Quantification of Tumor Volume Changes During Radiotherapy for Non–Small-Cell Lung Cancer

Purpose Dose escalation for lung cancer is limited by normal tissue toxicity. We evaluated sequential computed tomography (CT) scans to assess the possibility of adaptively reducing treatment volumes by quantifying the tumor volume reduction occurring during a course of radiotherapy (RT). Methods and Materials A total of 22 patients underwent RT for Stage I-III non–small-cell lung cancer with conventional fractionation; 15 received concurrent chemotherapy. Two repeat CT scans were performed at a nominal dose of 30 Gy and 50 Gy. Respiration-correlated four-dimensional CT scans were used for evaluation of respiratory effects in 17 patients. The gross tumor volume (GTV) was delineated on simulation and all individual phases of the repeat CT scans. Parenchymal tumor was evaluated unless the nodal volume was larger or was the primary. Subsequent image sets were spatially co-registered with the simulation data for evaluation. Results The median GTV reduction was 24.7% (range, −0.3% to 61.7%; p < 0.001, two-tailed t test) at the first repeat scan and 44.3% (range, 0.2–81.6%, p < 0.001) at the second repeat scan. The volume reduction was not significantly different between patients receiving chemoradiotherapy vs. RT alone, a GTV >100 cm3 vs.