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

Abstract

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.

Keywords: breast neoplasms; breath holding; heart/radiation effects; radiotherapy; respiratory training.

Fig. 1

Training process and timetable of training, radiation therapy planning and treatment delivery. Boxes in top row show the interventions of coaching/training, CT simulation and verification simulation in relation to the intervening time intervals of DIBH home practice, wait time to treatment start and daily treatment course (shown in pink‐shaded arrow boxes). Corresponding duration of home practice, wait period and the treatment course are shown below pink‐shaded arrow boxes. Grey‐shaded boxes present details of coaching/training.

Fig. 2

Real‐time chestwall motion tracing for DIBH. Example of a typical DIBH tracing and Tracking Summary table from the Calypso tracking system is shown. Grey‐shaded areas indicate beam‐on status. Black tracing indicates the coordinate of the beacon, parameterized by time (s). The max‐excursion is the absolute most displacement from the set‐zero‐point (i.e. target position) during beam‐on times (grey shaded). Two step‐and shoot tangential beams are presented in this patient. The table shows a maximum chestwall excursion during beam‐on time of 3.4 mm (pink‐shaded value) in the inferior direction during this treatment fraction.

Fig. 3

Distributions of maximal excursion of the chestwall in any direction and in the individual AP, RL and SI directions in preparatory‐trained vs. non‐trained patients. Box‐and‐whisker plots represent the median (solid line), inter‐quartile range (IQR; box) and range of the excursions in each group. The whiskers extend up to 1.5 times the IQR from the box to the smallest and largest points. Data points beyond that range are shown explicitly. The “x” indicates the mean value in each group. No differences between the preparatory‐trained (_prepTrn/_extDIBH) and non‐trained (non‐Trn) groups were statistically significant (see Table 1).

Fig. 4

Distributions of the percentage of fractions where the chestwall excursion exceeds the 3‐mm tolerance threshold in preparatory‐trained vs. non‐trained patients. Box‐and‐whisker plots represent the median (solid line), inter‐quartile range (IQR; box) and range of the excursions in each group. The whiskers extend up to 1.5 times the IQR from the box to the smallest and largest points. Data points beyond that range are shown explicitly. The “x” indicates the mean value in each group. An asterisk indicates a statistically significant difference (P < 0.05) in beyond‐tolerance chestwall excursions between the preparatory‐trained (_prepTrn/_extDIBH) and non‐trained (non‐Trn) group (see also Table 1).

Fig. 5

Comparison of chestwall excursion longitudinally during the radiotherapy course in each direction in preparatory‐trained vs. non‐trained patients. The maximal excursions (max‐excursions) of the chestwall were averaged at each day of treatment. Error bars indicate one standard error of the mean. The average excursions within each week (fractions 1–5, 6–10 and 11–16) were compared between _prepTrn/_extDIBH and non‐Trn patient groups. The vertical dashed lines indicate the boundaries between weeks. In fraction 1–5 (first treatment week) max‐excursions in any direction and in the AP direction specifically were significantly lower in the _prepTrn/_extDIBH group than the non‐Trn group.