RTHP-14. PSEUDOPROGRESSION IN HIGH GRADE GLIOMA PATIENTS AFTER PROTON OR PHOTON THERAPY

Abstract

Abstract Pseudoprogression is defined as the appearance of false progression on MR imaging following radiation therapy. Proton therapy is thought to have increased relative biological effectiveness-the ratio of the doses required by two types of radiation to cause the same level of effect-near the edges of the high dose volume. This could lead to different rates of pseudoprogression for protons compared to photons. In our IRB approved study, a board-certified neuroradiologist reviewed serial imaging of 74 patients (photons: n=37, protons: n=37) treated from 2013–2018 with either proton or photon radiotherapy to 59.4–60 Gy in 30–33 fractions and temozolomide for high grade glioma. MR imaging was performed 1 month after completion of treatment and then every 3 months. True progression was scored based on updated RANO criteria. Pseudoprogression was determined if imaging improved without change in therapy. Cumulative incidences of these outcomes and survival were calculated utilizing Kaplan-Meier analyses. Patient and treatment factors were analyzed for their association with incidence of pseudoprogression. Median follow-up for alive patients in the proton and photon groups were 15 and 29 months, respectively. Median age was 49 years in the proton group and 54 years in the photon group (p=0.17). Among proton patients, 14 had grade III glioma and 23 had grade IV glioblastoma. Among photon patients, 1 had grade III glioma. Median survival was 23 and 35 months for the proton and photon groups, respectively (p=0.57). The cumulative incidence of pseudoprogression was 14.4% and 10.4% at 12 months for the proton and photon groups, respectively (p=0.53). Grade, extent of resection, age, and IDH status, were not significantly associated with development of pseudoprogression. MGMT methylated tumors showed a trend toward association with pseudoprogression compared to unmethylated tumors (p=0.058). We concluded that the incidence of pseudoprogression is similar regardless of whether proton or photon therapy was utilized.