A three day coaching protocol for deep inspiration breath hold in left breast radiotherapy using active breathing control

The deep inspiration breath-hold (DIBH) technique is recommended for left-sided breast radiotherapy to reduce heart dose exposure. However, this technique introduces uncertainties due to possible anatomical variations across successive breath-holds, requiring patient coaching to ensure reproducibility. This study aims to establish an objective coaching framework to optimize DIBH effectiveness and achieve the reproducibility of chest anatomy in left-sided breast radiotherapy. This study implemented a three-day DIBH coaching protocol using the Active Breathing Coordinator (ABC) system (Elekta AB, Sweden), with particular emphasis on the breath-hold threshold and the lung volume difference from CT images. The former was a manually configured parameter in the ABC system that reflected the stability of patient's respiratory maneuvers during coaching. The latter was used to quantify the DIBH reproducibility. Quantitative analysis demonstrated that for the 9 patients who exhibited fluctuations in their breath-hold threshold, continued coaching successfully enabled them to achieve stability. Another 14 patients maintained a consistent breath-hold threshold throughout the entire coaching process. Only one patient showed deterioration in this parameter. Additionally, the breath-hold threshold showed significant positive correlations with DIBH lung volumes: left lung (r = 0.638, p = 8.028 × 10^-4), right lung (r = 0.647, p = 6.284 × 10^-4). Regarding reproducibility of DIBH, 78.3% (18/23) and 73.9% (17/23) of patients maintained ≤ 0.1 L difference between two DIBH scans for left and right lung volumes, respectively, with no patient exceeding a relative lung volume difference of 0.2. Ultimately, 96% (24/25) of the patients achieved highly reproducible DIBH after coaching. In this study, the individualized determination of breath-hold thresholds was critical in ABC-assisted DIBH left breast radiotherapy. Through a standardized process, it objectively identified which patients required additional assistance and which were prepared to proceed. After coaching, the observed differences in lung volume between successive breath-holds were minimal, indicating excellent reproducibility of the chest anatomy positioning and enabling more precise left-sided breast radiotherapy.