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Among a large cohort of early stage lung cancer patients, we found that lobectomy had improved survival compared with SBRT, although we found no survival difference between sublobar resection and SBRT. Despite these findings, the potential for unmeasured confounding remains and prospective randomized trials are needed to better compare these treatment modalities.

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curative-intent conventionally fractionated thoracic external-beam radiotherapy (EBRT). Materials/Methods: Using an IRB approved registry of 141 patients treated with definitive intent lung SBRT (BED 100 Gy10) at our institution between 2010 and 2016, we identified 28 patients with a history of conventionally fractionated external-beam radiotherapy to the chest. All patients had a tissue biopsy or PET/CT prior to SBRT. Patients were treated on a linear accelerator-based SBRT system. CTCAEv4 scales were prospectively recorded during follow-ups and utilized for toxicity assessments. Kaplan Meier estimates were utilized for survival analyses. Results: Of the 28 patients included, median age was 71 years (Range [R]:55-84), 60% were female, median ECOG performances status was 1 (R: 0-3). 89.3% of patients received concurrent or sequential chemotherapy with their previous EBRT. 64.3% of lesions were not biopsied prior to SBRT treatment, 10.7% were squamous cell carcinoma, and 25.0% adenocarcinoma histology. The doses ranged from 3400 cGy to 6000 cGy in 1-8 fractions. 12 patients' (42.85%) disease retreated with SBRT was within previous EBRT treatment volume. At median follow up of 13.6 months (R: 4.5 e 62.1), the local in-field control was 92.9% with median time to failure 27.9 months (R: 26.8-29.0). 57.1% of patients progressed (median 7.8 months, R: 1.5-41.3) with first sites including 2 (7.1%) local in-field, 4 (14.3%) lobar out-of-field, 3 (10.7%) new primary, 6 (21.4%) regional, and 7 (25.0%) distant. The 2-year actuarial progression-free survival (PFS) was 25.0% and 2-year actuarial overall survival (OS) was 64.8%. There was minimal toxicity with 1 patient experiencing a grade 3 rib fracture and 2 patients with grade 2 pneumonitis. Conclusion: Our data suggest that lung SBRT is an effective and safe strategy after conventionally fractionated thoracic EBRT, for both in-field and out-of-field local recurrences.

expansions were similar to QACT scans (p-value 0.495 and 0.67, respectively). Conclusion: Our IMPT planning technique demonstrated robustness to variations in rectum size, as evaluated by the doses recalculated on the adjusted volumes and QACT scans. Expansions of +10mm and +15mm best account for naturally occurring variations in rectal volume, and should be examined during plan evaluation.