ESTRO 2022 - Abstract Book

S988

Abstract book

ESTRO 2022

PO-1165 Pattern of recurrence of glioblastoma treated with non-coplanar volumetric modulated arc therapy

I. Georgiou 1 , P. Bhatt 2 , P. Bodkin 2 , A. Giamouriadis 2 , S. Ross 2 , J. Walkden 2 , S. Olson 3 , A. Neelakantan 3 , A. Torgersen 4 , M. Whibley 1 , R. Moleron 1 1 Aberdeen Royal Infirmary, Department of Oncology, Aberdeen, United Kingdom; 2 Aberdeen Royal Infirmary, Department of Neurosurgery, Aberdeen, United Kingdom; 3 Aberdeen Royal Infirmary, Department of Radiology, Aberdeen, United Kingdom; 4 Western General Hospital, Neuropathology Unit, Department of Pathology, Edinburgh, United Kingdom 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. Materials 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. R. Madan 1 , S. Dhayalan 1 , A.S. Oinam 1 , P. Tomar 1 , N. Kumar 1 , S. Goyal 1 , D. Khosla 1 , K. Periasamy 1 , S.K. Sahoo 2 , C.K. Ahuja 3 , D. Chatterjee 1 1 Postgraduate Institute of Medical Education and Research, Radiotherapy and Oncology, Chandigarh, India; 2 Postgraduate Institute of Medical Education and Research, Neurosurgery, Chandigarh, India; 3 Postgraduate Institute of Medical Education and Research, Radiodiagnosis and Imaging, Chandigarh, India Purpose or Objective Craniospinal irradiation (CSI) is an integral component of multimodality management in medulloblastoma (MB). Hematological toxicity is one of the commonest toxicity observed during CSI leading to treatment breaks and increased overall treatment time. Arc based RT techniques i.e. VMAT expose large volume of normal tissue to low RT dose, which might increase the risk of bone marrow toxicity. The aim of the current study is to compare the incidence of hematological toxicity in 3DCRT and VMAT technique. Materials and Methods The study was conducted in the department of radiotherapy and oncology, over a period of 18 months. MB patients who received CSI during the said period were analysed. All patients were treated in the supine position on a 6 or 15 MV linac. 3DCRT was the most commonly employed technique. VMAT was used only if homogeneity or dosimetric constraints were not achieved. In 3DCRT technique, 2 lateral fields were used for cranial field, matched to the spinal field by collimation and couch rotation. VMAT was planned by 4-6 full arcs using 2-3 isocentres. Complete blood counts were checked twice weekly during CSI. Details of patients experiencing toxicity and treatment gap were documented in Microsoft Excel sheet. SPSS v 23 was used for statistical analysis. PO-1166 Impact of radiation techniques on hematological toxicity during craniospinal irradiation

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