The dosimetric benefit of in‐advance respiratory training for deep inspiration breath holding is realized during daily treatment in left breast radiotherapy: A comparative retrospective study of serial surface motion tracking

INTRODUCTION: A novel approach of in‐advance preparatory respiratory training and practice for deep inspiration breath holding (DIBH) has been shown to further reduce cardiac dose in breast cancer radiotherapy patients, enabled by deeper (extended) DIBH. Here we investigated the consistency and stability of such training‐induced extended DIBH after training completion and throughout the daily radiotherapy course. METHODS: Daily chestwall motion from real‐time surface tracking transponder data was analysed in 67 left breast radiotherapy patients treated in DIBH. Twenty‐seven received preparatory DIBH training/practice ((prep)Trn) 1–2 weeks prior to CT simulation, resulting in an extended DIBH ((ext)DIBH) and reduced cardiac dose at simulation. Forty had only conventional immediate pre‐procedure DIBH instruction without (prep)Trn and without extended DIBH (non‐Trn group). Day‐to‐day variability in chestwall excursion pattern during radiotherapy was compared among the groups. RESULTS: The average of daily maximum chestwall excursions was overall similar, 2.5 ± 0.6 mm for (prep)Trn/(ext)DIBH vs. 2.9 ± 0.8 mm for non‐Trn patients (P = 0.24). Chestwall excursions beyond the 3‐mm tolerance threshold were less common in the (prep)Trn/(ext)DIBH group (18.8% vs. 37.5% of all fractions within the respective groups, P = 0.038). Among patients with cardiopulmonary disease those with (prep)Trn/(ext)DIBH had fewer chestwall excursions beyond 3 mm (9.4% vs. 46.7%, P = 0.023) and smaller average maximum excursions than non‐Trn patients (2.4 ± 0.3 vs. 3.0 ± 0.6 mm, P = 0.047, respectively). CONCLUSION: Similar stability of daily DIBH among patients with and without preparatory training/practice suggests that the training‐induced extended DIBH and cardiac dose reductions were effectively sustained throughout the radiotherapy course. Training further reduced beyond‐tolerance chestwall excursions, particularly in patients with cardiopulmonary disease.