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Differences in Patterns of Failure Between the Imaging and Radiation Oncology Core (IROC) Lung and Spine Phantom Irradiations

S Edward*, P Alvarez , P Taylor , A Molineu , D Followill , S Kry , UT MD Anderson Cancer Center, Houston, TX


(Wednesday, 7/17/2019) 8:30 AM - 9:30 AM

Room: Stars at Night Ballroom 2-3

Purpose: To investigate and classify the reasons why institutions fail the Imaging and Radiation Oncology Core (IROC) SBRT spine and moving lung phantoms, used to credential institutions for clinical trial participation.

Methods: All IROC moving lung and stationary SBRT spine phantom irradiation failures recorded between 2012 through 2018 were analyzed in this study. A failure was identified as an institution’s inability to meet the established IROC criteria (±7% TLDs, lung gamma: 7%/5mm, spine gamma: 5%/3 mm) for point or gamma dose agreement with TPS calculations. The reports for the failing irradiations, including point dose disagreement, dose profiles, and gamma analyses, were individually inspected and discussed with IROC physicists to determine failure mode. Classes of failure patterns were created and used to categorize each instance.

Results: We analyzed 137 (105 lung and 32 spine) phantom failures. Results were classified into 5 different category types: systematic over- and underdosing, localization errors (including specifically in the direction of motion, when applicable), local dose failures, global errors (egregious failures) and a combination category with cases displaying multiple failure modes. Fifty percent of all lung failures were due to a localization error in the direction of motion (superior-inferior motion), while only 13% of failures were localization errors in other directions. Systematic dose errors contributed to 22% of the lung failures. In contrast, the majority (56%) of spine phantom failures were due to systematic dose errors, with localization errors only accounting for 13% of failures.

Conclusion: There were two distinct patterns of failure between the IROC moving lung and SBRT spine phantoms: majority of lung phantom failures were due to localization errors in the direction of motion, whereas the spine phantom failures were largely attributable to systematic dose errors. Both of these errors are clinically relevant and could manifest as errors in patient treatments.


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