Masteruppsatser / Medicinsk strålningsvetenskap

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Browsing Masteruppsatser / Medicinsk strålningsvetenskap by Author "Becker, Vanessa"

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    Optimization of Kidney Dosimetry: Determination of Recovery Coefficient for Kidneys and SPECT/CT Imaging of [177Lu]Lu-DOTATATE/TOC
    (2025-10-06) Becker, Vanessa; University of Gothenburg/Institute of Clinical Sciences; Göteborgs universitet/Institutionen för kliniska vetenskaper
    Purpose: Peptide receptor radionuclide therapy (PRRT) with [177Lu]Lu-DOTATATE/TOC is an effective treatment for neuroendocrine tumors, but this treatment also involves an unwanted radiation dose to the kidneys. Dosimetry can be used to optimize treatment and reduce kidney toxicity, and therefore, obtaining an accurate estimate of activity concentration in the kidneys is essential. One of the main challenges in quantitative SPECT imaging for dosimetry is the partial volume effect, which leads to an underestimation of activity. This effect can be corrected for by using a recovery coefficient (RC). The study aimed to obtain an RC for kidneys using a software developed by Hermes for organ and tumor dosimetry. The study investigates how the RC is affected by different activity concentrations in the kidneys and the ratio between the activity concentration in the kidney and the background. It was also studied how the RC is affected by different reconstruction methods and two different projection sets, 30 and 60 projections. Method: Five 3D-printed kidney phantoms were filled with [177Lu]Lu-DOTATATE/TOC and placed in either a Jaszczak phantom or a NEMA phantom. Different activity concentrations were investigated as well as different ratios between the activity concentration in the kidney and the background. Images were collected with a SPECT/CT system (GE Healthcare Discovery NM/CT 670 Pro) and reconstructed in Hermes (Hermia Hybrid Recon 5.0.) using Ordered Subset Expectation Maximization (OSEM) and Relative Difference Prior (RDP). The kidneys were manually segmented, and the RC was determined for each measurement. In addition, the RC was compared between different segmentation methods i.e. the whole kidney segmented volume of interest (VOI), and the small VOI method was examined. Results: The RC was not statistically significantly affected by variations in activity concentration or kidney-to-background ratios. However, a statistically significant difference was shown between the two reconstruction methods, where reconstruction using RDP resulted in a higher RC than when reconstructing images with OSEM. A statistically significant difference was also found between 30 and 60 projections, probably due to increased noise in 30 projections. When comparing various activity concentrations, the whole kidney segmentation approach’s standard deviation was smaller than that of the small VOIs method. At Sahlgrenska University Hospital, the RC was determined to be 0.80 with whole kidney segmentation, 60 projections collected and reconstructed with RDP. Conclusion: The RC for kidneys in SPECT/CT imaging with [177Lu]Lu-DOTATATE/TOC are stable across the investigated range of activity concentrations and background ratios, supporting the use of a standardized RC for all imaging time points for whole kidney segmentation in dosimetry. At Sahlgrenska University Hospital, the RC was determined to be 0.80 and the method for determination of the RC is considered reasonable.