2438 - Outcomes and Toxicity of 60 Gy in 8 Fractions Stereotactic Body Radiotherapy to Peripheral Tumors Adjacent to the Chest Wall: A Single Institution Experience

Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) is a well-established treatment for peripheral lung tumors; however, its use for tumors near or abutting the chest wall raises concerns regarding toxicity. We report our institution’s experience in treating these tumors with SBRT using a regimen of 60 Gy in 8 fractions. We hypothesize that this fractionation scheme, with a biologically effective dose (BED) > 100 Gy, results in high local control with favorable chest wall toxicity

Materials/Methods: This retrospective study analyzed 80 patients with a total of 98 lesions diagnosed with either primary (n=61) or metastatic (n=19) peripheral lung tumors between 2019 - 2024, all treated with SBRT at 60 Gy in 8 fractions. Tumors adjacent to the chest wall were defined as those with planning tumor volumes (PTVs) within 1 cm of the chest wall. 82 out of 98 lesions (83.67%) were directly abutting the chest wall. Data on chest pain were available for 45 out of 80 patients, while rib fracture assessment was conducted in 77 patients. The incidence of pneumonia was also documented. The primary endpoints were local control and chest wall toxicity, including chest wall pain (graded per CTCAE v5) and rib fractures. Secondary endpoints were median overall survival (OS) and median progression-free survival (PFS). OS and PFS outcomes were evaluated using the Kaplan-Meier method.

Results: Lung tumor size ranged from 7 to 60 mm (mean 23.28 mm). At a median follow-up of 24.85 months, local control was achieved in 97.5% of tumors. In subgroup analysis, PFS for primary lung cancer patients was 79.63 months (95% CI : 58.16-101.11). The median OS for primary lung cancer patients was 63.90 months (95% CI: 32.55–95.25) with 3-and 5-year OS of 70.67% and 56%, respectively. Among the 45 patients with available chest pain data, 2 (4.4%) experienced chest pain, both reported as grade 3. Rib fractures were identified in 5 of 77 patients (6.5%). Additionally, 14 patients developed pneumonia, with 2 cases confirmed as radiation-induced pneumonitis.

Conclusion: SBRT with 60 Gy in 8 fractions for peripheral lung tumors adjacent to the chest wall demonstrated excellent local control rates (97.5%) with minimal toxicity. Chest wall pain was infrequent (4.4%), while rib fractures occurred in only 6.5% of patients. These results suggest that this fractionation schedule provides high tumor control with low toxicity, making it a viable option for peripheral lung tumors near or abutting the chest wall. Prospective studies are warranted to confirm these findings.