2753 - Radiotherapy Quality Assurance of the Ongoing Potential Phase III Randomized Controlled Trial Investigating the Role of Internal Mammary Lymph Node Irradiation for Breast Cancer: An Individual Case Re

X. Zhao¹, H. Fang¹, W. F. Yang², Y. Zhong³, Q. Zhong⁴, H. Jing¹, X. N. Yan¹, K. Men¹, Z. Hu¹, L. Dong⁵, H. F. Wu⁶, X. H. WANG⁷, J. Tie⁸, X. Hou⁹, L. Zhao¹⁰, Y. LU¹¹, J. Zhang¹², J. Jin¹³, J. Ma¹⁴, X. Du¹⁵, N. Zhang¹⁶, Y. X. Li¹, and S. Wang¹⁷; 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, ²Department of Radiation Oncology, Affiliated Taizhou hospital of Wenzhou Medical University, Taizhou, China, ³Department of Radiation and Medical Oncology, Zhongnan Hospital of Wuhan University, Wuhan, China, ⁴Department of Radiation Onoclogy, Beijing Hospital, National Center of Gerontology, Institute of Geriatric Medicine, Chinese Academy of Medical Sciences, Beijing, China, ⁵Department of Radiation Oncology, The First Hospital, Jilin University, Changchun, China, ⁶Department of Radiation Oncology, Jilin Cancer Hospital, Changchun, China, ⁷Department of Radiochemotherapy, People’s Hospital of Tangshan City, Tangshan, China, ⁸Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Department of Radiation Oncology, Peking University Cancer Hospital and Institute, Beijing, China, ⁹Department of Radiation Oncology, Peking Union Medical College Hospital, Chinese Academy of medical Sciences & Peking Union Medical College, Beijing, China, ¹⁰Department of Radiation Oncology, Xijing Hospital, Fourth Military Medical University., Xi’an, China, ¹¹Department of Radiation Oncology, Cancer Hospital of Henan Province, Zhengzhou, Henan, China, ¹²Department of Radiation Oncology, Forth Hospital of Hebei Medical University, Shijiazhuang, China, ¹³Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China, ¹⁴6. Department of Radiation Oncology, Jiangsu Province Hospital of Chinese medicine, Affiliated Hospital of Nanjing University of Chinese Medicine, Nanjing, Jiangsu, China, ¹⁵Department of Thoracic Radiotherapy, Zhejiang Cancer Hospital, Hangzhou Institute of Medicine (HIM), Chinese Academy of Sciences, Hangzhou, Zhejiang, China, ¹⁶2. Department of Radiation Oncology, Cancer Hospital of China Medical University, Liaoning Cancer Hospital & Institute, Shenyang, Liaoning, China, ¹⁷State 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

Purpose/Objective(s): POTENTIAL is an ongoing, prospective, phase III randomized trial investigating the effects of post-mastectomy internal mammary nodal irradiation (IMNI) on the prognosis of high-risk breast cancer patients with positive axillary nodes. The present study aimed to assess for protocol compliance by performing an individual case review (ICR). Materials/

Methods: At the onset of the trial, all participating institutions were invited to submit the radiotherapy plans of their first 10 patients. Measured parameters included radiotherapy techniques, dosimetric parameters of the target volumes and the organs at risk (OARs), and the effects of IMNI on IMN and cardiopulmonary dose exposure. This procedure was repeated at the middle of the accrual period, sixteen participating institutions were asked to submit data on 4 randomly selected cases (2 in the IMNI and 2 in the no IMNI group, respectively) for the second ICR. The protocol compliance rates of the second ICR-plans were compared with the first one.
Results: The first and second ICR involved 160 and 64 plans from 16 participating institutions, respectively. Hypofractionated (HFRT) and conventional fractionated (CFRT) regimes were involved in 44.2% and 45.8% of the 224 plans, respectively. Volumetric-modulated arc therapy (VMAT) (54.0%) and multi-beam intensity-modulated radiotherapy (IMRT) (40.2%) techniques were most commonly employed, followed by combined IMRT/VMAT and electron beam therapy (4.9%) and 3-D CRT and IMRT system (0.9%). The dose coverage for all planning target volumes (PTV) was considered acceptable in 73.1 – 95.0% of the first ICR plans and 78.1 – 95.3% of the second ICR plans, respectively. The compliances of OAR dose constraints were acceptable in 88.1 – 100.0% of the first ICR plans and 93.8 – 100% of the second ICR plans, respectively. The protocol compliance rates of the dose coverage for PTV and the dose constraints for most OARs were slightly improved in the second ICR compared with those in the first ICR, but the differences were not significant. In the IMNI group, 90.5-91.4% of PTV of IMN received the prescribed dose, while in the no IMNI group, 32.8 – 40.4% of PTV of IMN received the prescribed dose. IMNI was associated with significantly higher heart dose and ipsilateral pulmonary dose exposure compared with no IMNI (P <0.05).
Conclusion: Overall, acceptable compliance to the protocol of the POTENTIAL trial was observed. Findings of this ICR provided valuable insights into the current radiation techniques for IMNI, and the quality of radiotherapy planning in clinical practice. The evaluation of the second ICR plans showed that unacceptable protocol deviations still existed, emphasizing the importance of the continuous monitoring. The unintentionally doses to IMN in the no IMNI group treated with complexed intensity modulated technique are innegligible.