Author: Austen N. Curcuru, Winter Green, Yao Hao, Jiayi Liu, Yuting Peng, Tiezhi Zhang, Xiandong Zhao 👨🔬
Affiliation: Washington University School of Medicine, Department of Radiation Oncology, WashU Medicine, Virginia Commonwealth University, Washington University School of Medicine, Washington University in St. Louis 🌍
Purpose: We proposed a treatment planning optimization method that utilizes customized spot map modification to achieve less dosimetry uncertainty, monitor unit ratio (MUR) and neutron dose in a spot scanning proton system with adaptive aperture (AA), which is a multileaf collimator (MLC) system. The objective of this study is to investigate the feasibility of achieving higher gamma passing rate on MatriXX QA and faster treatment delivery by eliminating the spots too close to MLC during treatment.
Methods: An in-house script was developed to produce customized spots map for a spot scanning proton system before the treatment planning system starts the spots weight optimization. To evaluate the necessities of eliminating spots at different scenarios, Lynx and film measurements were performed. Monte-Carlo (MC) simulation was performed in Geant4 and TOPAS as the secondary check for the measurement and as a tool to further investigate the neutron dose reduction.
Results: Based on the MC simulation, and Lynx/film measurements, the dosimetry uncertainty is mainly from the high weight spots closed to curved edge of dynamic block. The new optimized plan with spot map modification shows similar target coverage and OAR sparing. The QA measurements were in better agreement with the TPS dose calculation, with a higher gamma passing rate of >=99.5% using a standard 3%/3mm criteria. The spot map modified plans with 3 and 5 mm minimal distance to dynamic block’s curved edge, shows 8% and 15% reduction from several thousands total MU, respectively. Neutron dose shows significant reduction as well, in our in-house MC simulation.
Conclusion: Our work demonstrated the feasibility of a spot map modified plan to reduce the treatment delivery time, total MU number and less neutron dose production. The implementation of this method also avoids the potentials of dosimetry uncertainty on a spot scanning proton system with adaptive aperture.