Dosimetric effect of target expansion and setup uncertainty during radiation therapy in pediatric craniopharyngioma

PurposeInvestigate the effect of tumor change and setup uncertainties on target coverage for pediatric craniopharyngioma during RT.Methods and materialsFifteen pediatric patients with craniopharyngioma (mean 5.1 years) were included in this study. MRI was performed before and a median of six times during RT to monitor changes in the tumor volume. IMRT plans were created and compared to the CRT plan used for treatment. The role of adaptive therapy based on GTV changes was investigated. Dosimetric effects of interfraction and intrafraction motion were examined.ResultsThe mean of the maximal change in the GTV was 28.5% [−20.7% to 82.0%]. For the standard margin IMRT plans, the mean D95 of the base plan on the base target was 53.6 Gy [53.1–54.1]. The mean D95 of the base plans on the adaptive targets was 52.1 Gy [47.9–54.1]. The D95 for the adaptive plan on the adaptive target was 53.8 Gy [53.4–54.3]. A linear regression equation of y=-0.12xy=-0.12x , r2 = 0.70, was found for the percent change in D95 of the PTV (y) vs. the percent change in the GTV (x). Inter and intrafraction motion did not affect the target coverage for standard and reduced margin plans.ConclusionsThe GTV of pediatric craniopharyngioma patients change size during therapy and adaptive planning is critical for conformal plans; therefore early and regular surveillance imaging is required.