ESTRO 38 Abstract book

S388 ESTRO 38

PO-0756 Evaluating the DS-GPA in patients with 1-10 brain metastases treated with stereotactic radiosurgery S. Nagtegaal 1 , A. Claes 1 , T. Snijders 2 , J. Verhoeff 1 1 UMC Utrecht, Radiation Oncology, Utrecht, The Netherlands ; 2 UMC Utrecht, Neurology, Utrecht, The Netherlands Purpose or Objective There are multiple prognostic models for predicting survival after treatment for brain metastases. One of them, the diagnosis-specific Graded Prognostic Assessment (DS-GPA), has been developed to predict the median survival for brain metastases from the most frequent primary sites. Our objective is to compare the survival predicted by the DS-GPA to actual survival in patients treated with SRS for 1-10 brain metastases. We will both evaluate the ability of the DS-GPA to predict the survival on an individual level, as well as its success in dividing a group of patients into different prognostic strata. Material and Methods We identified a consecutive cohort of patients treated with SRS for brain metastases in our institute. DS-GPA scores were calculated for each patient, and the median survival for each DS-GPA group was calculated. Differences in survival between DS-GPA groups were tested with Kaplan-Meier curves. Results Out of a total of 401 patients treated with SRS from 2012- 2017, 366 patients with calculable DS-GPA were identified. Waterfall plots showing the difference between predicted median and actual survival per patient are shown in Figure 1, stratified by the number of brain metastases. The proportion of the survival times within each predicted quartile was 26.6%, 30.7%, 24.9% and 17.8% (for Q1-Q4, respectively). Figure 2 shows the Kaplan-Meier curves of the disease groups with a statistically significant difference between the DS-GPA strata.

Conclusion DS-GPA seems to be a reliable tool for brain metastases patients treated with SRS. Although the differences between the predicted median and the actual survival difference can be large, the distribution of the actual survival within the predicted quartiles is as expected. This means that, although the DS-GPA doesn’t give a point prediction of survival, it is able to accurately predict the range in which the survival will fall. Furthermore, the DS-GPA is also useful in dividing the renal cell carcinoma, melanoma and both NSCLC disease groups into strata with different survival. This allows physicians to place a patient in a certain prognostic group, which may help to determine the most optimal treatment and the duration and frequency of follow-up. The way physicians and other health professionals discuss the results of the DS-GPA score is important. The fact that it results in a median survival and not a point-predicted survival is an important distinction. Patients should not be told that the DS-GPA gives a precise prediction of the expected survival. Instead, a patient needs to be told that around half of the patients with similar clinical characteristics reach the median age, but that the other half dies before that time. This corresponds with our findings. Additionally, the window of survival that applies to half of the patients, i.e. the interquartile range, is another important message for patients, which is also something we have found in this study. PO-0757 Radiosurgery for cranial and spinal haemangioblastomas: monoinstitutional analysis. V. Pinzi 1 , A. Viola 2 , E. De Martin 3 , C. Iezzoni 4 , M. Cerniauskaite 1 , M. Marchetti 1 , L. Fariselli 1 1 Fondazione IRCCS Istituto Neurologico C. Besta, Neurosurgery- Unit of Radiotherapy, Milan, Italy ; 2 University of Milan, Radiation Oncology, Milan, Italy ; 3 Fondazione IRCCS Istituto neurologico C. Besta, Health Department, Milan, Italy ; 4 Fondazione IRCCS Istituto Neurologico C. Besta, Neurosurgery-Radiotherapy Unit, Milan, Italy Purpose or Objective Hemangioblastomas (HB) of the central nervous system are rare indolent WHO grade I vascular tumors of controversial origin that may occur sporadically or in association with von Hippel–Lindau (VHL) disease. Though primary therapy for HB is surgical resection, for patients