ESTRO 2023 - Abstract Book

S806

Monday 15 May 2023

ESTRO 2023

Physiological changes including perfusion, diffusion and metabolite concentration in tumour occur much earlier than morphological changes. These early changes can be used potentially as the biomarkers for therapeutic response prediction. This study aimed to investigate the optimal time for early therapeutic response prediction with multi-parametric MRI in patients with nasopharyngeal carcinoma (NPC) receiving concurrent chemo-radiotherapy (CCRT). Materials and Methods Twenty-seven NPC patients (median age 49, range 26-66) were divided into the responder (N=23) and the poor-responder (N=4) groups by their primary tumour post-treatment shrinkages with more or less than 50% volume respectively. Single voxel proton MR spectroscopy (1H-MRS), diffusion weighted (DW) and dynamic contrast-enhanced (DCE) MRI were scanned with a 1.5T MAGNETOM Aera MR-Simulator (Siemens Healthcare, Erlangen, Germany) at baseline, weekly during CCRT and post-CCRT. The median choline peak in 1H-MRS, the median apparent diffusion coefficient (ADC) in DW-MRI, the median influx rate constant (Ktrans), reflux rate constant (Kep), volume of extravascular-extracellular space per unit volume (Ve); and initial area under the time-intensity curve for the first 60 seconds (iAUC60) in DCE-MRI were compared between the two groups with the Mann-Whitney tests for any significant difference. Results In DW-MRI, the percentage increase in ADC from baseline to week 1 for the responders (median 11.39%, IQR 18.13%) was higher than the poor-responders (median 4.91%, IQR 7.86%) (p=0.027, Figure 1). In DCE-MRI, the iAUC60 on week 2 was found significantly higher in the poor-responders (median 0.398, IQR 0.051) than the responders (median 0.192, IQR 0.111) (p=0.012, Figure 2). No significant difference was found in median choline peaks in 1H-MRS at all time points.

Fig. 1. The median percentage increases in ADC values at different time points. The bottom and top edges of boxes represent the 1st and the 3rd quartiles of values respectively.

Fig. 2. The median iAUC60 at different time points. The bottom and top edges of boxes represent the 1st and the 3rd quartiles of values respectively. Conclusion Early perfusion and diffusion changes occurred in the primary tumours of NPC patients treated with CCRT. The DW-MRI on week 1 and the DCE-MRI on week 2 were the optimal time points for early therapeutic response prediction. MO-0958 corneal surface reconstruction and pupil tracking for eye localization in ocular proton therapy R. Via 1 , G. Fattori 1 , A. Pica 1 , G. Baroni 2 , A. Lomax 1 , D.C. Weber 1 , J. Hrbacek 1 1 Paul Scherrer Institute, Center for Proton Therapy, Villigen, Switzerland; 2 Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria, Milano, Italy Purpose or Objective We present a customised optical system that combines pupil tracking with corneal topography for non-invasive eye localisation. The system performance was compared to the current clinical protocol which makes use of X-ray imaging of tantalum clips sutured to the patient’s eye. In this study, the system was tested for use in MR-based ocular proton therapy, an envisioned non-invasive protocol that uses MRI imaging to create a patient-specific eye model.