The Accuracy Heart Dosimetric Study of Left-breast Cancer Radio-therapy using Deformable Image Registration

The radiation injury of heart is an obviously risk in left-breast cancer radiotherapy. In this study, the uncertainty of intra-fraction and inter-fraction for heart dose was investigated using the 4DCT, CBCT and deformable image registration (DIR) to understand the exact dose. The secondary objective of this study was to evaluate the impact of DIR uncertainty on dose accumulation. 4DCT and CBCT images were scanned for ten left-breast cancer patients before and during 3D-CRT treatment. An anatomically constrained hybrid DIR method and a biomechanical model based DIR method were applied to dose accumulation. Dose scenarios included plan dose (no motion), 4D dose (intra-fraction motion) and accumulated dose (inter-fraction motion). The doses to the heart were assessed. the differences among plan heart dose, 4D heart dose and accumulated dose of the investigated parameters D-mean, D-max, V-10, V-20, V-30 and V-40 were ranged -3.8 similar to 7.1%, -0.6 similar to 0.5%, -1.3 similar to 0.8%, -0.8 similar to 1.7%, -0.8 similar to 1.7% and -0.5 similar to 2.2% respectively. The uncertainty between the two DIR methods were ranged -1.3 similar to 0.2% for all the investigated parameters of heart. There was minimal uncertainty of cardiac dose in DIR algorithms, meanwhile the intra-fraction variation was lager, and the interfraction variation was the largest uncertainty.