ESTRO 2020 Abstract book

S310 ESTRO 2020

Karnofsky performance status, number of BMs, presence of extracranial metastases and tumour genotype. The SES is represented by a score, based on education level, income and employment, and is determined periodically by the Netherlands Institute for Social Research. The scores are published as averages per postal code. The individual SES scores used in analysis were those most current at baseline. A log-rank test was used to compare SES quartiles. Cox proportional hazard models were made for each tumour group, as well as for the cohort as a whole. Included were the SES score, together with the prognostic factors from the GPA. Results In total, 401 patients were included. Median follow-up was 9.6 months, and 345 deaths were observed. The SES score in this cohort ranged from -2.69 to 2.62, with a mean and standard deviation comparable to that of the general population (0.41 and 0.91, respectively). Baseline characteristics per SES quartile are shown in Table 1. Individual adjusted hazard ratios for SES per primary tumour are shown in Figure 1, along with the HR for the entire cohort. The HR for SES in all tumour types is 1.00 (95% CI 0.89-1.13). Similar HRs are seen in NSCLC and GI, with broader confidence intervals for the smallest subgroups, with the one in the RCC group not including 0. However, in the full model an interaction between SES and tumour type was not significant, suggesting the prognostic effect of SES is not dependent on the primary tumour. Unadjusted Kaplan-Meier survival curves are shown in Figure 2, showing largely comparable survival across the SES quartiles during the first months of follow-up. After 20 months the curves start to deviate. However, the log-rank test found no significant difference.

Conclusion After adjusting for prognostic factors from the GPA, SES has no independent prognostic value for survival in the full cohort of patients with brain metastases undergoing radiation therapy. No robust prognostic value of SES was seen in any of the tumour-based subgroups either, although an effect in patients with a RCC cannot be excluded. This leads us to conclude that SES does not impact survival in this cohort.

Poster Highlights: Poster highlights 18 PH: MRI guidance

PH-0527 The design of an MR-PET for radiotherapy treatment simulation. The search for small tumour volumes J. Lagendijk 1 , C. Beijst 2 , B. Woutjan 2 , H. Erik 2 , S. Bart 2 , A. Cezar 2 , W. Bjoern 3 , S. David 3 , G. Pierre 3 , G. Nicolas 3 , D. Thomas 3 , B. Martino 4 , M. Jurgen 5 , S. Volkmar 3 , S. Andre 5 , L. Oliver 5 , V.D.M. Peter 5 , V. Marc 5 , D.J. Hugo 2 , K. Dennis 2 1 UMC Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands ; 2 UMC Utrecht, Department of Radiology, Utrecht, The Netherlands ; 3 Rheinisch- Westfaelische Technische Hochschule, Radiology, Aachen, Germany ; 4 Futura Composites, Development, Heerhoguwaard, The Netherlands ; 5 Philips Medical Systems, Development, Best, The Netherlands Purpose or Objective The Unity 1.5T MR-linac is able to provide stereotactic precision for every (moving) location in the body. This potential to steer the dose at sub-mm scale stresses the need for accurate multi-functional imaging for target definition. An integrated 1.5T MR-PET simultaneously provides excellent anatomical localization of the PET signal, due to the intrinsic registration between both modalities. The 1.5T MR could also provide the same real-time imaging of