Effective Adaptive Radiotherapy for Locally Advanced Lung Cancer Treated with 3D Conformal Technique

Background: The reduction in tumor volume during the treatment of locally advanced non-small cell lung cancer (NSCLC)with chemoradiotherapy allows the application of adaptive radiotherapy strategy. Adaptive planning has the potential forimproving radiotherapy planning indices and dose escalation while respecting the dose to the organs at risk (OARs).Aim: To evaluate the benefit of adaptive radiotherapy in patients with advanced NSCLC treated with conformal technique.Methods: In this dosimetric planning study, we included computerized tomography data-sets from 10 patients with locallyadvanced NSCLC who responded to the first 22 fractions (44 Gy) and achieved ˃ 20% regression in gross tumor volume. We designed for each patient two plans. Plan 1 (conventional planning) in which the whole prescribed dose (64 Gy) was delivered to the planning target volume 1 (PTV1). Plan 2 (adaptive planning) was divided into plan 2A delivering 44 Gy to PTV1 and plan 2B delivering 20 Gy to PTV2. In plan 2B we re-delineated the PTV and all the target volumes on the repeated CT images to deliver the rest of the prescribed dose (20 Gy). Plan 2A and Plan 2B were summed to measure the accumulated dose delivered to OARs.Results: The mean PTV2 was significantly smaller than the mean PTV1 (p < 0.001) with 53% reduction. Adaptive planningresulted in 13.2% mean reduction in the maximum dose to the spinal cord (p < 0.001), 10.4% in esophagus V35 (p < 0.001), 11.4% in esophagus V50 (p < 0.001), 24.3% in mean lung dose (p=0.001) and 19.7% in lung V20 (p < 0.001). The reduction in heart d-max and heart mean dose was not significant.Conclusion: The adaptive radiotherapy technique used in our study can reduce the irradiated volume and minimize the dose delivered to OARs. This simple applicable technique can be easily implemented in limited resources centers.