title: Intermediate Megavoltage Photon Beams for Improved Lung Cancer Treatments.
abstract: The goal of this study is to evaluate the effects of intermediate megavoltage (3-MV) photon beams on SBRT lung cancer treatments. To start with, a 3-MV virtual beam was commissioned on a commercial treatment planning system based on Monte Carlo simulations. Three optimized plans (6-MV, 3-MV and dual energy of 3- and 6-MV) were generated for 31 lung cancer patients with identical beam configuration and optimization constraints for each patient. Dosimetric metrics were evaluated and compared among the three plans. Overall, planned dose conformity was comparable among three plans for all 31 patients. For 21 thin patients with average short effective path length (< 10 cm), the 3-MV plans showed better target coverage and homogeneity with dose spillage index R50% = 4.68±0.83 and homogeneity index = 1.26±0.06, as compared to 4.95±1.01 and 1.31±0.08 in the 6-MV plans (p < 0.001). Correspondingly, the average/maximum reductions of lung volumes receiving 20 Gy (V20Gy), 5 Gy (V5Gy), and mean lung dose (MLD) were 7%/20%, 9%/30% and 5%/10%, respectively in the 3-MV plans (p < 0.05). The doses to 5% volumes of the cord, esophagus, trachea and heart were reduced by 9.0%, 10.6%, 11.4% and 7.4%, respectively (p < 0.05). For 10 thick patients, dual energy plans can bring dosimetric benefits with comparable target coverage, integral dose and reduced dose to the critical structures, as compared to the 6-MV plans. In conclusion, our study indicated that 3-MV photon beams have potential dosimetric benefits in treating lung tumors in terms of improved tumor coverage and reduced doses to the adjacent critical structures, in comparison to 6-MV photon beams. Intermediate megavoltage photon beams (< 6-MV) may be considered and added into current treatment approaches to reduce the adjacent normal tissue doses while maintaining sufficient tumor dose coverage in lung cancer radiotherapy.
authors.affiliation: Department of Biomedical Engineering, Tianjin University, Tianjin, China.|Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut, United States of America.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Biomedical Engineering, Tianjin University, Tianjin, China.
authors.forename: Yuanming
authors.initials: Y
authors.lastname: Feng
authors.affiliation: Department of Radiation Oncology, William W. Backus Hospital, Norwich, Connecticut, United States of America.
authors.forename: Munir
authors.initials: M
authors.lastname: Ahmad
authors.affiliation: Department of Biomedical Engineering, Tianjin University, Tianjin, China.|Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut, United States of America.
authors.forename: Xin
authors.initials: X
authors.lastname: Ming
authors.affiliation: Center for Radiation Physics and Technology, West China Hospital Cancer Center, Sichuan University, Chengdu, China.
authors.forename: Li
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut, United States of America.
authors.forename: Jun
authors.initials: J
authors.lastname: Deng
mesh_terms: D000465:Algorithms; D019583:Dose Fractionation, Radiation; D004947:Esophagus / Q000528:radiation effects; D006321:Heart / Q000528:radiation effects; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D061766:Proton Therapy / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D013116:Spinal Cord / Q000528:radiation effects; D014132:Trachea / Q000528:radiation effects