2745 - Dosimetric Benefit and Clinical Feasibility of Deep Inspiratory Breath-Hold and Volumetric Modulated Arc Therapy Based Postmastectomy Radiotherapy for Left-Sided Breast Cancer

S. J. Wang¹, H. Jing¹, Y. Zhai¹, W. Zhang¹, S. Chen¹, S. Qin¹, H. Fang¹, Y. Tang², Y. Song¹, Y. Liu³, B. Chen¹, S. Qi¹, Y. Tang³, N. Lu¹, Y. LI⁴, and S. Wang³; ¹Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, ²GCP center/Clinical research center, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, ³State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College (PUMC), Beijing, China, ⁴State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC), Beijing, China

Purpose/Objective(s): To evaluate the domestric benefits and reproducibility of deep inspiratory breath-hold (DIBH) technique combined with volumetric modulated arc therapy (VMAT) in left-sided postmastectomy radiotherapy (PMRT); and to quantify variations in heart position and dose during DIBH treatment. Materials/

Methods: Eligible patients with left-sided breast cancer who received DIBH-based PMRT were prospectively included. Chest wall, supra/infraclavicular fossa, and/or internal mammary node irradiation (IMNI) were planned with a prescription dose of 43.5 Gy in 15 fractions. VMAT plans were designed on free breathing (FB)- and DIBH-CT scans to compare the dosimetric parameters in heart, left anterior descending artery (LAD) and lung. Cone-beam computed tomography (CBCT) scans were performed before and after treatment to evaluate the inter- and intra-fractional setup errors. The heart position and dose variations during DIBH treatment were estimated by the fusion of CBCT scans and DIBH-CT scans.
Results: Twenty consecutive patients were included and completed the DIBH treatments without interruption, of whom 10 patients received IMNI. A total of 193 pre-treatment and 39 pairs pre- and post-treatment CBCT scans were analyzed. The D_mean, D_max, and V_5-40 of the heart, LAD, and left lung were significantly lower in DIBH techniques compared with FB (p < 0.05 for all), except for V5 of LAD (p = 0.167). The cardiopulmonary dosimetric benefits were retained with IMNI or not. Moreover, the inter- and intra-fractional setup errors were < 0.3 cm; and the overall estimated PTV margins were < 1.0 cm. During DIBH treatment, the mean dice similarity coefficient of heart position and the mean ratio of heart D_mean between CBCT scans and DIBH-CT plans was 0.95 (0.88-1.00) and 100% (70.6%-119.5%), respectively.
Conclusion: DIBH-VMAT could effectively reduce the cardiopulmonary doses with acceptable reproducibility and stability in left-sided PMRT regardless of IMNI.