A 4D-optimization concept for scanned ion beam therapy

Abstract

Background and purposeScanned carbon beam therapy offers advantageous dose distributions and an increased biological effect. Treating moving targets is complex due to sensitivity to range changes and interplay. We propose a 4D treatment planning concept that considers motion during particle number optimization. Material and methodsThe target was subdivided into sectors, one for each motion phase of a 4D-CT. Each sector was non-rigidly transformed to its motion phase and there targeted by a dedicated raster field (RST). Therefore, the resulting 4D-RST compensated target motion and range changes. A 4D treatment control system (TCS) was needed for synchronized delivery to the measured patient motion. 4D-optimized plans were simulated for 9 NSCLC lung cancer patients and compared to static irradiation at end-exhale. A prototype TCS was implemented and successfully tested in a film experiment. ResultsThe 4D-optimized treatment plan resulted in only slightly lower dose coverage of the target compared to static optimization, with V95% of 97.9% (median, range 96.5–99.4%) vs. 99.3% (98.5–99.8%), with negligible overdose. The conformity number was comparable at 88.2% (85.1–92.5%) vs. 85.2% (79.9–91.2%) for 4D and static, respectively. ConclusionWe implemented and tested a 4D treatment plan optimization method resulting in highly conformal dose delivery.