SU‐E‐T‐439: Fundamental Verification of Respiratory‐Gated Spot Scanning Proton Beam Therapy

Abstract

Purpose:The spot‐scanning proton beam irradiation with respiratory gating technique provides quite well dose distribution and requires both dosimetric and geometric verification prior to clinical implementation. The purpose of this study is to evaluate the impact of gating irradiation as a fundamental verification.Methods:We evaluated field width, flatness, symmetry, and penumbra in the gated and non‐gated proton beams. The respiration motion was distinguished into 3 patterns: 10, 20, and 30 mm. We compared these contents between the gated and non‐gated beams. A 200 MeV proton beam from PROBEAT‐III unit (Hitachi Co.Ltd) was used in this study. Respiratory gating irradiation was performed by Quasar phantom (MODUS medical devices) with a combination of dedicated respiratory gating system (ANZAI Medical Corporation). For radiochromic film dosimetry, the calibration curve was created with Gafchromic EBT3 film (Ashland) on FilmQA Pro 2014 (Ashland) as film analysis software.Results:The film was calibrated at the middle of spread out Bragg peak in passive proton beam. The field width, flatness and penumbra in non‐gated proton irradiation with respiratory motion were larger than those of reference beam without respiratory motion: the maximum errors of the field width, flatness and penumbra in respiratory motion of 30 mm were 1.75% and 40.3% and 39.7%, respectively. The errors of flatness and penumbra in gating beam (motion: 30 mm, gating rate: 25%) were 0.0% and 2.91%, respectively. The results of symmetry in all proton beams with gating technique were within 0.6%.Conclusion:The field width, flatness, symmetry and penumbra were improved with the gating technique in proton beam. The spot scanning proton beam with gating technique is feasible for the motioned target.