MRI based analysis of organ at risk stability during prolonged voluntary Deep Inspiration Breath-Hold in prone and supine breast cancer radiotherapy

Background and Purpose Deep inspiration breath-hold (DIBH) is commonly used in breast cancer radiotherapy to reduce radiation exposure to the heart and lungs. Recent techniques incorporating oxygen supplementation and hyperventilation have enabled DIBHs exceeding 2.5 minutes. However, data on internal organ st ability during prolonged breath-holds (L-DIBH) remain limited. Materials and Methods In this prospective observational physiological study, ten healthy female volunteers performed two L-DIBHs (2 minutes 8 seconds each) in both prone and supine positions, following a validated hyperventilation and oxygenation protocol. Serial 3D MRI scans were acquired every 16 seconds during each L-DIBH to assess positional stability of the heart, lungs, and left-sided breast. Cumulative distance–volume histograms (cDiVHs) were used to evaluate spatial relationships between organs and quantify internal displacement over time. Results 319 high-quality 3D MRI series were analysed. cDiVHs demonstrated consistent organ positions across timepoints and sessions. While left breast position remained stable throughout all L-DIBHs, minor but statistically significant heart displacement was observed during each L-DIBH increasing over time, more pronounced in the prone position than supine. Conclusion L-DIBHs of 2 minutes and 8 seconds are achievable and demonstrate stability in left breast positioning, with minimal movement of adjacent internal organs. Small but progressive shifts of the portion of the heart nearest the breast were detected, particularly in prone positioning. Advances in Knowledge To account for these minimal displacements during L-DIBH, asymmetrical safety margins around the heart of 3 mm in prone and 2 mm in supine positions may be appropriate.