SU-E-T-495: Proton Therapy for CNS Atypical Teratoid Rhabdoid Tumor in Children under Three

Abstract

Purpose: Investigate the possible benefits of treating patients younger than three years of age with central nervous system(CNS) atypical teratoid/rhabdoid tumors (AT/RT) with proton therapy, both double scattering (DS) and intensity modulated proton therapy (IMPT), over intensity modulated photon therapy (IMRT). Method and Materials:CNS AT/RT is a rare, aggressive embryonal tumor with an incidence approaching 20% in children under the age of three with CNSmalignancies. Data from five patients with a mean age of 1.0 years recently treated in our clinic were used for this study. The average time between diagnosis and radiation therapy was three months. DS, IMPT, and IMRTtreatment plans were generated for each patient, ensuring proper coverage of the target (98% of PTV receives 98% dose) for each modality. Special consideration of margin selection for the proton plans was used. Dose heterogeneity in the target, conformality to target, dose to critical structures, dose to normal brain, and integral dose were examined. Results: Preliminary data indicates that given full target coverage, DS has the smallest dose heterogeneity within the target and IMRT the largest. Conformality for IMPT was largest and DS lowest for the most part, however, since larger margins were utilized for proton planning more investigation is required. On average, the dose to critical structures, normal brain, and integral dose was smallest for IMPT, followed by DS, and largest for IMRT. Conclusion: Preliminary data indicates that dose to critical structures, integral dose, and the dose to normal brain is reduced with proton therapy; therefore implying merit in this modality. This dose sparing is crucial because of the high sensitivity of normal tissues for very young patients.