Virtual reality (VR) is a fast-developing technology with

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e18023 Background: Concomitant chemoradiation therapy (CRT) that includes both external beam radiotherapy (EBRT) and brachytherapy (BT) is the current standard of care in treatment of locally advanced cervical cancer (LACC). Adaptive EBRT using volumetric modulated arc technology without BT allows dose escalation and decreases toxicities. Non-brachytherapy treatment is an evolving alternative approach provides geographical radiation accuracy but the oncological outcomes still to be evaluated. Methods: Patients with LACC (stages 1B3–IVA) who underwent non-brachytherapy CRT using adaptive EBRT with simultaneous integrated boost at our institution were evaluated prospectively from May 2015 to December 2019. All patients were initially assessed by a gynecologic oncologist, pelvic MRI and 18FDG-PET/CT scan were conducted. Follow-up pelvic examinations with cytology every 3 months and PET/CT at 3 and 12 months after completion of treatment were performed. Oncological outcomes and toxicities were assessed. Results: Twenty-one patients were analyzed: median age was 54 years (30–76 years); 19 patients had squamous cell histology and 2 had adenocarcinoma. Median follow-up was 32 months (8–56). The average dose administered to the gross tumor volume was 90.2 Gy (79.5–96.6), 79.8 Gy to all PET/MRI positive lymph nodes (63.0–89.7). No patents received BT; all but 3 received chemotherapy. Three-year local control was 100% (PFS = 90.4% and OS = 100%). There were 2 recurrences: a solitary skull lesion 18 months following CRT in a patient with mesonephric adenocarcinoma and a metastasis to a transposed ovary 15 months after CRT. No grade 3–4 toxicities were seen. Only 1 patient (4.7%) had late rectal grade II toxicity. Conclusions: Non-brachytherapy adaptive CRT for LACC is feasible. It allows for a significant dose escalation, thus providing better local control and likely increases PFS and OS at no cost of serious toxicity. Randomized studies comparing this approach to the current standard of care are needed.

2535 Background: Glioblastoma multiforme (GBM) is an extremely aggressive cerebral tumor with poor prognosis. The majority of patients relapse after the initial surgery plus adjuvant radiation and chemotherapy. In case of recurrence there is no established standard therapy. The optimal techniques for salvage re-irradiation are unclear, so that procedure poses a challenge. In contrast to traditional external beam radiotherapy (EBRT) intra-operative radiotherapy (IORT) may improve patient’s outcome at the cost of minimal side effects and short treatment duration. Methods: A total of 30 patients were treated with recurrent GBM between August 2016 and June 2019. All patients underwent maximal safe resection; patients were divided into IORT and EBRT groups. 15 patients were included in each group with similar clinical characteristics. All patients in IORT group underwent maximal safe microsurgical resection with subsequent intraoperative balloon electronic brachytherapy (IBEB) and no further adjuvant treatment. IBEB was performed using Axxent electronic brachytherapy device (Xoft Electronic Brachytherapy (eBx) System, USA. Patients in EBRT group underwent same surgery followed by external beam radiotherapy. Contrast-enhanced brain MRI with perfusion was performed within 24 hours of surgery +/- brain PET-CT with 18-FDOPA and then every 3 months. Both groups were also assigned to subgroups (≤ 2.5cm3 and > 2.5cm3) based on post-operative contrast-enhancing volume (POCEV). Median overall survival (OS) since diagnosis and local progression-free survival (locPFS) following the second surgery were analyzed. Possible toxicities and prognostic factors were also evaluated. Results: Median OS was 27 months in IORT group and 21 months in EBRT group. The locPFS range between 3.5 to 39 months in IORT group and only 2 to 10 months in group with EBRT. Kaplan-Meier OS curves in patients with POCEV ≤ 2.5cm3 showed more favorable outcomes for patients in the IORT group (p < 0.05). In patients with POCEV > 2.5cm3 the median OS was 17 months in IORT group and 13.5 months in EBRT group. Conclusions: IORT of recurrent GBM is feasible and provides encouraging local progression-free and overall survival; no high-grade radiation induced toxicities occur and further studies to establish this method are mandatory. The toxicity profile of additional IBEB was manageable. Maximal safe microsurgical resection is the most important prognostic factor and could determine the effectiveness of post-surgical IBEB.