RADT-81. RANDOMIZED PHASE 2 TRIAL COMPARING HYPOFRACTIONATED RADIATION THERAPY WITH SIMULTANEOUS INTEGRATED BOOST (SIB) VERSUS CONVENTIONAL RADIATION THERAPY IN GLIOBLASTOMA MULTIFORME

Abstract BACKGROUND Glioblastoma multiforme (GBM) is treated with adjuvant radiation with concurrent and adjuvant temozolomide. Hypofractionation with dose escalation using simultaneous integrated boost may tackle in-field recurrences. METHODS Between November 2023 to May 2025, 40 patients of newly diagnosed GBM were randomized between conventional radiotherapy (CRT) and hypofractionated radiotherapy (HRT). All patients received radiation therapy by volumetric modulated arc therapy (VMAT)- in conventional arm, to 60Gy in 30 fractions over 6 weeks at 2Gy per fraction, versus, in experimental arm, to 63Gy to high-risk planning target volume (PTV) defined by giving 3- 5mm margins to the gross tumor volume (GTV) and 52.5Gy to low-risk PTV defined by a clinical target volume (CTV) expansion of 15mm from the GTV with PTV margins of 3-5mm, in 15 fractions over 3 weeks with concurrent temozolomide followed by 6 cycles of adjuvant temozolomide. RESULTS At the time of assessment, 9, and 10 patients were alive in CRT and HRT arm respectively, with a total of 21 deaths. The median age was 49 years with 21 patients (52.5%) were males. The median tumor size was 4.6cm and 19 patients (47.5%) had a gross (GTR) or a near total excision (NTR). Over a median follow up of 7.5 months, the median overall survival for the entire cohort, the CRT arm and the HRT arm were 8.8 +/- 1.2 (95% CI: 6.5- 11), 7.5 +/- 3.3 (95% CI: 1- 13.9) and 8.8 +/- 0.47 (95% CI: 7.8 -9.7) months respectively (p=0.624). The median progression free survival for the entire cohort, the CRT arm and the HRT arm were 7.9 +/- 1.1 (95% CI: 5.8- 10), 7.8 +/- 2.6 (95% CI: 2.7- 12.9) and 9.9 +/- 2.1 (95% CI: 5.8-14.1) months respectively (p=0.832). CONCLUSION Longer follow up details will be necessary to assess the feasibility of HRT in the treatment of GBM.