ESTRO 2021 Abstract Book

S48

ESTRO 2021

Conclusion Our results identified an area of tumor localization in the left temporal region that was significantly associated with subsequently evoked post-radiation injury. Further exploration of the role of the spatial distribution of gliomas could elucidate the etiology of radiation treatment complications and guide neurosurgery and radiation treatment modality strategies, based on pre-operative tumor location. OC-0075 Dual FET PET-guided SIB in radiotherapy of newly diagnosed glioblastoma- a pilot study. M. Harat 1 , M. Blok 2 , I. Wiatrowska 3 , B. Małkowski 4 1 Franciszek Lukaszczyk Memorial Oncology Center, Neurooncology and Radiosurgery, Bydgoszcz, Poland; 2 Franciszek Lukaszczyk Memorial Oncology Center, Radiotherapy, Bydgoszcz, Poland; 3 Franciszek Lukaszczyk Memoriał Oncology Center, Medical Physics, Bydgoszcz, Poland; 4 Franciszek Lukaszczyk Memorial Oncology Center, Nuclear Medicine, Bydgoszcz, Poland Purpose or Objective Positron emission tomography (PET) using the radiotracer – (18F-fluoro-ethyl-tyrosine) is a valuable tool to determine the actual glioblastoma infiltration .The FET-PET examination can be performed using the dual- time point aqusition of FET (dual FET PET). Infiltration defined in dual FET PETcorresponds to the location and shape of the recurrence. The aim of this study was to evaluate safety and efficacy of simultaneus integrated boost based on dual FET PET combined with temozolomide for the postoperative treatment of GBM. Materials and Methods In a prospective pilot study (March 2017 to December 2020), 17 patients were qualified for radiochemotherapy after partial resection. All patient presented an active tumor in postoperative (preirradiation) PET imaging. The radiotherapy was performed as an FET-PET-based simultaneous integrated boost IMRT. The prescribed dose was 78 and 60 Gy (single dose 2.6 and 2.0 Gy, respectively) for the FET-PET- and MR-based target volumes. MRI were performed routinely for follow-up. Eleven patients had FET-PET done within 9 months after irradiation to precisely defined the biologic response. The progression-free survival (PFS) and overall survival (OS), toxicities and 3-months radiation necrosis rate were evaluated. Results Results: The median follow up was 37 months (24- 46) Two patients were found to have serious adverse effects (uncotrolled seizures) during radiation treatment and were not able to recived treatment per protocol. Patients treated per protocol presented new or increased neurological deficits in 7/15 cases in a month after irradiation. In MRI 3 months after SIB 5 patients were diagnosed with radiation necrosis. Three patients were still alive after 26,28 and 38 months of follow up without progression and any signs of treatment related late toxicity. The 2-year survival rate was 43% in all patients treated per protocol. Median overall survival (OS) and disease-free survival (DFS) were 20 and 12 months, respectively. In a subgroup of MGMT methylated and unmethylated the median survival was 25 months and 12 months, respectively(censored). In 2 patients tumor was largrer in FET-PET after treatment (3-9months). Conclusion Our dose escalation concept with a total dose of 78 Gy, based on FET-PET, have led to promising survival results even within MGMT unmethylated subgroup . However rate of early toxicity and radiation necrosis is high.