Page 106 - Organ motion in children for high-precision radiotherapy - Sophie Huijskens

6.3 | Results
The differences in respiratory-induced diaphragmatic motion parameters between children and adults are summarized in Figure 6.1. The mean amplitude was slightly smaller in children than in adults (average: 10.7 mm vs. 12.3 mm, range: 4.1-17.4 mm vs. 5.1-24.4 mm), however statistically insignificant (p=0.06). Interfractional amplitude variability was statistically significantly smaller in children than in adults (average: 1.4 mm vs. 2.2 mm, range: 0.3-3.9 mm vs. 0.4-7.2 mm; p=0.00). Mean cycle time was statistically significantly shorter in children (average: 2.9 s vs. 3.6 s, range: 2.1-3.9 s vs. 2.7-6.5 s; p=0.00), since children breath faster than adults. Additionally, intrafractional cycle time variability was statistically significantly smaller in children (0.5 s vs. 0.7 s, range: 0.2-1.5 s vs. 0.2-3.2 s; p=0.00). The intrafractional amplitude variability was significantly smaller in children treated under GA (1.6 mm) than in children of similar ages treated without GA (2.4 mm), other respiratory-induced diaphragm motion characteristics did not differ (Figure 6.2). The repeated analysis, with exclusion of the children treated under GA, did not change our results, when comparing children and adults.
Possible relationships between respiratory-induced diaphragm motion parameters and patient-specific factors, over continuous values of age, height, and weight, are given in Figure 6.2 and Supplementary Figure 6.2. All correlations of mean amplitude and mean cycle time with age, height, and weight were statistically significant (p<0.05). However, values of Spearman’s correlation coefficients were low (amplitude ρ≤0.30; cycle time ρ≤0.50). Correlations of inter- and intrafractional amplitude and cycle time variabilities with patient-specific factors were all statistically insignificant, except for interfractional amplitude variability with age (p=0.00; ρ=0.36) and weight (p=0.04; ρ=0.22), and intrafractional cycle time variability and age (p=0.00; ρ=0.34).
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