Program Information
Collimation Methods in Spot Scanning Proton Therapy: A Treatment Plan Comparison Between a Fixed Aperture and a Dynamic Collimation System
B Smith1*, E Gelover1 , D Wang1 , A Moignier1 , R Flynn1 , L Lin2 , M Kirk2 , T Solberg2 , D Hyer1 , (1) University of Iowa Hospitals and Clinics, Iowa City, IA, (2) University of Pennsylvania, Philadelphia, PA
Presentations
SU-E-T-187 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Low-energy treatments during spot scanning proton therapy (SSPT) suffer from poor conformity due to increased spot size. Collimation devices can reduce the lateral penumbra of a proton therapy dose distribution and improve the overall plan quality. The purpose of this work was to study the advantages of individual energy-layer collimation, which is unique to a recently proposed Dynamic Collimation System (DCS), in comparison to a standard, fixed aperture that allows only a single shape for all energy layers.
Methods: Three brain patients previously planned and treated with SSPT were re-planned using an in-house treatment planning system capable of modeling collimated and un-collimated proton beamlets. The un-collimated plans, which served as a baseline for comparison, reproduced the target coverage of the clinically delivered plans. The collimator opening for the aperture based plans included a 0.6 cm expansion of the largest cross section of the target in the Beam’s Eye View, while the DCS based plans were created by optimizing the collimator position for beam spots near the periphery of the target in each energy layer.
Results: The reduction of mean dose to normal tissue adjacent to the target, as defined by a 10 mm ring, averaged 9.13% and 3.48% for the DCS and aperture plans, respectively. The conformity index, as defined by the ratio of the volume of the 50% isodose line to the target volume, yielded an average improvement of 16.42% and 8.16% for the DCS and aperture plans, respectively.
Conclusion: Collimation reduces the dose to normal tissue adjacent to the target and increases dose conformity to the target region for low-energy SSPT. The ability of the DCS to provide collimation to each energy layer yields better conformity in comparison to fixed aperture plans.
Funding Support, Disclosures, and Conflict of Interest: This work was partially funded by IBA (Ion Beam Applications S.A.).
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