ESTRO 2024 - Abstract Book

S3917

Physics - Image acquisition and processing

ESTRO 2024

1 Radiation Physics, Department of Hematology, Oncology, and Radiation Physics, Skåne University Hospital, Lund, Sweden. 2 Department of Translational Medicine, Medical Radiation Physics, Lund University, Malmö, Sweden. 3 Division of Oncology, Department of Clinical Sciences Lund, Skåne University Hospital, Lund, Sweden

Purpose/Objective:

Fiducial markers have been widely utilized in image-guided radiotherapy for prostate cancer treatment [1-3]. The purpose of fiducial markers is to minimize the geometric uncertainty during the daily setup of patients and variations in target position [3]. Diffusion magnetic resonance imaging (dMRI) for target delineation has potential for precise localization of malignant foci in the prostate, enabling intraprostatic focal boost [4-6]. Furthermore, studies have shown that the apparent diffusion coefficient (ADC) map can be used for monitoring and as an indicator for follow-up in prostate cancer treatment [7-8]. The presence of metal fiducial markers introduces changes in the static magnetic field, due to the difference in susceptibility between the metal and the surrounding tissues [9]. The standard acquisition technique for dMRI is echo planar imaging (EPI). However, it is sensitive to local field variations, and the resultant geometrical distortion artefacts and signal loss become more pronounced compared to T1-weighted (T1W) or T2-weighted (T2W) imaging using spin echo or gradient echo-based acquisition techniques [10]. Therefore, the impact of the image artefacts from fiducial markers should be investigated on prostate dMRI as it could be detrimental for target delineation.

The aim of this study is to determine the radial margin from the center of the fiducial markers to the voxel that is not affected by the artefact in dMRI-images and ADC-maps using a quantitative analysis method.

Material/Methods:

A gelatin nickel-nitrate phantom with three fiducial markers (1x5 mm), placed in perpendicular directions, was utilized (Fig. 1A). This enabled depiction of artefacts in phase- (PE), frequency- (FE) and slice-encoding direction (SE) with respect to the marker position. T1W-, dMRI (b = 0, 200, 800, 1000 mm²/s) and ADC-images were obtained from a 3T GE Healthcare system (Software SIGNA_LX1.MR30.0_R01_2242.a, General Electric Healthcare, Milwaukee, WI, USA).