Inter-observer variation in target delineation and dose trade-off for radiotherapy of paediatric ependymoma

Postoperative radiotherapy for intracranial paediatric ependymoma is challenging both for target definition and treatment planning [1]. Delineation of the tumour bed is difficult, as structures in prior contact with the tumour will shift back into their original positions after surgery. In infratentorial cases, the target is adjacent to the brainstem and upper spinal cord, therefore the relatively high prescription dose and sparing of surrounding organs at risk (OARs) need to be balanced. Through the radiotherapy working-group of the Nordic Organization of Pediatric Hematology and Oncology (NOPHO) and in collaboration with the Westdeutsches Protonentherapizentrum Essen (WPE), a study was performed to quantify inter-centre variations in target delineation and treatment plans for these tumours