Lung Cancer

PV 01 - Poster Viewing Q&A - Session 1

SU_34_3255 - Quantitative Volumetric Disease Burden Response to Predict Benefit of Consolidative Thoracic Radiotherapy in Extensive Stage Small Cell Lung Cancer (ES-SCLC)

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

Quantitative Volumetric Disease Burden Response to Predict Benefit of Consolidative Thoracic Radiotherapy in Extensive Stage Small Cell Lung Cancer (ES-SCLC)
J. L. Anderson1, C. E. Anderson2, M. C. Xu1, and E. C. Osmundson3; 1Vanderbilt University School of Medicine, Nashville, TN, 2Gillings School of Global Public Health, University of North Carolina, Chapel Hill, NC, 3Department of Radiation Oncology, Vanderbilt University Medical Center, Nashville, TN

Purpose/Objective(s): The role of radiotherapy (RT) in ES-SCLC remains unclear. Consolidative thoracic radiotherapy (CTRT) after chemotherapy (chemo) confers a survival benefit in select studies, however identifying predictors of response among heterogenous ES-SCLC presentations has been elusive. Prior studies evaluating CTRT mandated prophylactic cranial irradiation (PCI), which may no longer be standard of care. Data clarifying which ES-SCLC patients (pts) benefit from local radiotherapy (CTRT and/or PCI) are needed. We hypothesized that quantitative volumetric imaging of disease burden and therapy response, in conjunction with clinical factors, will allow for more rational approaches to local therapy selection in ES-SCLC.

Materials/Methods: We retrospectively identified 56 pts with ES-SCLC with a partial or complete chemo response and were treated with CTRT. Pre-chemo and post-chemo CT scans were contoured for volume of intrathoracic disease. Univariate (UVA) and multivariate (MVA) cox proportional hazards regression models tested for associations between clinical predictors, volumetric disease changes (Results: Median OS was 9.8 mos (range 3.8-54.2) with a median follow up time of 13.6 mos. 38 pts received CTRT. On UVA analysis, receipt of CTRT was associated with PFS (HR 0.44, CI 0.24- 0.82; p=.009), OS (HR 0.46, CI 0.24-0.88, 0.0187), and TIF (HR 0.24, CI 0.12-0.48, p<0.001) as was presence of >6 ET-mets (PFS [HR 2.64, CI 1.45-4.81, p=.0015]; OS [HR 2.99, CI 1.57-5.67, p<0.001], TIF [HR 4.06, 95%, CI 2.14-7.70; p<.001]), while % decrease in intrathoracic disease volume, initial intrathoracic disease volume, and receipt of PCI were not (all p≥0.095). Intrathoracic progression as first site of failure was negatively associated with receipt of CTRT (HR 0.15, 95%, CI 0.03-0.77; p=.022) and sex (female vs. male HR 0.26, CI 0.08-0.85). On MVA analysis, when adjusting for sex, age, >6 ET-mets, and PCI, receipt of CTRT remained protective against intrathoracic progression as first site of failure (HR 0.15, CI 0.02-0.99; p=.0486) and improved time to intrathoracic failure (HR 0.35, 95%, CI 0.17-0.774; p=.006).

Conclusion: Initial intrathoracic disease volume, post-chemo intrathoracic disease volume reduction, and PCI were not significantly associated with PFS, OS, or TIF in our population. Receipt of CTRT was significantly associated with longer TIF and a decreased rate of intrathoracic progression as first site of failure. Improved intrathoracic control with CTRT may be more impactful in pts with reduced extrathoracic disease burden. Future studies evaluating CTRT in ES-SCLC pts treated with immunotherapy-containing regimens are needed.

Author Disclosure: J.L. Anderson: None. M.C. Xu: None. E.C. Osmundson: None.

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