Dosimetric impact of range uncertainty in passive scattering proton therapy

• Published in: Journal of applied clinical medical physics Vol. 22; no. 5; pp. 6 - 14
• Main Authors: Liu, Ruirui, Sun, Baozhou, Zhang, Tiezhi, Williamson, Jeffery F., O’Sullivan, Joseph A., Zhao, Tianyu
• Format: Journal Article
• Language: English
• Published: United States John Wiley & Sons, Inc 01.05.2021; John Wiley and Sons Inc
• Subjects: Brain cancer; Calibration; Cancer therapies; dose calculation; Dosimetry; Lung cancer; passive scatter proton therapy; Patients; Planning; Prostate cancer; proton range uncertainty; Radiation Oncology Physics; Radiation therapy; retrospective study; dose calculation; proton range uncertainty; passive scatter proton therapy; retrospective study
• ISSN: 1526-9914; 1526-9914
• DOI: 10.1002/acm2.13179

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