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Abstract
Objectives In conformal radiotherapy planning for lung cancer, respiratory movements are not taken into account when a single computed tomography (CT) scan is performed. This study examines tumor movements to design individualized margins to account for these movements and evaluates their dosimetric impacts on planning volume and organs at risk. Design Prospective self-controlled dosimetric study of radiotherapy treatment planning for NSCLC patients presenting to the National Cancer Institute, Cairo University from March 2016 to April 2017. Methods 30 patients were enrolled in the study. Each patient was simulated using CT simulator and instructed to breathe normally, at full maximum inspiration and at full maximum expiration to create 2 RT plans; a reference plan and respiratory correlated plan. Target volumes in cubic centimeter along with doses to organs at risk were obtained. Comparisons of volumetric and dosimetric parameters were performed using paired Student t-tests. Results The respiratory correlated plan is better than the old conventional one. There was marked reduction in PTV in all cases; Mean±SD (325.4±296.23 cc vs. 498.2±263.2 cc, p <0.001). Lung dosimetric parameters were reduced significantly; MLD (7.3±2.65 vs. 9±2.8 Gy, p = 0.04), V20 (11.6±4.9 vs. 14±5.5 %, p <0.001), V30 (8.4±3.8 vs. 10±4 %, p <0.001) and V5 (31.63±11.32 vs. 38.6±12%, p = 0.05). For heart, MD (8.27±13.5 vs. 11.24±11 Gy, p = 0.03), whereas V30 was not significantly changed.Concerning esophagus, MD (11.3±6.93 vs. 15.3±8 Gy, p = 0.03) and the V50 (7±11.3 vs. 12±14.2 %, p <0.001). Also there was significant decrease in maximum dose reaching spinal cord (20.8±13 vs. 27.9±14Gy, p <0.001). Conclusion Using a system of CT scans at inhale, exhale, and free breathing phases of respiration allows an excellent opportunity to quantify the extent of respiratory motion and tumor deformation in NSCLC. Smaller and more conformal planning volume was obtained compared to the reference technique. This produced a small but consistent advantage to spare the lung for a similar coverage. In addition, respiratory correlated treatment plans can significantly reduce excessive radiation doses to the surrounding organs at risk, reducing acute & long-term radiation induced toxicities. We recommend the use of our technique in cases of NSCLC as a simple method - especially in departments where 4D CT is not available - for improving the definition of internal target volume and tumor targeting