2347 - Stereotactic Body Radiotherapy for the Treatment of Oligometastases Located in the Peritoneum or in the Abdominal Wall: Preliminary Results from a Mono-Institutional Analysis

Purpose/Objective(s): Peritoneal carcinosis can occur in several gastrointestinal or gynecological malignancies and its prognosis is usually poor. With the advent of more effective systemic agents, the overall survival of metastatic patients has been revolutionized and isolated peritoneal or abdominal wall metastases might benefit from local treatments. Traditionally the role of radiotherapy for this challenging scenario was limited to palliative intent with modest results, but Stereotactic Body Radiotherapy (SBRT) might be considered in selected patients with oligometastatic presentation.

Materials/Methods: The present study collects the outcomes of a total of 26 lesions in 20 patients who received SBRT to oligometastatic disease located in the peritoneum or in the abdomino-pelvic wall. Oligometastases were defined according to recent ESTRO/EORTC consensus. Inclusion criteria were as follows: ECOG PS=2, written informed consent, up to 5 lesions to be treated at the same time, patients treated with radiotherapy schedules applying minimum 6 Gy per fraction. Primary endpoint of the study was local control (LC); acute and late toxicity, distant progression-free survival (DPFS), time-to-next systemic treatment (TNST), polymetastatic-free survival (PMFS) and overall survival (OS) were secondary endpoints. Toxicity was assessed according to CTCAE criteria v5.0. Survival estimates were performed using Kaplan-Meier method, uni- and multi-variate analyses were carried out to identify any potentially significant correlation.

Results: Between April 2020 and September 2024 a total of 26 oligometastatic lesions located in the peritoneum or in the abdominal wall detected in 20 patients received SBRT with Helical Tomotherapy. All cases have been assessed in multidisciplinary team. Only in three patients out of 20, more than one lesion received SBRT: 2 lesions in 2 patients, and five lesions in a single case of colorectal cancer with ongoing 3rd line systemic treatment. Median total dose was 30 Gy (27-35 Gy) in 5 fractions (3-5). The most frequent primary neoplasm was ovarian cancer in 14/20, endometrial in 2/20, while the remaining were colorectal, vaginal, pancreatic and non-small cell lung cancer. Four lesions were located in the abdominal wall, while the remaining 22 in the peritoneum. Concurrent systemic therapy was administered in 18/20 patients. With a median follow-up of 15 months (range, 6-59), our 1-year LC was 100%, while 1-year DPFS, PMFS, TNTS and OS rates were 54%, 69%, 61% and 83%, respectively. At statistical analysis, abdominal wall lesions were significantly related to improved OS rates (p=0.03), as well as patients who developed a further oligometastatic progression treated with a second course of SBRT (p=0.04). No G=3 adverse events occurred.

Conclusion: Our preliminary data support the use of SBRT in selected cases of oligometastatic disease located in the peritoneum or in the abdominal wall with excellent results in terms of tolerability and promising clinical outcomes.