ESTRO 2021 Abstract Book

S858

ESTRO 2021

Conclusion Our data underline the efficacy of active adjuvant treatment for GBM in overall survival, optimally with RTCT with Stupp protocol, even in an elderly and ECOG > 1 group, without grade III-IV toxicities. As expected, baseline ECOG (before starting local treatment), age and multifocal tumor are the most important prognosis predictor. PO-1030 Homogeneous field radiotherapy in adults meduloblastoma. Report of four cases. I. Paguey Garrido 1 , E. Montero Perea 1 , M. Perucha Ortega 2 , D.M. Muñoz Carmona 1 , P. Romero Pareja 1 1 University Hospital Virgen del Rocío, Department of Radiation Oncology, Seville, Spain; 2 University Hospital Virgen del Rocío, Department of Radiophysics , Seville, Spain Purpose or Objective Medulloblastoma is the most common malignant embryonal tumor of the central nervous system (CNS), arising in the posterior fossa, most commonly in the fourth ventricle with a representation of 3% in adults. This disease typically spreads through the cerebrospinal fluid (CSF) within the central nervous system. The standard treatment consists of maximal surgical resection followed by radiation therapy which includes the whole craniospinal axis followed by a boost in the posterior fossa and chemotherapy. The goal of craniospinal irradiation (CSI) is to treat all spaces where cerebrospinal fluid dissemination can result in tumor deposits. This includes the entire sub-arachnoid space from the vertex to the bottom of the thecal sac and includes the spinal nerve roots laterally. One of the issues under discussion is the delineation within the clinical target volume (CTV) of the CSF space around the cribriform plate because some authors claime that that sufficient dose coverage of the whole central nervous system, including the cribriform plate, is essential in preventing recurrence of the disease in this place. Materials and Methods We review a treatment plannning for 4 patients who had been treated for medulloblastoma grade IV, at our hospital, in the time period 2019 to 2020 with tomotherapy CSI. In total, 1 patient was a child (2 to 17 years), 1 patient was a young adult (18 to 30 years), and 2 patient were adults (30 to 60 years) of whom 100% were male. The prescribed dose was 36Gy except for the child who was 23.4Gy. All delimitation plans included the cribiform plate in the CTV. We took as a reference a holocranial dose point which was located close to the pituitary gland. Results The dose (Gy) received in the cribriform plate and in the reference holocranial dose point were 35,07 vs 35,92; 36,39 vs 37,58; 36,46 vs 36,9; 23,65 vs 23,81, respectively. The average dose received by the cribriform plate was 100.65% . 3 patients were alive and no patient had suffered a recurrence. The fourth patient died of a cause unrelated to the tumour process. Conclusion In line with the current trend, we observe that we comply with sufficient dose coverage in the cribriform lamina. After carefully reviewing the literature on relapse in medulloblastoma, we found that the occurrence of frontobasal meningeal relapses are a known phenomenon in childhood medulloblastomas even years after treatment and have been correlated as a possible predisposing factor with insufficient radiation and with position during surgery. However, we did not find a particular trend of frontobasal relapse in adults in the literature. Therefore, the need to include the cribriform plate in CSI should be investigated as it is associated with increased side effects and potential second tumours. PO-1031 Tumour volume influences local control and overall survival following Stereotactic Radiosurgery S. Lynch 1 , M. Varasteh 2 , E. Russell 2 , J. Harney 1 , D. Conkey 1 , A. Cole 1 , S. Osman 2 , T. Flannery 3 , K. Prise 2 , A. O'Neill 1 , C. McGarry 1,2 1 Belfast Health and Social Care Trust, Clinical Oncology, Northern Ireland Cancer Centre, Belfast, United Kingdom; 2 Queen's University Belfast, Patrick G Johnston Centre for Cancer Research, Belfast, United Kingdom; 3 Belfast Health and Social Care Trust, Neurosurgery, Belfast, United Kingdom

Purpose or Objective Stereotactic radiosurgery (SRS) is increasingly used in preference of whole brain radiotherapy (WBRT) for