Interstitial High-Dose-Rate Brachytherapy Combined with External Beam Radiation Therapy for Dose Escalation in the Primary Treatment of Locally Advanced, Non-Resectable Superior Sulcus (Pancoast) Tumors: Results of a Monocentric Retrospective Study

<b>Objectives</b>: To analyze the results of interstitial (IRT) high-dose-rate (HDR) brachytherapy (BT) in the primary treatment of patients with unresectable superior sulcus tumors (SST) combined with external beam radiotherapy (EBRT). <b>Methods</b>: Between 2013 and 2023, seven patients with unresectable SST were treated with combined BT and EBRT with or without concomitant chemotherapy. The patients' median age was 64 years (range, 49-79 years) and median tumor volume was 146.8 cm³ (range, 29.3-242.3 cm³). A median BT dose of 8 Gray (Gy) (range, 5-10 Gy) was prescribed and delivered in a single fraction. A median EBRT dose of 54 Gy (range, 30-59 Gy) was prescribed and administered normofractionated (single dose: 1.8 Gy). <b>Results</b>: We report the results of seven patients with SST treated with combined BT and EBRT and followed for a median of 38 months. The overall clinical response rate was 83.33% with five out of six patients achieving local control, while one out of six (16.66%) showed local and general progression. No deaths were attributed to the treatment itself; rather, one patient died during the course of therapy as a result of systemic progression. The most common radiation-related adverse events were grade I-II fatigue and mild paresthesia. No severe toxicity (CTCAE ≥ III°) was observed with interstitial high-dose-rate (HDR) BT combined with EBRT. <b>Conclusions:</b> For patients with unresectable superior sulcus tumors, interstitial HDR BT in combination with EBRT is a feasible treatment option that offers the potential for local control and long-term survival. The findings of this study should be validated in a larger patient cohort.