot, A Molineu, D Followill, The University of Texas MD Anderson Cancer Center, Houston, TX


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To evaluate and compare passing rates for IROC Houston’s HN and lung phantoms irradiated for NCI clinical trials, non-NCI clinical trials and non-trial purposes during the past 5 years.

Methods: The HN phantom contains a primary and secondary PTV and the lung phantom contains a pill-shaped PTV embedded in lung equivalent material. Both phantoms hold TLD and radiochromic film and are mailed to institutions for NCI trial credentialing, non-NCI trial credentialing and non-trial end-to-end QA purposes. Passing criteria for the HN and lung phantoms are: TLD/TPS ±7% and = 85% of pixels passing a 7%/4mm gamma analysis and TLD/TPS within 0.92 – 1.05 and = 80% of pixels passing a 7%/5mm gamma analysis with the average over three planes = 85% of pixels passing, respectively. Pass rates of phantoms irradiated from 2015 to present were calculated and compared using the Pearson chi-squared test.

Results: The average HN phantom pass rate was 94% with: 94% for NCI clinical trials (N = 412), 95% for non-NCI clinical trials (N = 131) and 93% for non-trial (N = 402) irradiations. None were statistically significantly different. The lung phantom pass rate was 86% with: 84% for NCI clinical trials (N = 450), 83% for non-NCI clinical trials (N = 142) and 89% for non-trial (N =513) irradiations. The non-trial lung phantom pass rate was significantly different from each of the other two.

Conclusion: The differences in the lung phantom pass rates may be due to increased difficulty of the lung phantom. Perhaps the non-trial sites irradiated the phantom at the time of system commissioning and were paying closer attention to detail during irradiation than the other irradiations.

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Funding Support, Disclosures, and Conflict of Interest: This work was supported by IROC-Houston NCI grant #CA180803.


Quality Assurance, Phantoms


TH- External Beam- Photons: Quality Assurance - Linear accelerator

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