Comparative Analysis of OAR Doses in Whole-Breast RT: Prone vs Supine Positions with DIBH

Overview

This prospective subgroup analysis compared organ-at-risk (OAR) doses during whole-breast irradiation using supine free-breathing (FB), supine deep inspiration breath-hold (DIBH), and prone positioning. The study included both left- and right-sided breast cancer patients and evaluated dosimetric parameters for the heart, lungs, and other critical structures.

Background

Whole-breast irradiation after breast-conserving surgery improves breast cancer-specific survival but exposes organs at risk such as the heart and lungs to radiation, increasing risks of cardiac injury and secondary cancers. Techniques like deep inspiration breath-hold (DIBH) and prone positioning have been developed to reduce these doses. While DIBH is favored for reducing mean heart dose in left-sided breast cancer, prone positioning reduces lung exposure. However, direct dosimetric comparisons between these techniques, especially including right-sided breast cancer, remain limited.

Data Highlights

The study analyzed dose-volume histogram parameters including mean heart dose (MHD) and partial volume doses at multiple thresholds (V1 to V40 Gy) for the heart, left anterior descending artery (LAD), right coronary artery (RA), ipsilateral lung, and contralateral breast. Statistical analyses compared these parameters across three treatment positions: supine free-breathing, supine DIBH, and prone positioning.

Key Findings

• Supine DIBH significantly reduced mean heart dose (MHD) compared to supine free-breathing and prone positions, particularly in left-sided breast cancer patients.
• Prone positioning effectively decreased ipsilateral lung dose volumes compared to both supine techniques, lowering potential lung toxicity risk.
• DIBH provided superior cardiac sparing without compromising target coverage, especially for left-sided tumors.
• Prone positioning was beneficial in reducing lung exposure for both left- and right-sided breast cancer patients.
• Contralateral breast and other OAR doses were maintained within acceptable limits across all techniques.
• Patient selection for DIBH required adequate cardiopulmonary function and ability to maintain stable breath-hold, while prone positioning was feasible for most patients.

Clinical Implications

Clinicians should consider supine DIBH for optimal cardiac dose reduction in left-sided breast cancer patients, especially those with good breath-hold capacity. Prone positioning offers a valuable alternative to reduce lung doses and may be particularly advantageous for patients with right-sided breast cancer or those unable to perform DIBH. Individualized treatment planning incorporating these techniques can enhance organ preservation without compromising tumor coverage.

Conclusion

This prospective analysis demonstrates that supine DIBH and prone positioning each offer distinct dosimetric advantages in whole-breast irradiation, with DIBH favoring cardiac sparing and prone positioning reducing lung exposure. Tailoring radiotherapy technique based on tumor laterality and patient capability can optimize organ-at-risk protection.

References

1. Wang SL et al. 2021 -- Hypofractionated fractionation scheme in breast radiotherapy
2. RTOG Guidelines 2010 -- Target and OAR contour delineation
3. ClinicalTrials.gov NCT05609058 -- Prospective observational study on breast radiotherapy positions