Lung Cancer

PV 01 - Poster Viewing Q&A - Session 1

SU_22_3132 - Establishing a Histology-Specific Biologically Effective Dose Threshold for Lung Stereotactic Ablative Radiotherapy (SABR): Is =100 Gy10 Enough?

Sunday, September 15
1:15 PM - 2:30 PM
Location: ASTRO Innovation Hub

Establishing a Histology-Specific Biologically Effective Dose Threshold for Lung Stereotactic Ablative Radiotherapy (SABR): Is ≥100 Gy10 Enough?
S. Abel1, S. Hasan1, V. Verma1, B. Weksler2, A. Colonias1, Z. D. Horne1, and R. E. Wegner1; 1Allegheny Health Network, Department of Radiation Oncology, Pittsburgh, PA, 2Department of Thoracic Surgery, Allegheny Health Network, Pittsburgh, PA

Purpose/Objective(s): Squamous cell carcinoma (SCC) is associated with worse local control and overall survival (OS) compared to adenocarcinoma (ADC) in patients with early stage non-small cell lung cancer (ES-NSCLC) following stereotactic ablative radiotherapy (SABR). Biological effective dose (BED) ≥100 Gy10 improves tumor control, but the differential response between SCC and ADC beyond this threshold is unknown.

Materials/Methods: We queried the National Cancer Database for ES-NSCLC (T1-2N0, Stage I-IIA) patients with SCC or ADC treated with SABR. Receiver operator characteristic (ROC) curve analysis identified an optimal a priori BED threshold for SCC and ADC; outcomes above and below this dose were evaluated separately for SCC and ADC. A sensitivity analysis was performed to further validate the a priori threshold BED. Patterns of BED escalation were assessed using multivariable logistic regression analyses. Association between BED escalation and overall survival was assessed using inverse probability weighted (IPW) propensity-matched multivariable Cox regression models.

Results: Overall, 4,608 patients with SCC and 6,476 patients with ADC (median follow-up: 43 months) were included. The a priori BED threshold for SCC and ADC was 122 Gy10. In the SCC cohort, median tumor size was 2.2 cm (IQR 1.6-3.0 cm) and 44% of cases received BED ≥122 Gy10, with 25% receiving 50Gy/5 Fx (BED=100 Gy10), 18% receiving 48Gy/4 Fx (BED=105.6 Gy10), and 14% receiving 54Gy/3 Fx (BED=151.2 Gy10). In SCC patients, BED ≥122 Gy10 was an independent predictor for longer survival, along with age <75 years, female sex, African American race, lower co-morbidity score, and smaller tumor size on propensity-matched multivariable analysis. Conversely, among ADC patients, BED above or below 122 Gy10 or as a continuous variable did not correlate with survival. The 3 and 5 year IPW propensity-matched Kaplan-Meier survival among SCC receiving BED < 122 Gy10 was 44% and 22% compared to 50% and 26% for BED ≥122 Gy10 (p<0.01, HR:0.84 [0.78-0.90]). Tumors ≤ 3 cm, treatment prior to 2010, and daily SABR were associated with receipt of BED ≥122 Gy10. A subset analysis for tumors ≤3 cm treated with the most commonly employed dose-fractionation schemes in the SCC group demonstrated that median overall survival was significantly longer (p<0.01, HR: 0.80; 95% CI: 0.68-0.95) in the 54 Gy/3 Fx (39.7 months) group compared to the 50 Gy/10 Fx (34.9 months) and 48 Gy/4 Fx (33.6 months) groups.

Conclusion: For ES-NSCLC patients undergoing SABR, BED escalation was an independent predictor of survival in SCC but not ADC, with an optimal value of BED ≥122 Gy10. Thus, histologic-based BED thresholds should be considered in efforts to better individualize SABR management.

Author Disclosure: S. Abel: None. S. Hasan: None. B. Weksler: None. A. Colonias: President; Internal Review Board at Allegheny Health Network. R.E. Wegner: None.

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