Pattern of recurrence of glioblastoma treated with non-coplanar volumetric modulated arc therapy
Rafael Moleron,
United Kingdom
PO-1165
Abstract
Pattern of recurrence of glioblastoma treated with non-coplanar volumetric modulated arc therapy
Authors: Ioannis Georgiou1, Pragnesh Bhatt2, Peter Bodkin2, Anastasios Giamouriadis2, Sheila Ross2, James Walkden2, Shona Olson3, Asha Neelakantan3, Antonia Torgersen4, Margaret Whibley1, Rafael Moleron1
1Aberdeen Royal Infirmary, Department of Oncology, Aberdeen, United Kingdom; 2Aberdeen Royal Infirmary, Department of Neurosurgery, Aberdeen, United Kingdom; 3Aberdeen Royal Infirmary, Department of Radiology, Aberdeen, United Kingdom; 4Western General Hospital, Neuropathology Unit, Department of Pathology, Edinburgh, United Kingdom
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Purpose or Objective
A 2cm margin is typically added to the gross tumour volume in the delineation of clinical target volume (CTV) for the treatment of glioblastoma as most recurrences occur locally. Non coplanar VMAT increases the conformity of the radiotherapy treatment so intermediate doses delivered to non-target volumes are decreased. The potential impact in the pattern of recurrence is explored in this study.
Material and Methods
111 patients with histologically confirmed glioblastoma were included in this retrospective single institution study, which were all treated with non-coplanar VMAT radiotherapy between 2014 and 2020. Pre and postoperative MRIs and at the time of progression were compared. Twenty-six (23.5%) had undergone >90% resection, 35 (31.5%) 50-89% resection, 19 (17.1%) <50% resection, 24 (21.6%) a biopsy and 7 patients (6.3%) had unknown extent of resection. Eighty-one (73.0%) received 60Gy in 30 fractions and 30 (27.0%) received 40Gy in 15 fractions. 94 (79,0%) received concurrent and adjuvant temozolomide.
Results
Median progression free survival (interquartile range) was 6.3 (5.0,11.8) months. Median overall survival (IQR) was 13.8 (6.8,23.4) months. O6-methylguanine-DNA methyltransferase (MGMT) promoter was methylated in 50.5% of the patients. Isocitrate dehydrogenase 1 (IDH1) mutations were present in 9.0% of the patients. Seventy-four (66.7%) of the patients presented with local recurrence, 11 (9.9%) with distal recurrence (>2cm from previous enhancing lesion), 2 (1.8%) with spinal dissemination and 12 patients (10.8%) had no progression on follow-up scans. Twelve patients (10.8%) died prior to receiving a scan with signs of progression. Binary logistic model showed no statistical association between extent of resection, radiotherapy dose, addition of chemotherapy, MGMT methylation or IDH1 mutations with the differential pattern of recurrence in this series.
Conclusion
Despite the increase in conformality achieved with non-coplanar VMAT radiotherapy, local recurrence within the CTV is the most common pattern of recurrence. This pattern is independent of biological and treatment related factors.