2889 - The Optimal Fractionated Pattern of Adjuvant Radiation for Patients with Adenocarcinoma of Cervix after Radical Surgery: 45Gy/25f vs. 50.4Gy/28f

Purpose/Objective(s): To compare the survival difference between 45Gy/25f and 50.4Gy/28f as the fractionated pattern for post-operative patients with adenocarcinoma of cervix (ADC) receiving adjuvant radiotherapy.

Materials/Methods: 237 ADC patients who received adjuvant radiotherapy after radical surgery from the Peking Union Medical College Hospital (PUMCH) between 2013 and 2023 were selected and analyzed. Patients who received adjuvant radiation after surgery were assigned into 45Gy/25f and 50.4Gy/28f group, respectively. The overall survival (OS) and Disease free survival (DFS) between two groups were compared before and after propensity scoring matching (PSM). Univariate and multivariate cox regression analysis were conducted to identify the independent risk factors for DFS of these patients. The risk factors identified from the multivariate cox regression analysis were incorporated into the construction of Recursive partitioning risk stratification analysis (RPA). The survival outcomes were compared between 45Gy/25f and 50.4Gy/28f group in different RPA-derived risk groups.

Results: The mode of 45Gy/25f was superior to 50.4Gy/28f in terms of 3-yr OS (HR=2.32, 95%CI: 1.02-5.27, P=0.039) and DFS (HR=1.84, 95%CI: 1.01-3.35, P=0.042) before PSM, while this superiority couldn't be maintained after PSM (OS: HR=1.61, 95%CI: 0.59-4.36, P=0.3; DFS: HR=1.37, 95%CI: 0.64-2.96, P=0.4). The pretreatment CA-125 level and depth of myometrial infiltration (DOI) were selected to construct the RPA risk classification. Three RPA-derived risk groups (RPA I-III) with distinct survival outcomes were identified (P<0.001). Moreover, 45Gy/25f pattern was observed to be more beneficial for 3-yr OS (HR=2.23, 95%CI: 1.47-3.06, P=0.029) and DFS (HR=2.88, 95%CI: 1.62-3.34, P=0.02) than 50.4Gy/28f in RPA II (middle risk) group, while no significant differences between 45Gy/25f and 50.4Gy/28f pattern was observed in RPA I (low risk) group and RPA III group (high risk) group (All P>0.05). The difference of two fractionated patterns in RPA I group should be further evaluated given the extremely small number of patients in RPA I group (n=35).

Conclusion: Three tiers of risk stratification system was constructed and the 45Gy/25f pattern was superiority to 50.4Gy/28f in RPA II (middle risk) group, while no significant difference was observed between two patterns in RPA III (high risk) group, which might demand more intensive dose pattern.