Effect of Simultaneous Integrated Boost Intensity Modulated Radiation Therapy (SIB-IMRT) and Non-Operative Strategy on Outcomes of Distal Rectal Cancer Patients with Clinically Positive Lateral Pelvic Lymph Node

Shuai Li,1,* Jianhao Geng,1,* Lin Wang,2,* Huajing Teng,1 Zhilong Wang,3 Xianggao Zhu,1 Yangzi Zhang,1 Hongzhi Wang,1 Yongheng Li,1 Yong Cai,1 Aiwen Wu,2 Weihu Wang1 1Department of Radiation Oncology, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), Peking University Cancer Hospital and Institute, Beijing 100142, People’s Republic of China; 2Department of Surgery, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Peking University Cancer Hospital & Institute, Beijing 100142, People’s Republic of China; 3Department of Radiology, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Peking University Cancer Hospital & Institute, Beijing 100142, People’s Republic of China*These authors contributed equally to this workCorrespondence: Weihu Wang; Aiwen Wu Tel +8610-88196087; +8610-88196086Email wangweihu88@163.com; wuaw@sina.comBackground: We aimed to analyze the effect of simultaneous integrated boost intensity modulated radiation therapy (SIB-IMRT) and non-operative treatment on the clinical outcomes of distal rectal cancer patients exhibiting clinically positive lateral pelvic lymph nodes (LPLNs).Methods: We reviewed the medical records of patients diagnosed as having distal rectal adenocarcinoma with clinically positive LPLNs (≥ 7 mm, with irregular borders or mixed signal intensity) using primary pelvic magnetic resonance imaging (MRI). These patients had received SIB-IMRT-based neoadjuvant chemoradiotherapy (NCRT) and non-operative treatment according to the heterogeneity of the disease or personal preference. Chi-square tests were used to compare data between the two groups. Progression-free survival (PFS) and local regrowth were evaluated using the Kaplan-Meier method.Results: Between 2016 and 2019, we analyzed 75 patients diagnosed as having clinically positive LPLNs using primary MRI. SIB-IMRT was delivered to the planning positive LPLNs (PGTVn) at a total dose of 56– 60 Gy. After NCRT, 23 patients underwent non-operative treatment. Among these patients, the median short axis of LPLNs was 8 mm (range: 7– 21 mm). Fifteen patients were categorized into the mesorectal fascia (MRF)-positive group. The median follow-up duration for these patients was 19.8 months, and no patient exhibited LPLN regrowth. The 2-year PFS rate was 85.6% for non-operative patients, 74.6% for operative patients, and 90.0% for the pathological complete response (pCR) subgroup. Eighteen patients who underwent non-operative treatment were included in the clinical complete response (cCR) subgroup. The 2-year PFS and local regrowth rates in this group were similar to those in patients with clinically negative LPLN who achieved cCR. During NCRT, 21 (28.0%) patients experienced grade 2– 3 acute reversible toxicity.Conclusions: SIB-IMRT could eliminate metastases in LPLNs in a safe and effective manner, and non-operative strategies may be promising for cCR patients.Keywords: rectal cancer, simultaneous integrated boost intensity modulated radiation therapy, lateral pelvic lymph nodes, disease-free survival