Effects of Breathing on Dose Distribution in Heavy-Ion Radiotherapy Based on Medical Image Processing

Heavy ion dose distribution is sensitive to anatomic changes and tissue motion due to high dose concentrated on Bragg peak with high relative biological effectiveness (RBE). During treating target sites especially in lung cancer cases, breathing motion may result unintended variations in the dose distribution. Based on image registration, segmentation and pseudo-color algorithm, the work conducts a study on the calculation and visualization of the heavy dose distribution for 3D superimposed conformal irradiation and dose evaluation. Then the paper investigates the respiratory motion effects on the dosimetric redistribution on target and critical tissues during heavy ion radiotherapy. In our experiments, ten patients have been undergone routine free breathing CT scan, two additional CT scans at the end of inspiration and the end of expiration. The results have showed that clinical target volume (CTV) coverage is compromised markedly due to respiration. The paper suggests a real-time respiratory gating system and adjustable dramatic multi-leaf collimator should be adopted in lung cancer cases for heavy ion radiotherapy with small CTV-to-PTV margin