ESTRO 2020 Abstract book

S529 ESTRO 2020

Conclusion The present analysis shows that it is not possible to demonstrate a certain correlation between the use of the mobile phone and the onset of malignant tumors of the brain. This analysis confirms what recently published by the ISTISAN 19/11 report. PO-0904 Irradiated brain volume is not related to the risk of radionecrosis: reconsidering the role of V12Gy D. Versnel 1 , S.H. Nagtegaal 1 , A. Claes 1 , E. Seravalli 1 , J.J. Verhoeff 1 1 UMC Utrecht, Radiotherapy, Utrecht, The Netherlands Purpose or Objective Cerebral radionecrosis (RN) after stereotactic radiotherapy (SRT) remains a common complication for patients with intracranial tumours. Several studies in search of prognostic factors for RN have found a relation with irradiated brain volume. Since then, SRT treatment protocols have suggested limiting the volumes receiving specific radiation doses, in particular V10Gy and V12Gy. In order to validate this finding, we have investigated whether the brain volume receiving a specific dose correlates with the risk of cerebral radionecrosis in patients with solitary brain metastases. Material and Methods In this retrospective cohort study 126 patients with solitary cerebral metastases were treated with linear accelerator based stereotactic radiosurgery at the University Medical Center Utrecht. Excluded were patients deceased before the follow-up MRI examination and patients receiving multiple cerebral radiation-based treatments. Chi-squared tests or univariable logistic regression and multivariate logistic regression were performed on variables suspect for causing RN, in order to evaluate their predictive values. There was a focus on brain volumes receiving a specific dose (V5Gy – V20Gy), which have been analysed in two ways: continuous with absolute volumes, and dichotomised according to thresholds proposed in previous studies. Results Median overall survival was 14.2 months and RN occurred in 25 (19.8%) of treated patients. The median prescribed dose was a single fraction of 21 Gy to the 100% isodose, equivalent to EQD2 (a/b=2)87.7 Gy (range: 60 Gy - 156 Gy). Non-significant correlations with the occurrence of RN were found for male sex (p=0.066) and lung histology of the metastasis (p=0.165). The mean V12Gy was not lower in the RN group compared to the non-RN group, with 37.8 cc and 38.2 cc respectively (p=0.97). V12Gy dichotomised in a <10cc and >10cc group resulted in a p-value of 0.48 in a chi-squared test. Multivariate analysis showed an odds ratio for V12Gy of 1.012 (CI95%= 0.993, 1.031). Other volumes (V5Gy through V20Gy) gave similar results. The gross tumour volume (GTV), conformity index (CI), homogeneity index (HI) did not significantly correlate with the incidence of radionecrosis.

Conclusion We conclude that irradiated healthy brain volume is not associated with the risk of radionecrosis in patients receiving SRT for solitary brain metastases. This is in contrast with previous studies, which have shown a significant increased risk of RN with increasing V10Gy and V12Gy. Although ALARA comes first, our finding may force us to reconsider the role of V12Gy in SRT planning in patients with solitary brain metastases. A V12Gy higher than 10cc did not result in higher risk for RN in patients with single brain metastases. Future studies should analyse whether the prognostic role and suggested thresholds of irradiated brain volumes are dependent on patient specific factors, like number of metastases and type of primary tumour. PO-0905 The impact of adjuvant radiotherapy on molecular prognostic markers in gliomas M. Harat 1 , M. Blok 2 , A. Harat 3 , K. Soszynska 4 1 The Franciszek Lukaszczyk Oncology Center, Radiotherapy, Bydgoszcz, Poland ; 2 bydgoszcz, Poland, ; 3 Public Health, Bydgoszcz, Poland ; 4 10th Military Hospital, Molecular Pathology, Bydgoszcz, Poland Purpose or Objective Changes in MGMT promoter methylation, IDH1 and IDH2 mutation, and 1p/19q co-deletion status in gliomas between first and subsequent resections and their associated clinical factors are poorly described. Here we assayed for these biomarkers in the clinical setting. Material and Methods We used multiplex ligation-dependent probe amplification to measure MGMT promoter methylation, IDH mutation status, and 1p/19q co-deletion in 45 paired tumor samples from patients undergoing resection and subsequent re- resections for gliomas. Results