Dosimetric impact of range uncertainty in passive scattering proton therapy

Purpose The objective of this study was to investigate the dosimetric impact range uncertainty in a large cohort patients receiving passive scatter proton therapy. Methods A 120 were reviewed retrospectively, which 61 brain, 39 lung, and 20 prostate patients. Range uncertainties ±3.5% (overshooting undershooting by 3.5%, respectively) added recalculated on original plans, had been planned according our clinical planning protocol while keeping beamlines, apertures, compensators, dose grids intact. Changes coverage CTV DVH for critical organs compared analyzed. Correlation between change minimal distance also investigated. Results Although coverages maximum largely maintained most brain patients, variations over 5% still observed sporadically. Critical organs, such as brainstem chiasm, could be affected at 4 cm away from CTV. Coverage OARs lung less likely with very few exceptions. Conclusion margin recipe modern TPS leads clinically acceptable OAR doses presence uncertainties. However, pose noticeable challenge small but serial near tumors, occasionally parallel that are located distal incident beams.