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Inter- and Intra-Fraction Motion Uncertainties During IGRT for Kidney Tumor in Pediatrics

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F Guerreiro

F Guerreiro*, E Seravalli , G Janssens , B Raaymakers , Department of Radiotherapy and Imaging Division, University Medical Center Utrecht, The Netherlands


SU-I-GPD-J-32 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The aim of this study is to assess inter- and intra-fraction biological uncertainties, due to motion of the tumor bed (TB) and organs at risk (OARs), as well as physical uncertainties, due to patient positioning variations, during image-guided radiation therapy (IGRT) in children with kidney tumor (Wilms’ tumor).

Methods: Computed tomography (CT), 4D-CT and daily cone-beam CTs (CBCTs) of 15 pediatric patients undergoing flank irradiation were analysed.TB (marked by 4 surgical clips) and OARs motion was quantified by displacements of the center of mass (CoM) in all orthogonal directions. For inter-fraction motion assessment, CoM displacements were calculated using the planning-CT as reference and daily pre-treatment CBCTs. Intra-fraction motion was estimated by calculating the CoM displacements between the maximum inspiration and expiration phases of the 4D-CT. For assessing the physical uncertainty, translational bone off-sets were recorded. Patient positions were corrected online using the automated treatment table movement. As rotations were not accounted for, a residual inter-fraction patient positioning error was denoted. To assess this, the off-set between the pre-treatment CBCT and the correction applied to the table was calculated. For intra-fraction uncertainty, off-sets were calculated between the planning-CT and the post-treatment CBCTs. Average results and systematic and random errors were determined.

Results: Average CoM displacements for biological uncertainties were ≤3.2 mm in magnitude. Maximal individual CoM displacements were ≤7.9 mm for the TB and ≤9.6 mm for the OARs. Average physical uncertainty was ≤0.1 mm in magnitude. Systematic and random errors were ≤2.4 mm for biological and ≤0.8 mm for physical uncertainties.

Conclusion: Biological and physical uncertainties during treatment were found to be limited. With IGRT, the use of patient specific margins is advised for both planning target volume and OARs. This study represents a first-step towards improving guidelines for abdominal pediatric tumors.

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