title: Uncertainty in patient set-up margin analysis in radiation therapy.
abstract: We investigated the uncertainty in patient set-up margin analysis with a small dataset consisting of a limited number of clinical cases over a short time period, and propose a method for determining the optimum set-up margin. Patient set-up errors from 555 registration images of 15 patients with prostate cancer were tested for normality using a quantile-quantile (Q-Q) plot and a Kolmogorov-Smirnov test with the hypothesis that the data were not normally distributed. The ranges of set-up errors include the set-up errors within the 95% interval of the entire patient data histogram, and their equivalent normal distributions were compared. The patient set-up error was not normally distributed. When the patient set-up error distribution was assumed to have a normal distribution, an underestimate of the actual set-up error occurred in some patients but an overestimate occurred in others. When using a limited dataset for patient set-up errors, which consists of only a small number of the cases over a short period of time in a clinical practice, the 2.5% and 97.5% intervals of the actual patient data histogram from the percentile method should be used for estimating the set-up margin. Since set-up error data is usually not normally distributed, these intervals should provide a more accurate estimate of set-up margin. In this way, the uncertainty in patient set-up margin analysis in radiation therapy can be reduced.
authors: Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, S1 W6 Chuo-ku, Sapporo, Japan.
authors: Junji
authors: J
authors: Suzuki
authors: Kunihiko
authors: K
authors: Tateoka
authors: Katsumi
authors: K
authors: Shima
authors: Yuji
authors: Y
authors: Yaegashi
authors: Kazunori
authors: K
authors: Fujimoto
authors: Yuichi
authors: Y
authors: Saitoh
authors: Akihiro
authors: A
authors: Nakata
authors: Tadanori
authors: T
authors: Abe
authors: Takuya
authors: T
authors: Nakazawa
authors: Kouichi
authors: K
authors: Sakata
authors: Masato
authors: M
authors: Hareyama
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D006801:Humans; D008297:Male; D016011:Normal Distribution; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D018787:Radiation Oncology / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods; D035501:Uncertainty; D014965:X-Rays