title: Impact of pitch angle setup error and setup error correction on dose distribution in volumetric modulated arc therapy for prostate cancer.
abstract: In volumetric modulated arc therapy (VMAT) for prostate cancer, a positional and rotational error correction is performed according to the position and angle of the prostate. The correction often involves body leaning, and there is concern regarding variation in the dose distribution. Our purpose in this study was to evaluate the impact of body pitch rotation on the dose distribution regarding VMAT. Treatment plans were obtained retrospectively from eight patients with prostate cancer. The body in the computed tomography images for the original VMAT plan was shifted to create VMAT plans with virtual pitch angle errors of ±1.5° and ±3°. Dose distributions for the tilted plans were recalculated with use of the same beam arrangement as that used for the original VMAT plan. The mean value of the maximum dose differences in the dose distributions between the original VMAT plan and the tilted plans was 2.98 ± 0.96 %. The value of the homogeneity index for the planning target volume (PTV) had an increasing trend according to the pitch angle error, and the values of the D 95 for the PTV and D 2ml, V 50, V 60, and V 70 for the rectum had decreasing trends (p < 0.05). However, there was no correlation between differences in these indexes and the maximum dose difference. The pitch angle error caused by body leaning had little effect on the dose distribution; in contrast, the pitch angle correction reduced the effects of organ displacement and improved these indexes. Thus, the pitch angle setup error in VMAT for prostate cancer should be corrected.
authors.affiliation: Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, 920-0942, Japan. at@mhs.mp.kanazawa-u.ac.jp.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Takemura
authors.affiliation: Department of Radiology, Seirei Hamamatsu General Hospital, 2-12-12 Sumiyoshi, Naka-ku, Hamamatsu, 430-8558, Japan.
authors.forename: Kumiko
authors.initials: K
authors.lastname: Togawa
authors.affiliation: Department of Radiology, Ishikawa Prefectural Central Hospital, 2-1 Kuratsuki-Higashi, Kanazawa, 920-8530, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Yokoi
authors.affiliation: Department of Radiological Technology, Kanazawa University Hospital, 13-1 Takaramachi, Kanazawa, 920-8641, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Ueda
authors.affiliation: Department of Radiological Technology, Kanazawa University Hospital, 13-1 Takaramachi, Kanazawa, 920-8641, Japan.
authors.forename: Kimiya
authors.initials: K
authors.lastname: Noto
authors.affiliation: Department of Radiological Technology, Kanazawa University Hospital, 13-1 Takaramachi, Kanazawa, 920-8641, Japan.
authors.forename: Hironori
authors.initials: H
authors.lastname: Kojima
authors.affiliation: Department of Radiological Technology, Kanazawa University Hospital, 13-1 Takaramachi, Kanazawa, 920-8641, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Isomura
authors.affiliation: Department of Radiology, Kanazawa University Hospital, 13-1 Takaramachi, Kanazawa, 920-8641, Japan.
authors.forename: Tomoyasu
authors.initials: T
authors.lastname: Kumano
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D061106:Radiotherapy Setup Errors; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies
keywords: Dose distribution; Pitch angle; Prostate cancer; Setup error; Volumetric modulated arc therapy