Given the increased risk of cardiac toxicity with higher doses, cardiac sparing is crucial for left-sided breast cancer patients. Deep inspiration breath hold (DIBH) is one approach, but its reproducibility is questioned. This study evaluates the reproducibility of DIBH with an active breathing coordinator (ABC) device, focusing on its dosimetric impact in maintaining consistent cardiac sparing for patients undergoing partial breast irradiation (PBI).

Thirty-three patients undergoing PBI with a prescription dose of 30 Gy in five fractions were randomly selected. Each patient was treated with 6 MV photons using volumetric modulated arc therapy (VMAT) with DIBH using an ABC device. Prior to each fraction, kilo-voltage cone beam computed tomography (kV-CBCT) images were acquired to assess inter-fractional heart motion. Contours of the whole heart and left anterior descending artery (LAD) were transferred from the planning CT to CBCTs and back, using rigid alignment and isocentre shifts to represent treatment positions. Agreement between delivered and planned doses assessed DIBH reproducibility.

Throughout the entire treatment course, changes in mean and maximum cardiac doses were less than 16·4 cGy and 264·8 cGy, respectively. Changes in mean and maximum LAD doses were less than 54·0 cGy and 160·2 cGy, respectively. Overall, the mean cardiac dose increased by 2·4 ± 6·6 cGy, and the maximum by 23·3 ± 58·0 cGy. The mean LAD dose increased by 4·8 ± 18·5 cGy, and the maximum by 17·0 ± 51·0 cGy.

DIBH can be effectively reproduced with the ABC device, limiting inter-fractional cardiac dose changes.