Departmental Oral Examination (Thesis Title: "Quantitative measurements of Rhenium-188 for radionuclide therapies")

Speaker: 
PEDRO LUIS ESQUINAS FERNANDEZ
Event Date and Time: 
Fri, 2017-03-17 15:00 - 17:00
Location: 
Room 700, Research Pavilion, Vancouver General Hospital - 828 West 10th Avenue
Local Contact: 
Physics and Astronomy, UBC
Intended Audience: 
Public

Abstract:
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 beta-particles, gamma-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 188Re 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 underestimate the true dose by 15-20%, on average.

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