Treatment Planning of Total Marrow Irradiation with Intensity-Modulated Spot-Scanning Proton Therapy
D Zuro1*, G Vidal1, C Henson1, Y Chen1, C Han2, S Hui3, S Ahmad1, I Ali1, (1) University of Oklahoma Health Sciences Center, Edmond, OK, (2) City of Hope Medical Center, Duarte, CA, (3) Beckman Research Institute, Duarte, CA
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PO-GePV-T-172 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: The goal of this study is to investigate treatment planning of total marrow irradiation (TMI) using intensity-modulated spot-scanning proton therapy (IMPT). The dosimetric parameters of the intensity modulated proton plans were evaluated and compared with the corresponding TMI-plans generated with volumetric-modulated-arc-therapy (VMAT) using photon beams.
Methods: Intensity-modulated proton plans for TMI were created using the Monte-Carlo dose-calculation algorithm in Raystation-11A with spot-scanning-proton-beams from the MEVION S250i Hyperscan system. Patients were treated with four isocenters placed along the longitudinal direction each with a set of 5 beams for a total of 20 beams. VMAT TMI-plans were generated with the Eclipse-V16 analytical anisotropic algorithm for a Varian Trilogy machine. Three planning-target-volumes (PTV) bones, ribs, and spleen were covered by 12Gy. The dose conformality-index, D80, D50 and D10 for PTVs and OARs for the IMPT-plans were quantified and compared with the corresponding VMAT-plans.
Results: The dose for most of the OARs was reduced substantially (5% and more) in the IMPT-plans for TMI in comparison with VMAT-plans with photons, while maintaining comparable dose coverage for the PTV’s. This dose reduction is due to the fast dose fall-off of the distal Bragg-peak in the proton plans. The conformality-index was found to be similar (0.8) for the photon and proton plans. IMPT-plans provided superior superficial dose coverage for the skull and ribs in comparison with VMAT because of increased dose deposition by the proton beams.
Conclusion: Treatment plans for TMI generated with IMPT were superior to VMAT-plans mainly due to large reduction in organs at risk dose. Although the technology for IMPT-TMI is not available now, this is a feasibility study that represent a proof-of-concept providing an enticing alternative to conventional TMI with photon with superior dose coverage of the targets, sparing of OAR and radiobiological effects associated with proton therapy.
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