ESTRO 2024 - Abstract Book

S1306

Clinical - Head & neck

ESTRO 2024

1560

Digital Poster

Changes in tumour volume before and during ocular proton beam therapy

Lisa Klaassen 1,2,3 , Christal van de Steeg-Henzen 2,4 , Tina Lengkeek 4 , Geert P. Plug 1,2,5 , Pauline A.C. Bakker 3,4 , T.H. Khanh Vu 1 , Marina Marinkovic 1 , Gregorius P.M. Luyten 1 , Berit M. Verbist 2,4 , Coen R.N. Rasch 3,4 , Jan-Willem M. Beenakker 1,2,3 1 Leiden University Medical Center, Ophthalmology, Leiden, Netherlands. 2 Leiden University Medical Center, Radiology, Leiden, Netherlands. 3 Leiden University Medical Center, Radiation Oncology, Leiden, Netherlands. 4 HollandPTC, HollandPTC, Delft, Netherlands. 5 Inholland, Health, Sports & Wellbeing, Haarlem, Netherlands

Purpose/Objective:

Proton beam therapy is a highly effective treatment option for uveal melanoma, the most common primary intra ocular malignancy in adults, with high local tumour control [1]. However, vision often deteriorates after radiotherapy. Therefore, there is a need for more conformal image-based ocular proton therapy treatment. MRI is increasingly used in ocular oncology and may contribute to 3D image-based therapy planning [2]. Currently, patients have to undergo surgical tantalum clip placement for treatment planning and positioning, requiring general anaesthesia and delaying the treatment. In order to move towards 3D MRI-based clipless ocular proton beam therapy, it is crucial to understand whether and how tumour geometry changes leading up to and during proton beam therapy, as the surgery and/or radiation may result in swelling of the tumour. Therefore, the aim of this study is to evaluate whether tumour volume of uveal melanoma changes during time-to-treatment initiation and proton beam therapy.

Material/Methods:

MRI- scans were performed after surgical clip placement (‘planning MRI’) at the referring hospital (LUMC), and 5 days before the first fraction, and immediately after the final fraction, at the proton therapy center (HollandPTC). All MRI scans were acquired using a dedicated 3 tesla ocular MRI protocol with a surface receive coil (Philips Healthcare, the Netherlands). Tumours were delineated in MevisLab (MeVis Medical Solutions, Germany) on the contrast-enhanced T1-weighted scan with an isotropic acquisition resolution of 0.8 mm and a scan time of 02:06 minutes [3,4]. Tumour volume was determined for all timepoints, as well as tumour prominence (thickness) and clip-tumour distances, which are important metrics in the current model-based treatment planning [5]. Tumour prominence was automatically determined based on the 3D tumour contour, using an earlier described method [6]. The clip-tumour distances were defined as the shortest Euclidean distance between the clip centre and the tumour base.

Results:

Nine patients were included, with a mean tumour thickness of 7.9 mm (range 4.8-12.2 mm) at diagnosis. Four tumours had a juxtapapillary localisation. Time between the planning MRI and the final day of treatment was 19 days on average (range 16-23 days).