Sci‐PM Sat ‐ 06: Investigating dose resolution in CT polymer gel dosimetry

Abstract

X‐ray computed tomography (CT) is a novel method of extracting 3D dose information from irradiated polymer gels and presents an exciting possibility for widespread clinical application of gel dosimetry. However, clinical use remains limited due, in part, to poor dose resolution. This work investigates dose resolution in CT polyacrylamide gel (PAG) dosimetry and provides optimization strategies for improving dose resolution. In addition, using current PAG formulations, achievable dose resolution is calculated for a range of voxel sizes given a 1 hour imaging time constraint. Phantom design, imaging protocol and voxel size are all shown to be important considerations for improving dose resolution due to their effects on image noise. Specific recommendations include: minimizing phantom size, maximizing tube voltage, using standard or soft reconstruction algorithms and increasing voxel size where clinically appropriate. Dose resolution also depends on the sensitivity and dose range of the gel CT to dose response and for PAGs a 50%C (cross‐linking fraction) gel is shown to provide the best dose resolution. With technique optimization dose resolutions of < 3% for region of interest imaging and ∼ 5% for volume imaging (2.5×2.5×3mm3 voxel size) can be obtained. These results approach those of MRI and OCT gel dosimetry within a shorter (⩽ 1hr) imaging time and highlight the potential for CT gel dosimetry to be a clinically successful 3D dosimetry tool. Future work remains in developing gels more sensitive to CT read‐out and implementing multi‐slice CT imaging, advances which stand to further increase the quality of CT gel dosimetry.