Page 47 - Organ motion in children for high-precision radiotherapy - Sophie Huijskens

3.3 | Results Patient population
The mean ages (range) of children and adults were 10.3 (3.1–17.8) and 59.9 (34.1–94.0) years, respectively (Table 3.1). Mean heights (range) in children and adults were 140 cm (92–184 cm) and 175 cm (160–203 cm), respectively. Thirty-three of 35 children and all adults were treated in supine head-first position. Anesthesia was required in five children (mean age 5.2 (range, 3.1–7.6) years; Figure 3.3); seven children of similar ages (mean 5.8 (range 3.3–7.9) years) were treated without anesthesia. Overall, 850 CBCT images were successfully registered (range 5–30 per patient). In some patients one or both kidneys and the diaphragm could not be registered due to various reasons (see Appendix 3).
Organ position variation
The upper panel of Figure 3.1 shows the distributions of the individual means and the group means in children and adults for all organs in all directions. The one-sample t-test showed that the group means (Table 3.2) were not significantly different from the reference value 0 (adjusted p>.007), meaning that the systematic set-up error for patient positioning was minimal. The lower panel of Figure 3.1 shows the distributions of the individual SDs in the two patient groups. In both groups, renal position variation was largest in the CC direction. The median 3D vector lengths of the right and left kidney were significantly smaller in children as compared to those in adults (Figure 3.2: 2.8, 2.9 mm vs. 5.6, 5.2 mm, respectively; p<.05).
Table 3.2 presents the values of Σ and σ. For children, Σ values were significantly smaller in the CC direction of the right kidney, the CC and AP directions of the left kidney, and the CC direction of the diaphragm when compared to adults (adjusted p<.007). Pediatric σ values were significantly smaller than those for adults for all directions of the right kidney, and the CC and AP directions of the left kidney (adjusted p<.007). Organ position variation in the five children treated with anesthesia was not significantly different compared to seven children of similar age ranges (3.1–7.6 and 3.3–7.9 years, respectively) who had no anesthesia (adjusted p>.007).
Correlation between organ position variation and patient height and BMI
Correlations between interfractional organ position variation and height were negligible, taking all patients into account (Figure 3.3). Spearman’s ρ varied from 0.277 (correlation between the CC right kidney position variation and height) to 0.393 (correlation between AP right kidney position variation and height). Spearman’s ρ for the pediatric and adult patients separately indicated only negligible, non- significant correlations (Supplementary Figure 3.1(A,B)). Likewise, correlations between interfractional organ position variation and height in the subgroup of children and adults with overlapping heights were negligible and non-significant (Supplementary Figure 3.2). Finally, correlations with BMI were also found to be negligible, though significant (Supplementary Figure 3.3).
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