Quantification of renal and diaphragmatic interfractional motion in pediatric image-guided radiation therapy: A multicenter study

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BACKGROUND AND PURPOSE: To quantify renal and diaphragmatic interfractional motion in order to estimate systematic and random errors, and to investigate the correlation between interfractional motion and patient-specific factors. MATERIAL AND METHODS: We used 527 retrospective abdominal-thoracic cone beam CT scans of 39 childhood cancer patients (<18years) to quantify renal motion relative to bony anatomy in the left-right (LR), cranio-caudal (CC) and anterior-posterior (AP) directions, and diaphragmatic motion in the CC direction only. Interfractional motion was quantified by distributions of systematic and random errors in each direction (standard deviations Sigma and sigma, respectively). Also, correlation between organ motion and height was analyzed. RESULTS: Inter-patient organ motion varied widely, with the largest movements in the CC direction. Values of Sigma in LR, CC, and AP directions were 1.1, 3.8, 2.1mm for the right, and 1.3, 3.0, 1.5mm for the left kidney, respectively. The sigma in these three directions was 1.1, 3.1, 1.7mm for the right, and 1.2, 2.9, 2.1mm for the left kidney, respectively. For the diaphragm we estimated Sigma=5.2mm and sigma=4.0mm. No correlations were found between organ motion and height. CONCLUSIONS: The large inter-patient organ motion variations and the lack of correlation between motion and patient-related factors, suggest that individualized margin approaches might be required.