(S024) Correlation of Survival to CBCT-Based Tumor Response During Chemoradiation in Patients With Stage III Non–Small-Cell Lung Cancer

Salma Jabbour, MD; Rutgers Cancer Institute of New Jersey

Purpose and Objectives: Stage III non–small-cell lung cancer (NSCLC) treated with chemoradiotherapy (CRT) results in a median survival of 15–18 months. We evaluated the correlation between patient survival and reduction in gross tumor volume (GTV) using weekly cone-beam computed tomography (CBCT) to assess whether this could be prognostic of survival. We hypothesized that a greater percent decline in primary lung tumor volume during the course of treatment would correlate to improved patient survival.

Materials and Methods: Patients with stage III NSCLC who received CRT between July 2009 and September 2012 and had daily CBCTs performed as part of their RT course were included in this institutional review board-approved study. Primary GTVs were contoured from CBCT images obtained on Days 1, 8, 15, 22, 29, 36, and 42. Percentage changes in GTV per patient were determined by calculating [(GTV Day 1 – GTV Day 42)/(GTV Day 1)]. MATLAB and Excel 2010 were used to perform t-test analysis of the data, and Kaplan-Meier survival curves were generated based on median GTV reduction with censored patient data. Associations with GTV reduction and time to death were evaluated with a Cox proportional hazards model. 

Results: Thirty-seven patients (median age 67.1 years; standard deviation [SD] = 8.8 years) met the criteria for inclusion in this study from December 2009 to May 2013. Median follow-up was 8.2 months (range: 3–32.9 mo). Median GTV reduction was observed to be 39.2% (range: 0%–79.7%) from Day 1 to Day 42 of radiotherapy. For every 10% decrease in GTV size, the risk of death was lowered by 38.6% (P = .0009). Local recurrence occurred in 29.7% of patients, and distant recurrence occurred in 72.2%. For every 10% reduction in GTV, the risk of local recurrence and distant metastases was lowered by 29.2% (P = .0095) and 26.2% (P = .027), respectively. 

Conclusions: Reductions in primary GTV volume, as determined by weekly CBCT, appear to correlate to patient survival, local recurrence, and distant metastases. Further study with additional patients and longer follow-up is necessary. Such findings may help to determine which patients may also benefit from adaptive planning.

Proceedings of the 96th Annual Meeting of the American Radium Society - americanradiumsociety.org