Voluntary versus ABC breath-hold in the context of VMAT for breast and locoregional lymph node radiotherapy including the internal mammary chain

Background: Deep-inspiration breath-hold (DIBH) reduces radiation dose to the heart in patients undergoing locoregional breast radiotherapy. In the context of tangential irradiation of the breast/ chest wall, a voluntary breath hold (vDIBH) technique has been shown to be as reproducible as a machine-assisted breath hold technique using the active breathing co-ordinator (ABC™, Elekta, Crawley, UK, ABC_DIBH). This study compares set-up reproducibility for vDIBH versus ABC_DIBH in patients undergoing volumetric-modulated arc radiotherapy (VMAT) for breast cancer, both with and without wax bolus. Method: Patients with breast cancer requiring pan regional lymph node VMAT +/− wax bolus in breath-hold were CT scanned in vDIBH and ABC_DIBH. Patients were randomised to receive one technique for fractions 1–7 and the other for fractions 8–15. Daily cone beam computed tomography (CBCT) was performed and registered to planning-CT using bony anatomy. Within-patient comparisons of mean daily chest wall position were made using a paired t-test. Population, systematic (∑) and random errors (α) were estimated. Intrafraction reproducibility was assessed by comparing chest wall position and diaphragm movement between consecutive breath holds on CBCT. Results: 16 patients were recruited. All completed treatment with both techniques (9 patients with wax bolus, 7 patients without). CBCT derived ∑ were 2.1–6.4 mm (ABC_DIBH) and 2.1–4.9 mm (vDIBH), α were 1.7–2.6 mm (ABC_DIBH) and 2.2–2.7 mm (vDIBH) and mean daily chest wall displacements (MD) were 0.0–1.5 mm (ABC_DIBH) and -0.1–1.6 vDIBH (all p non-significant). Chest wall and diaphragm position was equivalent between consecutive breath holds in ABC and vDIBH (median difference 1.0 mm and 0.8 mm respectively, non p significant) demonstrating equivalent intrafraction reproducibility. Conclusion: This study demonstrates that a simple voluntary breath hold technique is feasible in combination with VMAT (+/− bolus) and is as reproducible as ABC_DIBH with VMAT for the irradiation of the breast and axillary and IMC lymph nodes in breast cancer patients.