ESTRO 2025 - Abstract Book

S1617

Clinical – äediatric tumours

ESTRO 2025

976

Proffered Paper Cyst dynamics in children with craniopharyngioma during radiotherapy Fatma Sen 1 , Sabine Frisch 1 , Martin Bischoff 1 , Rolf-Dieter Kortmann 2 , Sarah Peters 1 , Dalia Ahmad Khalil 1 , Benjamin Koska 3 , Hermann L. Müller 4 , Carsten Friedrich 4 , Beate Timmermann 1,5 1 Department of Particle Therapy, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), University Hospital Essen, Essen, Germany. 2 Department of Radiation Oncology, University of Leipzig, Leipzig, Germany. 3 West German Proton Therapy Centre Essen (WPE), University Hospital Essen, Essen, Germany. 4 Department of Paediatrics and Paediatric Haematology/Oncology, University Children’s Hospital, Carl von Ossietzky University Oldenburg, Klinikum Oldenburg AöR, Oldenburg, Germany. 5 German Cancer Consortium (DKTK), Essen/Düsseldorf, University Medicine Essen, Essen, Germany Purpose/Objective: Craniopharyngiomas (CP) are rare, slow-growing brain tumors that often contain cystic components in pediatric patients. Changes of these cysts can significantly affect radiotherapy (RT) as adequate target coverage cannot be ensured requiring re-planning. Therefore, repetitive imaging control is needed. This study reports on cyst dynamics during RT. Material/Methods: This retrospective study obtained ethical approval (23-11199-BO) from local Ethics Committee, while data were drawn from the registry KiProReg (DRKS00005363). Children with cystic CP treated with proton beam therapy between 2015-2023 were analyzed. Repetitive images of patients with at least two verification MRI during RT were assessed. Cyst volume of the planning MRI and of the MRI with the maximum cyst volume during RT was analyzed using a 3D planning software (RayStation®). The number of re-plans was evaluated. For follow-up (FU) evaluation, progressive disease (PD) was defined according to RAPNO criteria. Other cyst enlargements were considered as temporary non-PD growth. Results: 52 patients (median age at diagnosis 7.8 years (range, 3.0-17.1 years), f/m 25/27) with a median of three verification MRIs per patient (range, 2-6 MRI) during RT were analyzed. Cyst components were single (50%) and multiple (50%), respectively. The median cyst volume was 1.2 cm³ (range, 0.1-21.5 cm³) at RT planning and 1.5 cm³ (range, 0.3-22.4 cm³) during RT. Due to cyst dynamics, plans of 11 children (21%) needed 1-2 plan adjustments during RT after a median of 17 days (range, 2-35 days). These 11 patients had a cyst growth from a median of 3.0 cm³ (range, 0.1-19.8 cm³) before to 4.3 cm³ (range, 1.0-22.4 cm³) during RT. Of them, seven children presented with multiple cystic components and three required a second re-plan. Median FU time after RT was 1.9 years (range 0.0-6.1 years). Two patients experienced local PD (solid n=1, cystic n=1). These two patients had not required any re-plan during RT. Temporary non-PD cyst enlargement during FU was observed in 15 patients. Of them, one had received re-planning during RT. The following MRI of these 15 patients showed a cyst volume decrease in nine, no decrease in two patients, while there were no following MRIs available in four patients. Conclusion: Cystic changes requiring adjustment of RT plans occurred in about 20% of our patients. Therefore, we can confirm that patients with cystic CP need routine surveillance imaging every other week during RT. Patients with rapid growth of cystic components may need even more frequent monitoring.

Keywords: craniopharyngioma, radiotherapy, cyst