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Is It Feasible to Tighten the Criteria for IROC's Anthropomorphic Phantoms?

A Molineu

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


SU-E-T-543 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To analyze results of IROC Houston QA center's (RPC) H&N and prostate IMRT phantoms to determine the effect that tightening criteria would have on the phantom pass rate.

Methods: IROC Houston's anthropomorphic H&N and prostate phantoms are used to credential institution's to participate in NCI clinical trials that allow the use of IMRT. The phantoms are shipped to institutions where they are filled with water and undergo imaging, treatment planning, and irradiation as a patient would. Each phantom houses targets and organs at risk. They also hold film and TLD. Dosimeter results are compared to the institution's treatment plan using the criteria of 7% for PTV TLD doses and ≥85% pixels must pass 7%/4 mm global gamma analyses. Pass rates for the H&N and prostate phantoms were recalculated using the following tighter criteria options:
1) 5% TLD and 85% pixels 7%/4 gamma
2) 5% TLD and 90% pixels 7%/4 gamma
3) 5% TLD and 85% pixels 5%/4 gamma
Gamma analysis was repeated for the 30 most recent irradiations of each phantom to estimate results for criteria 3.

Results: Pass rates using current criteria for the H&N and prostate phantoms are 84% and 85% respectively. Pass rates since gamma criteria were introduced in 2012 are 90% and 87%. Criteria 1 applied to all irradiations drops pass rates to 78% and 82%. Applying it to only irradiations with gamma results give 77% and 84%. Applying criteria 2 to only phantoms with gamma results drops pass rates to 80% and 74% and they fall to 83% and 67% respectively using criteria 3.

Conclusion: Applying tighter criteria to phantom results has potential to increase quality in clinical trials. The results of the 30 most recent irradiations indicate that there may be room to tighten H&N phantom criteria in the future.

Funding Support, Disclosures, and Conflict of Interest: Work supported by PHS grant CA10953 and CA081647 (NCI, DHHS).

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