Tumor Regression and Positional Changes in Non-small Cell Lung Cancer During Radical Radiotherapy

Introduction: We have used respiratory-correlated cone beam computed tomography (rcCBCT) imaging to study the volumetric and positional changes that occur throughout the course of radical radiotherapy in non-small cell lung cancer (NSCLC). Methods: Tumor volumes and centers of mass were recorded and analyzed on weekly serial rcCBCT images of NSCLC patients treated with radical radiotherapy to a dose ≥45 Gy with concurrent chemotherapy. Results: Sixty patients with locally advanced NSCLC were included; in 31 patients, the primary tumor was peripheral and thus suitable for contouring. There was a mean percent decrease of 40.2% by fraction 15 and 51.1% by treatment completion. Among all 60 patients, 19 patients (32%) had more than 30% regression by fraction 15 and 25 patients (81%) by treatment completion. Statistically significant tumor migration in at least one direction between the first and the last 2 weeks was demonstrated in 14 of 27 patients. Clinically relevant changes (atelectasis and effusions) were noted in 11 of 29 visually assessed patients. Conclusions: Current rcCBCT image quality allows assessment of tumors located more peripherally. Significant tumor regression was documented in the majority of patients. In view of these observations, the suitability of adaptive radiotherapy in radical lung cancer treatment should be further investigated.