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A Treatment Planning Comparison of Photon and Proton Radiotherapy for Intra-Cranial Stereotactic Radiosurgery Lesions

A Boczkowski

A Boczkowski1*, F Bova2 , T Willoughby3 , J Pukala4 , S Meeks5 , (1) University of Florida, Gainesville, FL, (2) Univ Florida, Gainesville, FL, (3) UF Health Cancer Center at Orlando Health, Orlando, FL, (4) UF Health Cancer Center at Orlando Health, Orlando, FL, (5) UF Health Cancer Center at Orlando Health, Orlando, FL


SU-I-GPD-T-155 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To quantify the differences in photon and proton intra-cranial stereotactic radiosurgery (SRS) treatment plans, to determine the optimal number of beams, and to determine the optimal beam arrangement to deliver comparable proton plans.

Methods: Differences in volumetric modulated arc therapy and conventional cone planning for photon SRS patients of various tumor sizes, tumor complexities and tumor types was previously studied. The photon treatment plans, including CT and MR image sets, structures set, dose volume histogram, and dose for each subject, were exported from a commercial treatment planning system (TPS). Patient data will be transferred to a proton commercial TPS and will be re-planned using proton beam delivery techniques and methods. Re-planning of each patient will go through multiple iterations include varying number of beams (ranging from 1 - 20+ beams) and optimization of beam arrangement. The proton iterations will be compared based on dose volume histogram data. The photon and proton plans are to be evaluated on excess prescription volume, prescription isodose volume to target volume ratio, dose gradient, conformity/gradient index.

Results: Initial proton re-plans show an increase number of beams and an arc-based arrangement increase the conformity of the tumor volume. Re-plans including 1, 5, 10, 15, 18, and 21 beams showed 90% of the dose (V90%) is delivered to 20%, 78%, 89%, 90%, 95%, and 97% of the tumor volume, respectively.

Conclusion: Initial results from this study indicate that an increase in the number of proton beams in an arc-based arrangement allows for increased dose conformity to the tumor volume as evidence by the increase in the V90% with increasing beam number. These results are expected to be seen throughout the remaining patient cohort. Furthermore, the results will allow a comprehensive photon-proton planning comparison to be conducted.

Funding Support, Disclosures, and Conflict of Interest: Funded by the Florida High Tech Corridor Council

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