Effect of external beam radiotherapy on hepatic parenchymal resection rate.

e16315 Background: The hepatic parenchymal resection rate (HPRR), defined as the percentage of tumor-bearing liver volume relative to total liver volume, is a critical preoperative evaluation factor for surgical resection in patients with primary liver cancer (PLC). A higher HPRR indicates an increased risk of postoperative liver failure. Previous studies have demonstrated that Yttrium-90 transarterial radioembolization (TARE) can reduce HPRR. However, the effect of external beam radiotherapy (EBRT) on hepatic volume changes and HPRR remains unclear. This study aimed to investigate whether EBRT could reduce HPRR and identify key factors influencing HPRR changes following radiotherapy. Methods: Patients with PLC who underwent radiotherapy between June 2018 and December 2022 were included in this study. Eligibility criteria required patients to have undergone abdominal CT or MRI imaging within 1 month before radiotherapy and within 6 months after completing radiotherapy. HPRR was calculated before and after radiotherapy. A reduction in HPRR was defined as a post-radiotherapy HPRR less than the pre-radiotherapy HPRR. Independent predictors of HPRR reduction (p < 0.05) were identified using logistic proportional hazards regression models. Results: A total of 178 patients (predominantly Barcelona Clinic Liver Cancer stage C) were included in the final analysis. 173 patients (97.2%) experienced shrinkage of the tumor-bearing liver following EBRT, accompanied by a reduction in HPRR compared to baseline. The median reduction in tumor-bearing liver volume was 27.45% (IQR: 14.40%-42.55%), with 110 patients experiencing a reduction exceeding 20%. 127 patients (71.3%) achieved a reduction in HPRR. Further univariate logistic regression analysis revealed that a larger radiation dose (OR = 1.71, 95% CI: 1.21-2.41, P < 0.01) and a higher radiotherapy dose-to- radiation frequency-to-PTV ratio (OR = 10.01, 95% CI: 2.50-40.08, P < 0.01) were significantly associated with a reduction in HPRR. Furthermore, compared to male patients, female patients (OR = 4.53, 95% CI: 1.31-15.63, P = 0.02) showed a more pronounced tendency towards reduced HPRR. Multivariate logistic regression analysis confirmed that radiation dose (OR = 1.55, 95% CI: 1.06-2.26, P = 0.03), radiotherapy dose-to- radiation frequency-to-PTV ratio (OR = 9.19, 95% CI: 2.20-38.38, P < 0.01), and female sex (OR = 5.24, 95% CI: 1.45-18.91, P = 0.01) were independent predictive factors for the reduction in HPRR after treatment. Conclusions: EBRT significantly reduces HPRR by inducing tumor-bearing liver shrinkage, providing a feasible preoperative strategy for patients with primary liver cancer. Independent factors include a larger radiation dose and a higher radiotherapy dose-to-radiation frequency-to-PTV ratio. In addition, a more pronounced treatment response was observed in female patients.