ESTRO 2023 - Abstract Book

S434

Sunday 14 May 2023

ESTRO 2023

Materials and Methods Our data included patients (pts) treated via the proton overseas programme in Jacksonville, Florida between 2010 – 2018, before a National Health Service PBT service became available in the UK. Pts were included if they had received >60 Gy(RBE) PBT for BoS chordomas/chondrosarcomas and had ≥ 12 months follow-up data. Following the parameters identified by the Schröder model, data were collected on total dose received, age at treatment, hypertension, D1cc left and right temporal lobes and presence/absence of CTCAE grade (G) ≥ 2 TRN. We calculated the patient-wise predicted NTCP using the formula in the Schröder paper. Results A total of 93 pts were identified. Median age 48 years (range 7-77), median total dose received 73.8 Gy(RBE) (range 66 – 75.6). After a median follow up of 46 months (range 12 – 122), 8 pts (9%) developed G ≥ 2 TRN. In 2 pts, the grade of TRN could not be ascertained from the notes and was described as unknown. The box plots of predicted patient-wise NTCP vs G ≥ 2 TRN presence (figure 1) indicate good model discrimination. Patient-wise predicted NTCP values gave an AUC-ROC of 0.80, with a dichotomic threshold NTCP=0.2 optimising specificity (78%) and sensitivity (75%) (figure 2). Pts who went on to develop G ≥ 2 TRN had a median predicted probability according to the Schröder model of developing toxicity of 29% (interquartile range 19-40%) versus 11% (interquartile range 6-18%) in those without G ≥ 2 TRN.

Conclusion Our results show a comparable high AUC-ROC value as in the Schröder paper, demonstrating that the model has a good predictive ability for TRN development. The predicted patient-wise NTCP of 0.2 could be suggested as a cut off, above which pts are at increased risk of developing TRN, however further work is required to develop a practical clinical tool. Reference [1] Schröder et al. NTCP Modeling for High-Grade Temporal Radionecroses in a Large Cohort of Patients Receiving Pencil Beam Scanning Proton Therapy for Skull Base and Head and Neck Tumors.Int J Radiat Oncol Biol Phys 2022:1–8. MO-0555 Novel target volume delineation method in glioblastoma I. Popp 1 , M. Bulach 1 , A. Bilger 1 , E. Gkika 1 , A. Grosu 1,2 1 Medical Center - University of Freiburg, Department of Radiation Oncology, Freiburg, Germany; 2 German Cancer Consortium (DKTK), Partner Site Freiburg, Freiburg, Germany Purpose or Objective For target volume delineation in glioblastoma there are currently two major consensus guidelines being used, the one of the European Organization for Research and Treatment of Cancer (EORTC) and the one of the Radiation Therapy Oncology