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Retrospective Dosimetric Analysis of Brain Lesions Treated with Conformal Arc Stereotactic Radiosurgery

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J Leasure

J Leasure*, V Ulizio , D Pearson , University of Toledo, Toledo, OH


SU-I-GPD-T-568 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The purpose of this study is to compare the plan quality of an institution’s conformal arc radiotherapy treatments for brain lesions to average values reported worldwide. This retrospective study will utilized the RTOG and Paddick Conformity Indices and several other common indices for comparison.

Methods: Treatment plans were assessed using the institutions primary planning system. For patients (N = 41) presenting with brain lesions (n = 82) small enough to be treated with conformal arc radiotherapy via the SRS dedicated linear accelerator, the RTOG conformity index, Paddick conformity index, conformity gradient index, gradient index, and dose gradient index were determined for each plan. These indices were then compared to values found from other institutional studies and to the values considered acceptable in the definition of the indices. The lesions were then separated into categories based on size. The indices were determined for each size group (small <2cc, medium 2-10cc, and large >10cc) and a correlation between size and index value was found.

Results: Average values for each of the following indices were calculated for all sizes of lesions: RTOG conformity index = 1.36 ± 0.29; Paddick conformity index = 0.72 ± 0.12; conformity gradient index = 214.67 ± 12.35; gradient index = 3.64 ± 1.09; dose gradient index = -0.11 ± 0.16. Results for each size group are shown in the supporting document.

Conclusion: Based on the values reported, this institution provides favorable conformity of dose to intracranial target lesions. The Paddick Conformity Index, although being acceptable, was lower than expected. This was determined to be a result of many of the lesions being in the small category. Because of the size of these lesions, small variations in dose volume produce proportionally larger errors on the indices.

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