title: The effect of body contouring on the dose distribution delivered with volumetric-modulated arc therapy technique.
abstract: The purpose of the study was to investigate the dosimetric effect defining the body structure with various Hounsfield unit (HU) threshold values on the dose distributions of volumetric-modulated arc therapy (VMAT) plans. Twenty patients with prostate cancer and twenty patients with head and neck (H&N) cancer were retrospectively selected. For each patient, the body structure was redefined with HU threshold values of -180 (Body180), -350 (Body350), -700 (Body700), and -980 (Body980). For each patient, dose-volumetric parameters with those body structures were calculated using identical VMAT plans. The differences in dose-volumetric parameters due to the varied HU threshold values were calculated. For the prostate boost target volume, the maximum dose, mean dose, D95%, and D5% with Body180 were higher than those with Body980 by approximately 0.7% (p < 0.001). For H&N target volumes, the changes in D95% of the targets receiving 67.5 Gy, 54 Gy, and 48 Gy between Body180 and Body980 were -1.2%, -0.9%, and -1.2%, respectively (p < 0.001). The differences were larger for H&N VMAT plans than for prostate VMAT plans due to the inclusion of an immobilization device in the irradiated region in H&N cases. To apply all attenuating materials to dose calculation, the body structure would be defined with -980 HU. Otherwise, systematic error of about 1%, resulting in underdosage of the target volume, can occur.
authors.affiliation: Seoul National University Graduate School of Convergence Science and Technology and Seoul National University Hospital. bacillus411@gmail.com.
authors.forename: Jaegi
authors.initials: J
authors.lastname: Lee
authors.forename: Jong Min
authors.initials: JM
authors.lastname: Park
authors.forename: Hong-Gyun
authors.initials: HG
authors.lastname: Wu
authors.forename: Jin Ho
authors.initials: JH
authors.lastname: Kim
authors.forename: Sung-Joon
authors.initials: SJ
authors.lastname: Ye
mesh_terms: D000465:Algorithms; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D006801:Humans; D008297:Male; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D058958:Organs at Risk; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods* / Q000706:statistics & numerical data; D012189:Retrospective Studies