Importance of Radiotherapy Timing and Resection Margin Status for Postoperative Radiotherapy in Extremity STS

Abstract

Purpose/Objective(s): We evaluated outcomes of palliative proton quadshot and stereotactic proton therapy to unresectable disease for patients with recurrent/metastatic sarcoma. Materials/Methods: From 2014 to 2018, 27 patients with recurrent or metastatic sarcomas were treated to 39 total sites with palliative proton RT with quad shot (14.8Gy/4 twice daily) or SBRT (27Gy/3 or 30Gy/ 5). Treatment for spine or brain metastases were not included. Follow up interval was defined as from the beginning of proton therapy. Analyzed factors included concurrent systemic therapy, Karnosfky performance status (KPS), initial treatment, presenting symptoms, and total radiation dose. Outcomes of interest included toxicity, ability to receive further systemic therapy, subjective palliative response and objective response using the RECIST criteria (stable, progressive, partial or complete response) as determined by two independent radiation oncologists. Results: Of the 39 total sites, 3 (7%) received SBRT and 36 (92%) received quad-shot with proton therapy. Of the 36 who received quadshot, 23 (64%) received 3 rounds. Median follow up was 8 months (IQR 4-13) for the entire cohort and 10 months (IQR 7-21) for living patients. Survival at 6 months was 70% and at 1 year was 52%. Median KPS was 90% at the time of first treatment. 89% (nZ24) of patients had soft tissue sarcomas with the most common histology being gastrointestinal stromal tumor (nZ7) while the remaining 3 patients had sarcomas arising from the bone. 25 (64%) sites were located in the abdomen or pelvis. 26 (67%) sites had been previously resected prior to recurrence and 5 (13%) sites had received prior RT. 17 (44%) treatments involved concurrent systemic therapy and 10 (37%) patients received further systemic therapy following proton therapy. Of the 17 sites treated with concurrent systemic therapy, 6 received chemotherapy, 10 received targeted therapy and 1 received both. Overall subjective palliative response was 77%. The most common presenting symptom was pain (87%, nZ34), which improved in 76% (nZ26) of cases. Of the 34 patients who had post-treatment imaging, overall objective response showing at least no change in size of the treated site was 79% (nZ27) with decrease in size of lesions observed in 26% (nZ9) of cases. 4 grade-3 acute toxicities were observed including abdominal infection, diarrhea, colonic obstruction and esophageal ulcer. None of these patients received concurrent systemic therapy. Conclusion: The proton quad-shot regimen and SBRT demonstrate favorable palliative response and toxicity profile. Even in the setting of gross disease, 37% of patients went on to receive further systemic therapy. This serves as a feasible alternative for patients with previously treated, recurrent or metastatic sarcomas where overall treatment options may be limited.