Helical tomotherapy with a complete-directional-complete block technique effectively reduces cardiac and lung dose for left-sided breast cancer

Objectives: To evaluate the feasibility and optimal restricted angle of the complete-directional- complete block (CDCB) technique in helical tomotherapy (HT) by including regional nodal irradiation (RNI) with the internal mammary node (IMN) in left-sided breast cancer. Methods: Ten left-sided breast cancer patients treated with 50 Gy in 25 fractions were compared with five-field intensity-modulated radiation therapy (5F-IMRT) and six types of HT plans. In the HT plans, complete block (CB), organ-based directional block (OBDB) and CDCB with different restricted angles were used. Results: The conformity index (CI) between the CDCB0,10,15,20 and 5F-IMRT groups was similar. Compared to CB, OBDB and 5F-IMRT, CDCB20 resulted in a decreased ipsilateral mean lung dose. The low-dose region (V5) of the ipsilateral lung in OBDB (84.0%) was the highest among all techniques (p < 0.001). The mean dose of the heart in CB was significantly reduced (by 11.5-22.4%) compared with other techniques. The V30 of the heart in CDCB20 (1.9%) was significantly lower than that of CB, OBDB and 5F-IMRT. Compared to the mean dose of the left anterior descending (LAD) artery of 5F-IMRT (27.0 Gy), CDCB0, CDCB10, CDCB15, CDCB20 and OBDB reduced the mean dose effectively by 31.7%, 38.3%, 39.6%, 42.0 and 56.2%, respectively. Considering the parameters of the organs-at- risk (OARs), CDCB10,15,20 had higher expectative values than the other techniques (p = 0.01). Conclusions: HT with the CDCB technique is feasible for treating left-sided breast cancer patients. The CDCB10- 20 techniques not only achieved similar planning target volume coverage, homogeneity and dose conformity but also allowed better sparing of the heart and bilateral lungs. ? 2020 The Authors.