ATRT-10. EARLY POST RADIATION CHANGES AND EFFICACY IN CHILDREN WITH ATRT TREATED ON COG ACNS 0333: A COMPARISON OF PROTON VS PHOTON THERAPY

Abstract

Abstract BACKGROUND/OBJECTIVES: COG ACNS0333 is a prospective study evaluating surgery, intensive chemotherapy and radiation therapy (RT) in the management of ATRT. The therapy sequence was based on patient age, disease location and extent. Both proton RT (PRT) and photon RT (XRT) modalities were permitted. In this study the early post-RT changes and efficacy of PRT and XRT were compared. METHODS: All RT plans were reviewed centrally. Pre-operative, post-operative, pre-RT and first post-RT MRI scans were available and reviewed. Patient characteristics, treatment sequence, RT plan, tumor volume, brain and brainstem dosimetric parameters were evaluated. RESULTS: 41 of 65 evaluable patients on protocol received RT between 5/2009 and 11/2013 (14 PRT, 27 XRT). Median age at RT was 1.7y (range 0.6 – 13.9y). 6/41 patients received craniospinal RT. Median tumor dose was 50.4Gy (range 45-54Gy). All patients had >1 post-RT MRI scans available. At a median post-diagnosis follow up of 9 months, tumor control was equivalent after PRT and XRT (p=0.83). At a median post-RT follow up of 5 months (range 1.4–36.1) 10/42 patients had in-field MRI changes of varying severity (3 PRT, 7 XRT) in the absence of clear tumor progression. These MRI changes were noted between 2–6 months post-RT. Patients with post-RT MRI changes tended to have larger tumors with larger pre-operative tumor volume (median 137 cc vs 57 cc) and larger CTV’s (median 257cc vs 125 cc); however, the difference was not statistically different (p=0.21). CONCLUSION: In this early analysis of COGACNS 0333 there were no detectable differences in tumor control between the patients treated with PRT vs XRT. Reactive changes were seen with both modalities but were not excessive with either.