Reproducibility and stability of deep inspiration breath hold and free breath in breast radiotherapy based on real-time 3-dimensional optical surface imaging system

Background The aim of this study was to evaluate the inter-fraction reproducibility and intra-fraction stability of breast radiotherapy using deep-inspiration breath hold (DIBH) and free breathing (FB) based on an optical surface imaging system (OSIS). Methods Seventeen patients (510 breath-hold sessions) treated using a field-in-field (FiF) technique and twenty patients (600 breath-free sessions) treated with a volume-modulated arc therapy (VMAT) technique were included in this retrospective study. All the patients were positioned with the guidance of CBCT and OSIS, and also monitored with OSIS throughout the whole treatment session. Eight setup variations in three directions were extracted from the treatment reports of OSIS for all sessions and were subsequently manually introduced to treatment plans, resulting in a total of 296 perturbed plans. All perturbed plans were recalculated, and the dose volume histograms (DVH) for the target and organs at risk (OAR) were analyzed. Results The OSIS and CBCT for both DIBH and FB treatments showed a good agreement of less than 0.12 cm in each direction. The intra-fraction setup errors during DIBH were − 0.06 ± 0.07 cm, 0.12 ± 0.15 cm, and 0.12 ± 0.12 cm in the lateral, longitudinal, and vertical directions, respectively; for FB, the errors were − 0.02 ± 0.12 cm, 0.08 ± 0.18 cm, and 0.14 ± 0.20 cm, respectively. For the target, DIBH plans were more sensitive to positioning errors; the mean deviations in D ₉₅ for CTV were 39.78 Gy-40.17 Gy for DIBH and 38.46 Gy-40.52 Gy for FB, respectively. For the OARs, the mean deviations—V ₁₀ , V ₂₀ , and D _mean to the heart; V ₅ , V ₂₀ , and D _mean to the ipsilateral lung; and D _mean to the breast—were lower for the FB plan compared with the DIBH plan. Conclusion SGRT can be an important tool for inter-fraction patient positioning and intra-fraction patient respiratory motion management in DIBH and FB breast cancer radiotherapy. The FB technology has greater possibility for the undercoverage of the target volume, while DIBH technology is more likely to result in increases in dose to organs at risk, especially the lung, heart, and breast. Furthermore, the tolerance of optical surface imaging systems could be reduced, indicating a potential method to reduce the dose delivery uncertainty caused by the patient’s respiratory motion.