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

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; Stereotactic Body Radiotherapy (SBRT) might be considered in selected patients with oligometastatic presentation. Oligometastases were defined according to recent ESTRO/EORTC consensus. Inclusion criteria were as follows: ECOG PS ≤ 2, written informed consent, up to five lesions to be treated at the same time, patients treated with radiotherapy schedules applying minimum 6 Gy per fraction. The 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. Statistical associations between clinical variables and outcomes were assessed using Fisher's exact test, and Kruskal-Wallis test, as appropriate. Survival outcomes were estimated using the Kaplan-Meier method and compared using the log-rank test. 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 by a multidisciplinary team. Only in three patients out of twenty did more than one lesion receive SBRT: two lesions in two patients, and five lesions in a single case of colorectal cancer with ongoing third-line systemic treatment. Median total dose was 30 Gy (27-35 Gy) in five 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 twenty-two were located 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. Abdominal wall location and treatment of a subsequent oligometastatic recurrence with a second course of SBRT were both significantly associated with improved OS ( = 0.03 and = 0.04, respectively). No G ≥ 3 adverse events occurred. 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.