Page 69 - Organ motion in children for high-precision radiotherapy - Sophie Huijskens

4.3 | Results
Mean organ position variation was smaller than 1.0 mm (range: -6.9 to 7.4 mm) for the abdominal organs in all orthogonal directions and smaller than 1.8 mm (range: -4.0 to 7.8 mm) for the diaphragm domes in the CC direction. For all organs and across all fractions, ranges of position variations were largest in the CC direction (varying from 10.6 to 13.0 mm) and smallest in the LR direction (varying from 4.1 to 11.1 mm) (Figure 4.2). Overall, kidney position variations were smaller than position variations of the liver and spleen (Figure 4.2). Table 4.2 presents the values of the group mean, systematic and random error per organ in each direction, mainly showing average systematic error in decreasing order of CC (3.2 mm, SD=0.3 mm), AP (1.9 mm, SD=0.9 mm), and LR (1.7 mm, SD=0.5 mm) direction, and average random error also in decreasing order of CC (3.0 mm, SD =0.5 mm), AP (2.1 mm, SD=0.6mm), and LR (1.9 mm, SD=0.7mm) direction. Differences of the systematic error between right- and left-sided organs were insignificant (p≥0.004), as were the differences of the random error between right- and left-sided organs (p≥0.004) (Supplementary Table 4.1). For superiorly and inferiorly located organs, significant but small differences were found between the liver and the right kidney in the AP direction (p=0.002 for Σ), and in the LR direction (p=0.000 for σ). Also, the random error of the spleen and the left kidney was significantly different in the AP direction (p=0.001) (Supplementary Table 4.1).
A moderate and statistically significantly correlation between the position variations of the right and left diaphragm domes was found (ρ=0.63, p=0.00) (Figure 4.3a). The position variations of the liver and spleen in the LR and CC direction were weakly, but statistically significantly correlated (ρ=0.23, p=0.02 and ρ=0.40, p=0.00, respectively) (Figure 4.3b). Position variations of the right and left kidney were weakly, but statistically significant correlated in the LR and AP directions (ρ=-0.43, p=0.00 and ρ=0.23, p=0.01, respectively) (Figure 4.3c). Correlations within each individual patient were similar to the overall group outcomes.
Linear regression analysis showed that right and left diaphragm dome position variations in the CC direction were significantly correlated with position variations of the liver (R2=0.55, p=0.00) and spleen (R2=0.63, p=0.00), respectively. In the CC direction, no (strong) correlation was found between right and left diaphragm dome position variations and the position variations of the right (R2=0.003, p=0.60) and left kidney (R2=0.25, p=0.00) , respectively (Figure 4.4).
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