Feasibility of cognitive sparing approaches in children with intracranial tumors requiring partial brain radiotherapy: A dosimetric study using tomotherapy

Background : To assess feasibility of sparing the neural stem cell compartment (NSC), hippocampus, and limbic circuit during partial brain radiotherapy (PBRT) for pediatric intracranial tumors. Methods : Treatment plans were generated for the following pediatric intracranial tumors: low and high grade gliomas, low grade brainstem glioma, optic nerve glioma, hypothalamic glioma, localized ependymoma, skull base sarcoma, central nervous system (CNS) germinoma (involved field radiotherapy [IFRT] and whole ventricular radiotherapy [WVRT] ), and craniopharyngioma. For each pathology, standard intensity-modulated radiotherapy (IMRT) plans were generated using helical tomotherapy, as well as IMRT plans which spared limbic circuit, hippocampus, and NSC. Biologically equivalent dose for late effects (BEDlate effects) was generated for limbic circuit, hippocampus, and NSC. Percent reduction in mean, maximum, and minimum physical dose and BED was calculated between plans. Results : We reduced mean physical dose and BEDlate effects to these critical structures by 44% and 47.9% respectively (range 5.4-78.8% and 7-80.3%). Greatest benefits in relative dose reduction were seen in high grade hemispheric glioma cases; least relative dose reduction was seen in WVRT cases. Dosimetric coverage of treatment target (PTV) was equivalent in all cases as assessed by D95 and V100 metrics. Integral dose to uninvolved brain was reduced by mean of 7.6% (range -19.3% to +0.3%) in sparing plans. Discussion and Conclusions : It is possible to spare limbic circuit, NSC, and hippocampus during PBRT for primary pediatric intracranial tumors using helical tomotherapy. This approach reduces integral dose delivered to uninvolved normal brain and may reduce late cognitive sequelae of cranial radiotherapy.