UBC Theses and Dissertations
Patient-specific internal dose calculation techniques for clinical use in targeted radionuclide therapy Grimes, Joshua
The objective of this thesis was to investigate and develop a set of methods for accurate dose calculation that would be practical to implement into routine clinical use. Towards this aim, a graphical user interface (GUI) was developed in order to handle the large body of data associated with internal dose calculations and to perform each step in the dose calculation procedure. Furthermore, an iterative adaptive thresholding method for determining volumes and activities of objects in single photon emission computed tomography images was developed and the accuracy and reproducibility of this method was investigated. Next, organ level and voxel S value dose calculations were compared to results from Monte Carlo simulation. This comparison included the assessment of various aspects of OLINDA/EXM dose calculation such as the use of stylized reference phantoms used to represent the average patient and the sphere model used to estimate tumour dose. Finally, the internal dosimetry techniques investigated in this thesis were applied to estimate patient-specific absorbed doses in patients imaged for suspected neuroendocrine tumours and in patients treated with ¹⁸⁸Re microspheres. The proposed iterative adaptive thresholding method was found to accurately and reproducibly determine object volumes and activities in phantom and patient studies, regardless of the image reconstruction method used. In the comparison of OLINDA/EXM to Monte Carlo dose calculations, variation in patient-specific anatomy was found to lead to large differences between cross-organ dose estimates based on stylized phantoms in OLINDA and corresponding cross-organ dose estimates calculated for each patient with Monte Carlo. However, total organ doses agreed within 6%. Monte Carlo and voxel S value dose calculations were found to produce nearly identical 3-dimensional dose distributions within source organs. Analysis of the patients scanned for neuroendocrine tumours revealed large dose variations in tumours and normal organs between patients. The ratio of tumour-to-kidney dose ranged from 0.13 to 2.9, demonstrating the importance of determining patient-specific dose estimates. Finally, response data in the patients treated with ¹⁸⁸Re microspheres did not correlate with mean or maximum tumour dose, but it was found to correlate with the minimum dose received by 90% of the tumour volume (D90).
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