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Abstract IA16: A prospective trial of SBRT boost for stage III non-small cell lung cancer

Purpose/Objective: Escalation of radiation dose in stage III lung cancer has been problematic and no prospective studies have confirmed a survival benefit for patients receiving >60Gy concurrent with chemotherapy. Nonetheless, conventional treatment approaches may not deliver adequate doses to the primary tumor. We report on the feasibility of using SBRT as a means of dose escalation of the primary tumor mass for patients found to have resolution of mediastinal nodal disease following conventional chemoradiotherapy (CRT). The goal was to deliver a biological effective dose (BED) of more than 100 Gy to the primary tumor mass (CRT + SBRT boost doses combined). Methods: Patients with biopsy proven stage II/III NSCLC underwent CT or PET-CT scanning one month following completion of conventional CRT (59.4 Gy or greater). Eligible patients were required to have achieved either negative or only minor FDG residual uptake in nodal disease within the mediastinum. Patients with PET positive residual disease (≤7 cm) within the site of the primary tumor were included. Tumor volumes were defined using 3d planning based on the location of the initial tumor and PET uptake. The prescription dose was 10 Gy per fraction X 2 (20 Gy total dose, BED10 =112Gy combined CRT and SBRT boost dose) and later patients with tumors touching the mediastinum as per RTOG definition received SBRT to the residual tumor of 650cGy X 3 (1950 total dose). Patients underwent routine follow-up with repeat CT scans every 3 months or PET/CT as indicated. The primary endpoints were toxicity and tumor response. Target enrollment is 37. Results: 35 patients (33 reviewed here) have been enrolled with a median age 63. Stages included were IIB (n=4), IIIA (n=18), and IIIB (n=13). Additionally, 9 patients were screened by 1 month post-CRT PET/CT and found to be not eligible: 2 patients with a CR after initial therapy and 7 with significant residual uptake in the mediastinum or metastatic disease. Pathologies included squamous cell carcinoma (75%), adenocarcinoma (11%), large cell carcinoma (10%) and lung cancer NOS (4%). Median combined BED was 110 Gy (range 110–120). Mean PTV volume was 51.3 cm3 (range 46–2571cc) and average treatment coverage to 20 Gy prescription dose was 96.8%. Grade <3 toxicities have been very low. Only 4 local failures have occurred. Of these, two presented approximately 12 months after treatment with grade 5 toxicity, both of whom had large cavitary recurrences of their malignancies which involved the hilum. One patient had an SBRT boost volume encompassing the hilum, the other did not, but both anecdotally died of pulmonary hemorrhage. Of the 33 patients reported here, 16 patients had “medial” tumors of which 10 received 1000cGy X 2 boosts to the hilum. As a safety precaution, for patients with tumor volumes touching the hilum, a revised SBRT dose of 650cGy X 3 (1950cGy total boost, BED10 =102Gy) was delivered. Thus far, 6 patients received 650cGy X 3 boost that included the hilum in most cases. No toxicities have been noted in these patients. Conclusions: The use of linac-based SBRT boost as a means of dose escalation for limited residual NSCLC following definitive chemoradiotherapy is a feasible treatment approach with minimal toxicity.