(P 338) PREOPERATIVE RADIATION THERAPY IS NOT ASSOCIATED WITH ADVERSE POSTOPERATIVE OUTCOMES IN PATIENTS WITH RETROPERITONEAL SARCOMA

Objective: The role of preoperative radiation therapy (preop RT) in the management of retroperitoneal sarcomas (RPS) remains controversial. Due to the radical nature of surgery for RPS, short-term postoperative complication rates are relatively high, and the potential for worse postoperative outcomes with preoperative RT remains a legitimate concern. While median preoperative radiation doses typically range between 45 Gray (Gy) and 54 Gy in most studies on perioperative outcomes in RPS, protocols at our institution include high preoperative radiation doses up to 63 Gy to the high-risk margin. We sought to examine the 30-day morbidity and 90-day mortality rates associated with high doses of preoperative (+/- intraoperative) RT in patients undergoing curative-intent RPS resection at our institution.

Methods: A total of 99 patients undergoing curative-intent surgery for primary RPS of any histology after preop RT from 2003 – 2021 were identified. All patients received preop RT with or without intraoperative radiotherapy (IORT), followed by macroscopically complete (R0/R1) surgical resection. Patients were excluded if they had multifocal or metastatic disease or if they had surgery or RT at another institution. Clinicopathologic, surgical, radiation, and outcomes data were extracted from our prospectively maintained sarcoma database. Post-operative complications were graded according to the Clavien-Dindo classification system. Univariate and multivariate logistic regression analyses were performed to identify factors associated with postoperative morbidity and mortality.

Results: The clinicopathologic characteristics of the study cohort are summarized in Table 1. Median age was 61 years (range, 25 - 85 years), and 50 (50.5%) patients were female. The most common comorbidities were hypertension and hyperlipidemia. The most common histologic subtypes were dedifferentiated liposarcoma (40%), leiomyosarcoma (26%), and well-differentiated liposarcoma (25%). Most (72%) of the tumors were of intermediate or high grade, and most patients had large tumors, with a median size of 13.5 cm. The median preoperative RT dose was 57.4 Gy, and 17 patients received additional intraoperative RT to a median dose of 10 Gy. Preoperative radiation doses increased over the observation period, from a median dose of 50.4 Gy from 2003 - 2012 to 63 Gy from 2013 - 2021. The median number of organs resected was 2. Postoperative complications within 30 days of surgery occurred in 47% of patients, and severe complications (Clavien-Dindo grades ≥ IIIa) were observed in 20% of patients. The 90-day postoperative mortality rate was 2%. Predictors of severe complications on univariate analysis were en bloc vascular resection (p=0.0002), a higher number of resected organs (p=0.0482), and diabetes as a comorbidity (p=0.0404). Interestingly, the rate of severe complications decreased over the study period, from a rate of 26.3% from 2003-2012 compared to 16.1% from 2013-2021, though this difference was not statistically significant (p=0.3029).

Conclusion: The administration of preoperative +/- intraoperative RT to patients with RPS resulted in similar postoperative complication outcomes as reported after surgery alone, even with RT doses as high as 63 Gy. Continuous advances in surgical and radiotherapeutic expertise resulted in lower complication rates over time despite increasing radiation doses.