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In the context of adjuvant left breast radiotherapy, collateral cardiac irradiation is associated with increased cardiovascular morbidity. By reducing the heart and the ipsilateral lung doses, deep inspiration breath-hold (DIBH) has thus become a standard-of-care. Different strategies have been developed either to optimize the breast repositioning accuracy during successive DIBH e.g. surface guided radiation therapy (SGRT) and/or to improve organs-at-risk (OARs) sparing e.g. prone position, continuous positive airway pressure (CPAP). These DIBH enhancements can potentially be coupled by mechanically-assisted and non-invasive ventilation (MANIV). Indeed, MANIV allows DIBH to be faithfully replicated with a large lung inflation by periodically imposing the same positive pressure for a predefined duration. The objective of the present study was therefore to test our research hypothesis by comparing, in real treatment conditions, voluntary DIBH guided by SGRT and MANIV-induced DIBH in supine position.

A randomized, non-blinded, multicenter and single-institution non-inferiority trial was conducted (NCT04457102 on ClinicalTrials.gov). Sixty-six patients eligible for adjuvant left whole-breast radiotherapy in supine position were  assigned in a (1:1) ratio between mechanically-induced DIBH (MANIV-DIBH arm) and voluntary DIBH guided by SGRT (sDIBH arm). The study flow chart is shown in Figure 1. In the sDIBH arm, treatment beam was delivered in 20 seconds DIBH during which the patient received oral instructions from the operator to adjust the breast position based on SGRT. In contrast, the breast position was simply monitored by SGRT in the MANIV-DIBH arm. The treatment worflow of the MANIV-DIBH arm is illustrated in Figure 2. The co-primary endpoints were positional breast stability and reproducibility with a non-inferiority margin of 1 mm.  Stability corresponded to the average intra-DIBH shifts, while reproducibility referred to the mean breast deviation during DIBH relative to a daily reference breast surface. Secondary endpoints were dose to OARs, tolerance and treatment time. Given the use of different fractionation schedules within the study, dosimetric comparisons was performed on treatment plans with a prescription of 15 x 2.67 Gy without boost.

Submillimeter differences in positional breast reproducibility and stability were found between both arms. (p < 0.001 for non-inferiority). The left anterior descending artery near-max dose (14,6±12,0 Gy vs. 7,7±7,1 Gy, p=0,018) and mean dose (5,0±3,5 Gy vs. 3,0±2,0 Gy, p=0,009) were significantly improved in the MANIV-DIBH arm. The same applied for the V5Gy of the left ventricle (2,4±4,1 % vs. 0,8±1,6 %, p=0,001) as well as for the left lung V20Gy (11,4±2,8 % vs. 9,7±2,7 %, p=0,019) and V30Gy (8,0±2,6 % vs. 6,5±2,3 %, p=0,0018). Tolerance and treatment time were comparable.

MANIV provides better OARs sparing while reaching the irradiation accuracy of SGRT.