P05.02 Does Non-Small Cell Lung Cancer Histologic Type Influence Outcomes with Single-Fraction Stereotactic Body Radiotherapy?

Abstract

For early stage medically inoperable Non-Small Cell Lung Cancer (NSCLC) treated with fractionated stereotactic body radiotherapy (SBRT), when compared by biologically equivalent dose (BED) higher rates of local failure have been associated with squamous (SqC) histology compared to adenocarcinoma (AC) for equivalent BEDs. We sought to determine if histology outcomes differed when using single-fraction schedules (SF-SBRT). An IRB-approved prospective lung SBRT data registry was surveyed from 12/2009 till 12/2019 for all patients (pts) receiving SF-SBRT with minimum 6-month follow up with biopsy-proven AC or SqC excluding bronchoalveolar and “NSCLC not-otherwise specified” cases. Doses employed were either 34 Gy, planned per RTOG 0915, or 30 Gy, planned per RPCI-124407. Outcomes of interest included cumulative incidence rates of local (LF), nodal (NF), and distant (DF) failure and overall survival (OS), as well as treatment-related toxicity graded per CTCAE version 3.0. 229 SF-SBRT pts treated over 10 years had a 2-year LF rate of 7.28%. For this analysis 113 (49.3%) met study’s pathology criteria and had a 2-year LF rate of 8.41%. No association was seen between histology type and the SF-SBRT dose given: 65 pts (57.5%) had AC, of these 19 (29.2%) and 46 (70.8%) received 30 Gy and 34 Gy, respectively. Of 48 SqC pts (42.5%), 17 (35.4%) and 31 (64.6%) received 30 Gy and 34 Gy, respectively. Median follow up was 22.9 months. Patient characteristics were balanced between histologies. Median tumor size was 1.9 cm and 2.05 cm for AC and SqC, respectively. When comparing tumor features for each histology or by dose group, there were no significant (NS) differences including specifically tumor distance from the chest wall. Comparing total Ac vs. SqC cohorts, 2-year LF rates in % were 7.32 vs. 9.64, respectively (p=0.9805). In %, 2-year LF, NF, DF and OS rates for AC for 30 Gy and 34 Gy, respectively, were 10.84 vs. 6.41; 10.53 vs. 16.24; 15.79 vs. 13.04; 77.9 vs.71.2 (all NS). In %, 2-year LF, NF, DF, and OS rates for SqC for 30 Gy and 34 Gy, respectively, were 11.76 vs. 8.08; 5.88 vs. 17.94; 23.53 vs. 9.68; 70.6 vs. 77.1 (all NS). There were no grade 4/5 toxicities and NS differences in any other toxicity rate by histology or dose. For AC pts, pneumonitis rates were: 4 pts (6.2%) with grades 1-2; chest wall toxicity rates were: 7pts (10.8%) with grade 1-2 and 1 (1.5%) with grade 3. For SqC, pneumonitis rates were: 4 pts (8.3%) with grade 1-2 rates pneumonitis; chest wall toxicity rates were: 10 (20.8%) with grade 1-2 only. SqC LF rates are similar to AC’s with either SF-SBRT schedule and no significant differences were seen for other outcomes or for toxicity profiles by histology and dose. This suggests equivalent efficacy for SF-SBRT doses independent of NSCLC histology