ESTRO 2021 Abstract Book

S863

ESTRO 2021

T1c:FLAIR ratio 0.1

0.3 0.2 (0.1, 0.2)

Conclusion We did not find a significant association between molecular profile and early post-radiotherapy volumetric changes in high grade diffuse astrocytoma. Increase in post-chemoradiation FLAIR volume without increase in contrast or perfusion in IDH wild-type patients is likely post-treatment change. Further exploration of delta radiomics is justified. PO-1034 Hypofractionated Radiotherapy and Simultaneous Boost in radically inoperable cases with Glioblastoma F. Gregucci 1 , I. Bonaparte 1 , A. Surgo 1 , R. Carbonara 1 , M.P. Ciliberti 1 , G. Masiello 1 , R. Tucciariello 1 , M. Caliandro 1 , A. Fiorentino 1 1 Miulli General Regional Hospital, Radiation Oncology, Acquaviva delle Fonti - Bari, Italy Purpose or Objective Aim of this study was to evaluate efficacy and toxicity of hypofractionated radiotherapy (hypoRT) with simultaneous integrated boost (SIB) associated with concomitant and adjuvant temozolamide (TMZ) in radically inoperable patients affected by Glioblastoma (GBM). Materials and Methods Patients with a newly diagnosis of GBM not eligible for maximal safe surgical resection were evaluated in this retrospective study. If possible, a subtotal resection was performed or alternatively an open biopsy followed by hypoRT with SIB and concomitant plus adjuvant TMZ (75mg/mq every day during RT and 150-200 mg/mq for 5 days every 28-day cycle, respectively). The prescription dose for hypoRT was 40.05 Gy in 15 fractions on planning target volume (PTV) with a SIB of 52.5 Gy (3.5 Gy per fraction) on residual/macroscopic disease identified as gross tumor volume (GTV). GTV was defined as the macroscopic disease detected on T1 contrast sequence on MRI. The clinical target volume (CTV) was defined adding to GTV an isotropic margin of 1-1.5 cm, respecting the anatomical barriers and organs at risk (OaRs). The margins CTV-PTV were assigned of 3 mm. In each case, the contouring of target and OaRs was performed using a rigid fusion between MRI and planning CT. Flattening Filter Free (FFF) and Volumetric Modulated Arc Therapy (VMAT) technique with 2 or more coplanar or non-coplanar arcs were generated for each treatment plan. The primary endpoints were overall survival (OS) and progression free survival (PFS). Secondary endpoint was toxicity. Results From September 2019 to January 2021, 20 patients (8 female and 12 male) were treated in our Department, according to study criteria. The median age was 64 years (range 37-82) and median ECOG was 2 (range 1-3). All patients have histological diagnosis of GBM IDH1 wild-type and 30% of cases showed MGMT methylation, 15% were not methylated and in 55% MGMT status was unknown. Subtotal resection was performed in 14 patients (70%) while biopsy in 6 (30%). The median time occurred between surgical procedure and RT was 56 days (range 15-103). The median GTV_52.5Gy was 45cc (range 13-208). The median PTV_40.05Gy was 208cc (range 84-330). At median follow-up time of 10 months (range 2-18), the median OS was not achieved (95%CI 6.06-na) and 1-year OS was 75.8% (95%CI 47.2-90.3); the median PFS was 9.8 months (95%CI 5.63-na) and 1- year PFS was 24.1% (95%CI 1.62-61.2). The Kaplan-Meier curves for OS and PFS are showed in Figure 1. Regarding toxicity no acute or late neurological side effect grade ≥ 2 were reported. In all cases, prophylactic steroid therapy was administrated. Grade 3-4 hematologic toxicity occurred in 3 cases.

Conclusion