(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.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by IROC-Houston NCI grant #CA180803.
Keywords
Taxonomy
TH- External Beam- Photons: Quality Assurance - Linear accelerator
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