Evaluating the Implementation of Fan-Beam CT-Guided Online Adaptive Re-planning in Definitive Cervical Cancer Radiotherapy

Shuai Sun ¹ Xinyue Gong ^1,2 Yongguang LIANG ¹ Yuliang Sun ¹ Dan Que ³ Yangchun Xie ⁴ Shumeng He ⁵ Lei He ¹ Hao Liang ¹ Yijun Wang ¹ Xinyi Wu ⁶ Cheng Wang ⁶ Bo Yang ¹ Jie Qiu ¹ Ke Hu ^1* Fuquan ZHANG ^1*

• ¹ Peking Union Medical College Hospital (CAMS), Beijing, China
• ² Chinese Academy of Medical Sciences and Peking Union Medical College, Dongcheng, Beijing Municipality, China
• ³ Third Affiliated Hospital of Chongqing Medical University, Chongqing, Sichuan Province, China
• ⁴ Second Xiangya Hospital, Central South University, Changsha, Hunan Province, China
• ⁵ Beijing United Imaging Intelligent Imaging Technology Research Institute, Beijing, Beijing Municipality, China
• ⁶ Shanghai United Imaging Healthcare Co., Ltd., Shanghai, China

Background: This study aims to investigate the feasibility of fan-beam computed tomography (FBCT)-guided online adaptive radiotherapy (oART) in radical radiotherapy for cervical cancer.Methods: Ten patients who underwent radical radiotherapy for cervical cancer were enrolled in this study. All patients received external beam radiation therapy (EBRT) with a prescription dose of 50.4 Gy/28f, and daily oART with FBCT guidance was performed. Dosimetric analysis was conducted on 278 fractions, comparing the adaptive and scheduled plans. The γ passing rate was measured through in-vivo dose monitoring during treatment, using a 3%/3mm gamma criterion with an 88% threshold for alerts. The time invested in the oART workflow was recorded at each step. Acute toxicities were classified following the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0.Results: The adaptive plans demonstrated a dosimetric advantage in target coverage and/or organs at risk (OARs) sparing across all 278 fractions. Compared to the scheduled plan, the adaptive plan showed improved dose received by 95% (D95) of planning target volume (PTV), conformity index (CI), and homogeneity index (HI) (P<0.001). Among the three PTVs, the PTV of uterus (PTV_U) benefited most from dosimetric improvements in the adaptive plan, followed by the PTV of cervix, vagina, and parametrial tissues (PTV_C), while the PTV of lymph node (PTV_N) exhibited the least enhancement. For OARs, the adaptive plan achieved reductions in the dose to the most irradiated 2 cm³ volume (D2cc) for the rectum, bladder, and small intestine (P<0.001). For patients with ovarian conservation, the dose to the 50% volume (D50) and the mean dose of the bilateral ovaries were decreased (P<0.001). The mean γ passing rate across all fractions was 99.24%. The mean duration of the oART workflow was 22.82±3.61 min, with auto-segmentation & review (44.40%) and plan generation & evaluation (22.02%) being the most time-intensive steps. The incidence of Grade 1-2 acute non-hematological toxicity was 60%, with no cases of Grade 3 or higher observed.Conclusions: The implementation of FBCT-guided oART in radical radiotherapy for cervical cancer was feasible. This approach has shown significant improvements in dose distribution and the potential to provide clinical benefits by reducing acute toxicity.