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.
Written by:
Suzuki J, Tateoka K, Shima K, Yaegashi Y, Fujimoto K, Saitoh Y, Nakata A, Abe T, Nakazawa T, Sakata K, Hareyama M. Are you the author?
Department of Radiation Oncology and Medical Physics, Graduate School of Medicine, Sapporo Medical University, S1 W6 Chuo-ku, Sapporo, 060-8556, Japan.
Reference: J Radiat Res. 2012 Jul 1;53(4):615-9.
doi: 10.1093/jrr/rrs003
PubMed Abstract
PMID: 22843628
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