Page 33 - Organ motion in children for high-precision radiotherapy - Sophie Huijskens

2.3 | Results
The mean interfractional motion of the kidneys was smaller than 1.5 mm in our study population (Table 2.2). Figure 2.1 shows absolute median interfractional organ motion in children. The highest median values and largest spreads in interfractional motion in both kidneys were found in the CC direction (Figure 2.2), smaller spreads were found in the LR and AP directions. Interfractional renal motion varied largely between patients (Figure 2.2). In all directions and organs, multiple patients’ (2-5) variance differed significantly (p < 0.01) from the mean group variance.
Linear regression analysis
Since age and height were highly correlated (R2 > 0.9, graphs not shown) and kidney motion was largest in CC direction, we analyzed only height in relation to organ motion in CC direction. Linear regression analysis did not show a correlation between random errors of renal and diaphragmatic motion in the CC direction and height (Figure 2.3). Significant (p < 0.05), but weak correlations were found between interfractional kidney motion and diaphragmatic motion, except for the LR direction in the right kidney (Figure 2.4). The systematic and random errors in the two subgroups, based on median height, differed less than 1.5 mm.
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