ESTRO 2022 - Abstract Book

S957

Abstract book

ESTRO 2022

1 Univerity Hospital Birmingham, Oncology, Birmingham, United Kingdom; 2 University Hospital Birmingham, Oncology, Birmingham, United Kingdom; 3 University Hospital Birmingham, ENT, Birmingham, United Kingdom; 4 University Hospital Birmingham, Neurosurgery, Birmingham, United Kingdom; 5 University Hospital Birmingham, Radiology, Birmingham, United Kingdom Purpose or Objective Stereotactic radio-surgery (SRS) is routinely used to treat Vestibular Schwannoma’s (VS) to avoid the need for surgical intervention. However, some VS can remain indolent and given that SRS carries a risk of toxicity without guarantee of long term hearing preservation, timing of intervention remains debated. The objective of this analysis was to assess toxicity and long term outcomes using CyberKnife SRS. Materials and Methods All patients undergoing SRS for VS at a regional centre were identified from a prospective database. Patients with progressive growth on an observation programme, or presenting with a tumour ≥ 2cm, and minimum 5 year follow up were included. Patients with prior surgical intervention were excluded. The prescription dose was either 12 Gy in 1 fraction to 100% of PTV, or 18Gy in 3 fractions. The primary endpoint was progression defined as need for surgical salvage. Secondary endpoints included any grade of facial and trigeminal nerve toxicity. All other CTCAEv4 grade 3 or 4 toxicity events were recorded. All patients were given a key worker contact number to report toxicity events. Results 130 patients were included for analysis. 126 were treated with a single fraction and 4 were treated with 3 fractions. Mean size was 1.78cc (range 0.14cc-9.44cc). 7 patients required surgery for progression. All patients with failure received a single fraction. In patients requiring surgery the mean tumour volume was 3.11cc (0.6cc-5.28cc) vs. 1.70cc (0.14cc-9.44cc) in those who did not (p=0.035). 9 patients experienced some form of acute facial nerve toxicity and 2 (1.5%) were persistent. There was no association between volume and acute facial nerve toxicity (p=0.37). 20 patients had acute trigeminal toxicity, all of which received treatment in a single fraction and 3 persisted beyond 2 years. 4 additional patients developed late trigeminal toxicity, 2 of which persisted leaving a total of 5 patients with persistent trigeminal nerve toxicity (3.8%). In patients with acute trigeminal toxicity the mean volume was 2.63cc (0.49cc-6.67cc) vs 1.63cc (0.14cc-9.44cc) in those who did not have toxicity (p=0.016). Similarly the mean trigeminal nerve dose was 1085cGy vs 872cGy in those with/without toxicity (p=0.01). Conclusion The trend of increased risk of failure for larger volume VS should be considered when following a policy of observation. Although long term toxicity rates were low, significant levels of temporary nerve irritation were seen. Consideration should also be given to whether the trigeminal nerve constraint will still be achieved if delaying SRS. 1 General Regional Hospital F Miuli, Radiation Oncology , acquaviva delle fonti, Italy; 2 General Regional Hospital F Miulli, Radiation Oncology, Acquaviva delle fonti, Italy; 3 General Regional Hospital F Miulli, Radiation oncology, acquaviva delle fonti, Italy; 4 General Regional Hospital F Miulli, Radiation Oncology, acquaviva delle fonti, Italy Purpose or Objective Glioblastoma (GBM) is a very poor prognosis brain tumor. To date, maximal excision followed by radiochemotherapy, in 30 fractions, is the standard approach. Limited data are present in literature about hypofractionated radiotherapy (hypoRT) in GBM poor prognosis patients, other than advanced age. Thus, this retrospective study was conducted to evaluate efficacy and toxicity of hypoRT with simultaneous integrated boost (SIB) in association with temozolamide (TMZ) in this setting of patients. Materials and Methods GBM poor prognosis patients underwent surgery (complete, subtotal or biopsy) followed by SIB-hypoRT and concomitant/adjuvant TMZ. The definition of poor prognostic factors other than advanced age, included KPS or RPA class, neurological symptom after surgical procedures or symptoms of mass effect, high tumor burden, unresectable or multifocal lesions, high comorbidity and potential low treatment compliance due to rapidly progressive disease. The prescription dose was 40.05Gy (15 fractions) with a SIB of 52.5Gy (3.5Gy/fraction) on surgical cavity/residual/macroscopic disease. Volumetric Modulated Arc Therapy was performed. Results From July 2019 to July 2021, 30 poor prognosis patients affected by GBM were treated by SIB-hypo-RT; 25 were evaluated in the present analysis due to a minimum follow up of 6 months. The median age and KPS were 65 years and 60%, respectively. At 15 months median follow-up, 14 patients (56%) were alive: 3 (12%) showed partial treatment response, 3 (12%) with stable disease and 8 (32%) with progression disease. The median OS was 13 months (95%CI 9.8-na) and 1-year OS was 54% (95%CI 31-73%); the median PFS was 8.4 months (95%CI 5.8-11.9) and 1-year PFS was 23% (95%CI 7-44%). No acute or late neurological side effect grade ≥ 2 were reported. Grade 3-4 hematologic toxicity occurred in 3 cases. Of the 17 cases of disease progression, 8 received re-irradiation followed by second line systemic therapy (regorafenib or fotemustine), 3 received regorafenib alone and 6 were evaluated for best supportive care Seven significant variables in univariate analysis (age, RPA, multifocal tumor, resection, MGMT status, GTV and PTV) were entered into multivariable model. As a result, MGMT unmethylation (HR: 0.61, 95%CI: 0.02-13.66, p=0.05), GTV > 50cc (HR: PO-1126 Hypofractionated radiotherapy in poor prognosis patients affected by glioblastoma A. Fiorentino 1 , A. Surgo 2 , I. Bonaparte 3 , M.P. Ciliberti 2 , R. Carbonara 4 , M. Caliandro 2 , F. Gregucci 4