Abstract Book

ESTRO 37

S369

Results After median follow up of 20,3 months (range 0,1–77 months), the local control rate was 96% after a primary HFSRT and 90% after re-irradiation. All asymptomatic patients retained their status after treatment. The clinical control rate of symptoms in the overall population was 95% (95% CI: 89-98%). After a median time of 4.4 months (1.1-21.3 months), the objective clinical response rate (partial and complete responses) is 51% (95% CI: 50- 60%). Progression-free survival (PFS) in the overall population at 24 month was 71.5% (95% CI: 61.1% - 79%). PFS was significantly better in primary HFSRT patients group (80% vs 40%, p = 0.002). In this group, PFS was significantly associated with the radiotherapy schedule, PFS was significantly lower with the most hypo fractionated schedules (21-23 Gy in 3 fractions vs 25-40 Gy in 5-10 fractions: 62% vs 92%, p=0.0006). The overall survival rate at 24 months in the whole population is 96% (95% CI: 88-98%); there was no statistically difference between the primary and re-irradiated group (p = 0.31). Tolerance was satisfactory; grade 1 (26%) and 2 (5 %) acute toxicity was recorded to the maximum. The incidence of radionecrosis at 24 months was significantly lower in primary HFRST group 2% vs 20% in re irradiation HFRST (p=0.002). Conclusion We report a satisfactory rate of LC and PFS with a favorable tolerance profile. HFSRT of intracranial meningioma is feasible as first line treatment, and as a re irradiation approach in management of relapse. Obviously, studies with a longer follow-up are essential to confirm our findings. PO-0722 Radiosurgery in association with immunotherapy for NSCLC brain metastases: feasibility and results L. Schiappacasse 1 , S. Alshehri 1 , R. Jumeau 1 , C. Tuleasca 2 , F. Ahmad 1 , N. Mederos 3 , H. Bouchaab 3 , M. Levivier 2 , J. Bourhis 1 1 Centre Hospitalier Universitaire Vaudois, Department of Radiation Oncology, Lausanne Vaud, Switzerland 2 Centre Hospitalier Universitaire Vaudois, Department of Neurosurgery, Lausanne Vaud, Switzerland 3 Centre Hospitalier Universitaire Vaudois, Department of Medical Oncology, Lausanne Vaud, Switzerland Purpose or Objective Introduction: Recent reports suggest that immune checkpoint therapy (ICT) combined with stereotactic radiosurgery (SRS) have been associated with greater lesion regression of melanoma brain metastases and decreased local failure. When given concurrently (within 4 weeks), combined SRS and ICT may result in improved freedom from additional new brain metastases. Objective: To investigate the feasibility and efficacy of ICT administered with SRS in patients with brain metastases of non small cell lung cancer (NSCLC) and evaluate if synergistic effect observed for melanoma is also identified in these patients. Material and Methods 101 individual patients with brain metastases from lung cancer, being treated 185 times by SRS between March 2014 and November 2016, and followed in the prospective cohort of the brain metastases clinic at the CHUV where included in this analysis. Systemic treatment use within 6 weeks of SRS was noted. The prescription was 20 Gy in single fraction or 33 Gy in 3 fractions, according to the volume of PTV. Results Among the 185 SRS performed, 66 corresponded to single metastases, 48 to 2 - 4 metastases, 27 to 5 - 10, and 10 to > 10 in every single event. The median volume for the PTV was 1,68 ml, the average volume 10,17 ml. Fifty-six patients received only one treatment, 29 of them two

and 16 three or more (max. 5). 1-year OS was 56,11% and 68,06% for patients in the chemotherapy and immunotherapy groups, respectively (p=0,26); 1-year brain-DFS was 32,16% (chemotherapy) and 31,02% (immunotherapy; p=0,95). Toxicity was minimal, with 3% grade 2 and no adverse event > grade 2. Conclusion SRS in combination with ICT is feasible, without an increase in toxicity. Even if there was a trend for improvement of OS between patients treated with immunotherapy, the brain-DFS was identical in both groups, suggesting that there was no synergistic effect between ICT and SRS in patients with brain metastases of NSCLC. PO-0723 TSPO-PET for RT treatment planning using [18F]GE-180 – first in human results in GBM p atients M. Niyazi 1 , D.F. Fleischmann 1 , M. Unterrainer 2 , P. Bartenstein 2 , N.L. Albert 2 , C. Belka 1 1 LMU Munich, Dep. of Radiation Oncology, Munich, Germany 2 LMU Munich, Dep. of Nuclear Medicine, Munich, Germany Purpose or Objective The 18-kDa mitochondrial translocator protein (TSPO) was reported to be upregulated in glioblastomas. [ 18 F]GE- 180 is a novel 3rd generation TSPO receptor ligand with improved target-to-background contrast compared to previous tracers. Therefore, we intended to evaluate the feasibility of [ 18 F]GE-180 PET in glioblastoma patients and its potential use for radiotherapy (RT) planning and prognostication. Material and Methods 12 patients with histologically confirmed IDH wildtype gliomas (11 glioblastomas, 1 anaplastic astrocytoma IDH wildtype) underwent 18 F-GE-180 PET at initial diagnosis or recurrence prior to radiotherapy. Analysis of TSPO polymorphism excluded low-affinity binders. The PET parameters mean background uptake (SUV BG ), maximal tumor uptake (SUV max ), maximal tumor-to-background ratios (TBR max ) and biological tumor volumes (BTV) using different thresholds (SUV BG x 1.6, 1.8 and 2.0) were evaluated in the 60-80 minutes p.i. summation images. The different PET volumes were compared to the MRI- based gross tumour volume (GTV) used for radiotherapy planning. Results All glioblastomas showed [ 18 F]GE-180 uptake with high tumor-to-background contrast (median SUV max 3.1 (2.5 – 5.8) and TBR max 6.9 (3.9 – 9.1). Volumetric comparisons with MR images revealed significantly larger BTVs than MRI-based GTVs (p=0.002/0.003/0.008) with high [ 18 F]GE- 180 binding even in areas without contrast enhancement on MRI. The spatial volumetric correlation (Sørensen-Dice coefficient) of BTVs and GTV prior to radiotherapy was 0.48 (BTV1.6), 0.54 (BTV1.8) and 0.58 (BTV2.0). After radiotherapy, the analyzed patients showed a significant reduction of SUV max (median percental reduction of 43.4% (1.1% - 61.1%), p=0.012) and of TBR max (median percental reduction of 27.9% (14.1% – 54.8%), p=0.012). Additionally, significant reductions of the BTVs could be observed in all but one patients (e.g. median percental reduction of BTV1.6: 63.2%, p=0.017). Altogether, 2/8 patients showed a nearly complete remission of the extent of TSPO expression (92.0% and 94.7%) and 5 patients in a range between 26.1% and 63.2%, whereas 1 patient showed an increase of 34.8% despite the previous radiotherapy. Conclusion This first study using the novel TSPO ligand [ 18 F]GE-180 in glioma patients shows a remarkably high tumor-to- background contrast of [ 18 F]GE-180 PET scans in glioblastoma. As high TSPO expression was shown even in