Dosimetric optimization and clinical feasibility of the block technique in helical tomotherapy for bilateral breast cancer.

In this study, we aimed to investigate the effects of different block combinations in helical tomotherapy (HT) on the dose distribution in the target volume, protection of the organs at risk (OARs), and treatment efficiency in patients with bilateral breast cancer (BBC), and to provide a dosimetric basis for the selection of individualized radiotherapy plans. Clinical data of 21 patients with BBC without distant metastasis, who underwent initial radiotherapy from January 2021 to September 2024, were retrospectively analyzed. Based on the properties of blocks-complete block (CB), directional block (DB), no block (NB) and their positions: spinal cord and bilateral lungs, 5 block combination plans were designed for each patient: SNLN (spinal NB/lung NB), SCLN (spinal CB/ lung NB), SCLC (spinal CB/lung CB), SNLC (spinal NB/lung CB), SDLD (spinal DB/lung DB). The dosimetric parameters for the target and OARs, treatment plan monitor units (MUs), and beam-on times (BOTs) were compared. All 5 plans met the clinical requirements for the target, V, V, homogeneity index, and conformity index with no statistically significant difference (p > 0.05). The lung CB significantly reduced the heart and lung irradiation doses. The spinal CB reduced the maximum dose to the spinal cord in the supraclavicular lymph node drainage area from 25 to 35 Gy to 4-9 Gy (p < 0.01). The lung CB group (Plans SCLC,SNLC) increased the BOT by 35% (p < 0.01) and MU by 2596 to 3060 compared to the lung NB group (Plans SNLN,SCLN). The DB (Plan SDLD) group balanced the OAR sparing and treatment efficiency; cardiopulmonary doses in the DB group were between those in the lung CB and NB groups (p < 0.01). The HT block technique significantly enhanced OAR protection. Lung and spinal CB maximized cardiopulmonary and spinal cord dose reductions at the expense of prolonging the BOT and MU. DB could be an alternative strategy for patients requiring a shorter BOT.