Program Information
Plan Deliverability Is Not Compromised by Complexity for VMAT Treatments
L Apicello1*, J James1 , E Martin1 , B Nelms2 , B Wang1 , (1) University of Louisville, Louisville, KY, (2) Canis Lupis LLC, Merrimac, Wisconsin
Presentations
SU-K-FS1-14 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: Four Seasons 1
Purpose: Several retrospective studies have evaluated the correlation between complexity metrics and the deliverability of Intensity Modulated Radiation Therapy (IMRT). The purpose of this study is to further investigate this correlation with a prospective study that eliminates the patient variation of tumor size and location by using a single CT and structure set for a specific site.
Methods: Five Volume Modulated Arc Treatment (VMAT) plans over a range of modulation complexity were created for each of five patient datasets from AAPM MPPG 5.a: Commissioning and QA of Treatment Planning Dose Calculations for prostate, abdomen, lung, anus, and head and neck. The plans were created on a Varian Eclipse planning station (version 11). The levels of complexity are specified by a plan score calculated from Dose Volume Histogram (DVH) metrics. The metrics were determined by the consensus of a group of radiation oncologist. Every plan was measured on a Varian TrueBeam using a ScandiDos Delta⁴ phantom. The criteria of the gamma analysis was 2%/2mm with a threshold of 10%.
Results: The plan scores varied from 65 to 143 on a scale of 0 to 150. The minimum gamma passing rate was 83.8% for all 25 plans, with four of the five sites all above 90%. Contrary to common theory, the gamma passing rate increases as the plan score/complexity increases for all treatment sites. The R values range from 0.628 to 0.976. An even stronger correlation is found between the gamma results and the number of MU, with four R values over 0.90.
Conclusion: This study reveals that the relationship between complexity and deliverability is not as previously understood for VMAT plans created in the Eclipse planning station and delivered on a Varian TrueBeam. The complexity of a plan should not be compromised due to uncertainty that the plan will be deliverable.
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