Purpose Reconstructing 3D dose distributions for pre-1990 pediatric 2D radiotherapy plans is challenging, but key to research on late adverse effects. We studied the relation between dosimetric accuracy, anatomical variation, and other patient features of a 3D dose-reconstruction approach using CT scans of recently-treated patients, rather than phantoms. Materials and methods CT-scans of 22 Wilms’ tumor patients (age:2.5-5.3yrs; n boys/girls:11/11) treated between 2004 and 2015 were included. Two clinical plans as applied to a 4-year-old boy and girl with a left-sided Wilms’ tumor served as references. Each plan was applied to the CT scans of the other 21 patients, adjusted to correct for anatomical differences as visible in digitally-reconstructed-radiographs, and the resulting dose was calculated. Deviations in reconstructed dose, with respect to the reference dose, in organs-at-risk (spinal cord, right kidney, liver, and spleen) were characterized by the mean dose error normalized by the prescribed dose (DEmean). Deviations in organs’ location relative to a reference point (\Delta O_loc) and in organs’ shape captured by the Dice coefficient (DC) were calculated. We estimated the Pearson’s correlation between DEmean, on the one hand, and O­loc, DC, gender, age, height, and weight, on the other hand. Results Average(range) DEmean values were: spinal cord:3(0-8)%; right kidney:6(0-20)%; liver:9(0-20)%; and spleen:23(0-80)%. DC and DEmean in the right kidney were moderately negatively correlated (r2=0.41). DEmean in the liver was uncorrelated with any of the tested parameters. A positive correlation was found between Oloc and DEmean in the spleen (r2=0.68). No correlations (r2<0.2) were found between DEmean and gender, age, height, and weight. Conclusions The dose-reconstruction accuracy is primarily related to similarity in internal anatomy and not to patient features like height and weight. For a dose-reconstruction approach utilizing CT scans of recent patients, a more advanced selection strategy for the CT scan to be used is therefore needed.

Congress of Paediatric Radiation Oncology Society Association
Academic Medical Center Amsterdam

Wang, Z, Virgolin, M, Dijk, van, I.W.E.M, Wiersma, J, Ronckers, C.M, Oldenburger, F, … Alderliesten, T. (2017). Relating anatomical variations and patient features with dose-reconstruction accuracy of a 3D dose-reconstruction approach using CT scans of recently-treated children.