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UBC Theses and Dissertations

Quantitative measurements of Rhenium-188 for radionuclide therapies Esquinas Fernández, Pedro Luis


Over the last three decades, Rhenium-188 (¹⁸⁸Re) applications in Nuclear Medicine therapies have gathered a lot of interest thanks to the favorable physical and chemical characteristics of this isotope. In order to optimize ¹⁸⁸Re therapies, the accurate knowledge of the activity distribution within the patient body is required. To this end, the nuclear medicine images must yield accurate quantitative measurements. However, the decay of ¹⁸⁸Re results in a large variety of emissions such as β-particles, γ-particles and Bremsstrahlung, making quantitative measurements of ¹⁸⁸Re activity a very difficult task. The objective of this thesis was to develop a series of methods which would allow us to perform accurate measurements of ¹⁸⁸Re activities in the nuclear medicine department. To address the thesis’ objective, four major studies were carried out: 1) to ensure that measurements of patients administered activities are accurate, a practical method to determine dose-calibrator dial settings using a thyroid-probe was developed; 2) to assess the influence of ¹⁸⁸Re multiple emissions on quantitative imaging, a series of Monte-Carlo simulations of ¹⁸⁸Re single photon emission computed tomography (SPECT) were performed; 3) to assess the image quality and image quantification accuracy of a pre-clinical SPECT camera based on multi-pinhole collimators, a series of experiments using phantoms filled with ¹⁸⁸Re were performed and; 4) to investigate the accuracy of quantitative ¹⁸⁸Re SPECT using a clinical system as well as the accuracy of image-based dosimetry calculations in the context of ¹⁸⁸Re radioembolization, a series of phantom experiments and Monte-Carlo simulations were performed. The proposed thyroid-probe method enabled us to determine dose-calibrator settings for ¹⁸⁸Re which resulted in measurements of activity within 5% of the sample’s true value. The analysis of Monte-Carlo simulations indicated that Bremsstrahlung photons emitted from ¹⁸⁸Re do not really affect image-quantification. The results from phantom experiments showed that accurate quantification of Re-188 activities is possible in pre-clinical and clinical SPECT when images are reconstructed with iterative algorithms and corrections for attenuation, scatter using the triple-energy window method, resolution loss and dead-time. Due to the sub-optimal segmentation methods, dosimetry calculations based on ¹⁸⁸Re images underestimated the true dose by 15-20%, on average.

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