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Can We Change the Acceptance Criteria for the IROC Lung Phantom Used for Credentialing Purposes?

P Alvarez*, A Molineu , P Taylor , T Nguyen , H Mehrens , N Pajot , D Followill , UT MD Anderson Cancer Center, Houston, TX


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To present the changes in the lung phantom pass rate when tighter criteria are used for the evaluation of the irradiation.

Methods: The anthropomorphic lung phantom is used to credential institutions to participate in NCI sponsored lung clinical trials. The criteria used to evaluate this test was defined based on a pilot test and approved by the study groups. The institutions planned and delivered 3D or IMRT plans that covered an ovoid shaped target located in the left lung. Motion management is included in the irradiation, if needed. All irradiations are based on plans designed with acceptable algorithms for lung dose calculations. The dose distribution criteria require ≥80% of the pixels in the ROI in each plane of evaluation to pass a 7%/5mm gamma calculation. The average of the 3 planes must be ≥85%. The new acceptance criteria proposed is a 5%/3mm for the gamma calculation.

Results: A group of 145 lung phantom irradiations were selected for this study. The algorithm for dose calculation included Collapsed Cone Convolution and Monte Carlo from different TPS, as well as AAA and Acuros from Eclipse. The pass rate was reduced from 94% to 59% due to this change in criteria. 63% of the irradiations included motion during the procedure and 68% of them used ITV technique to account for this motion. The reduction in the pass rate for static cases was less dramatic than for moving cases (from 98% to 71% for static compared to 90% to 52% with motion).

Conclusion: The tightening of the acceptability criteria reduced the number of approved irradiations by 35%. This change in evaluation parameter for a tool used in the credentialing program would impact protocol accrual.

Funding Support, Disclosures, and Conflict of Interest: This investigation was supported by IROC grant CA180803 awarded by the NCI


Lung, Phantoms


TH- External beam- photons: extracranial stereotactic/SBRT

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