S2473
Physics - Radiomics, functional and biological imaging, and outcome prediction
ESTRO 2026
experienced readers. References: 1. Perner S, et al. Prostate-specific membrane antigen
expression as a predictor of prostate cancer progression. Human pathology38, 696-701
(2007).2. Hammarsten P, et al. Immunoreactivity for prostate specific antigen and Ki67 differentiates subgroups of prostate cancer related to outcome. Modern Pathology32, 1310-1319 (2019). Keywords: Prostate cancer, Immunoreactivity, PSMA- PET/mpMRI Digital Poster 3856 Temporal correlation between advanced DWI and Ki-67 in patients with skull base chordomas treated with carbon ion radiation therapy Fabio Casaccio 1 , Paolo Fenech 1 , Letizia Morelli 1 , Sara Imparato 2 , Vincenzo Dolcetti 2 , Sara Lillo 3 , Alberto Iannalfi 3 , Ester Orlandi 3 , Guido Baroni 1 , Chiara Paganelli 1 1 DEIB, Politecnico di Milano, Milano, Italy. 2 Radiology Unit, CNAO, Pavia, Italy. 3 Radiotherapy Unit, CNAO, Pavia, Italy Purpose/Objective: Skull base chordomas (SBC) are rare malignant notochordal tumours with marked heterogeneity, hindering the identification of prognostic factors (Duan et al, 2022). Carbon Ion Radiotherapy (CIRT) plays a central role in SBC treatment, and quantitative imaging may help identify prognostic biomarkers to guide and optimize such treatments.In this work, we explore advanced Diffusion Weighted Imaging (DWI) to evaluate changes in the directional diffusion in patients with high ( ≥ 5, KiH) and low ( ≤ 5, KiL) proliferation index (Ki-67) undergoing CIRT. Material/Methods: This study includes 7 patients with SBC treated with CIRT at the National Centre for Oncological Hadrontherapy (CNAO, Pavia, Italy). DWI sequences were acquired with 12 unique diffusion-encoding gradient directions (b- values=[10,20,40,50,60,300,400,1300,1500]s/mm2, TE/ TR=106/3500ms, α =90°) with a 3T scanner equipped with a dedicated Head and Neck coil with 20 channels (Magnetom Skyra FitSiemens), at three time points during CIRT: baseline, 3 months and 12 months follow- up.Pre-processing includes susceptibility- and eddy currents-induced distortions correction (Andersson et al, 2016). After this, maps of Axial (AD) and Radial (RD) Diffusivity were extracted from the multiple DWI directions. First order statistics (i.e., mean, median, standard deviation, interquartile range) were then analysed within the Gross Tumour Volume (GTV) and evaluated across the three time points.
Results: In total, 138 regions were analyzed. The IHC expression of Ki-67 was higher for regions sampled within a GTV (p=0.03). Pair-wise intra-lesion comparison adjusted for Gleason grade revealed that the IHC expression of Ki-67 remained higher in parts of lesions confined to the GTV (p=0.03). Conversely, no such observation was made for the expression of PSMA or tissue PSA. PSMA-PET-positive regions showed higher IHC expression of PSMA (p<0.001). Similarly, this difference remained significant in a pair- wise comparison of regions within the same lesion adjusted for Gleason grade (p=0.003). No corresponding observations were made for regions stratified by visibility on mpMRI. Conclusion: PSMA-PET-positive regions within intraprostatic lesions demonstrated elevated PSMA expression, with no evident differences in expression of Ki-67 or PSA. Ki-67 expression, but not visibility on mpMRI, PSMA expression, or tissue PSA, was higher within the delineated GTV. These observations persisted after adjusting for Gleason grade. These results suggest that the histological heterogeneity within intraprostatic lesions can be partly accounted for by qualitative hybrid imaging interpretation by
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