# Impact of variation in voluntary moderate deep inspiration breath hold on the 3D dose distribution in breast cancer radiotherapy

## TL;DR

This study shows that voluntary deep breath holds during breast cancer radiotherapy are feasible without visual guidance, with minimal impact on radiation dose accuracy.

## Contribution

The study demonstrates the feasibility of using voluntary moderate deep inspiration breath hold without visual feedback in breast cancer radiotherapy.

## Key findings

- 61% of breath holds exceeded a 3 mm window, but dose deviations were minimal.
- Heart and lung doses remained within clinical limits despite variations.
- Minor deviations in V95% of the whole breast CTV were observed but not clinically significant.

## Abstract

•Variations were assessed using SGRT vmDIBH without visual coaching in 21 patients.•61% of BHs exceeded a 3 mm gating window, but dose deviations were minimal.•All mean heart and lung doses remained within clinical limits.•Findings support the feasibility of vmDIBH without continuous visual feedback.

Variations were assessed using SGRT vmDIBH without visual coaching in 21 patients.

61% of BHs exceeded a 3 mm gating window, but dose deviations were minimal.

All mean heart and lung doses remained within clinical limits.

Findings support the feasibility of vmDIBH without continuous visual feedback.

Determination of impact of variations during voluntary moderately deep inspiration breath hold (vmDIBH) on doses to organs at risk (OAR) and target coverage in patients undergoing radiotherapy (RT) for left-sided breast cancer (BC).

We recorded vmDIBH-breathing signals using a Surface Guidance system, without visual coaching, in 21 BC patients. In 13 patients, cone-beam CT (CBCT) scans were acquired with vmDIBH, immediately after treatment delivery. A 3D dose recalculation was performed on CBCT, cranio-caudally stitched with the planning CT for full dose evaluation. Mean Heart Dose (MHD), Mean Lung Dose (MLD) and V95% of the clinical target volume (CTV) were calculated. Relationships between vmDIBH level, stability and differences in Dose-Volume Histogram (DVH) parameters were analysed using linear regression and Mann-Whitney U-tests.

Of 150 recorded vmDIBHs, 39% of the breath-holds were within a predefined 3 mm gating window. The average deviation from this window was 0.6 mm (SD 1.9 mm), with the mean value just outside predefined boundaries. All recalculated CBCTs (n = 95) met predefined DVH criteria for MHD, MLD, and V95% of tumourbed CTV. The V95% of the whole breast CTV showed minor deviations from the planned dose (mean delta V95%: −0.8%, SD 1.6%). For patients with excursions beyond the 3 mm window, average differences were 1.43% in V95%-CTV, 0.02 Gy in MHD, and 0.05 Gy in MLD.

Only small breathing excursions beyond 3 mm were observed during vmDIBH without visual coaching, not resulting in clinically relevant CTV Underdosage with MHD and MLD remaining within tolerance.