Page 45 - Organ motion in children for high-precision radiotherapy - Sophie Huijskens

estimated [6]. To investigate the systematic set-up error for patient positioning, we used the one- sample t-test to test whether group means significantly differed from 0 (i.e., reference value of organ position in the refCT).
Since not all data fitted the normal distribution (tested with the Shapiro–Wilk’s test for normality), the non-parametric Levene’s test for equality of variance was used to analyze the difference of Σ. To test for the difference of σ, the Mann–Whitney U-test was used. This test was also used to investigate possible differences in organ position variation in children of similar ages treated with and without anesthesia. Since a mutual dependency between renal and diaphragmatic position variation can be assumed, and seven directions were tested (i.e., CC, LR, AP in both kidneys and CC only in the diaphragm), we adjusted p values using the Bonferroni correction to reduce the chance of finding significant differences by coincidence [20]. Differences were considered to be significant if test outcomes showed a p value<.007 (i.e., 0.05/7).
To investigate the possible correlation between renal and diaphragmatic position variation and patient height, Spearman’s rank correlation coefficients (ρ) were calculated for the whole cohort, for pediatric and adult patients separately, and for the children and adults with overlapping heights (significance level p<.05). Additionally, the correlation with BMI (weight (kg)/(height (m))2) was investigated. We did not include age in our analyses, since children and adults physically differ; adolescents can be taller than small adults.
Data were analyzed using statistical software SPSS version 22.0 for Windows (SPSS, INC, Chicago, IL, USA) and the R software package version 3.2.1 (R Foundation for Statistical Computing, Vienna, Austria).
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