PET Quantification for Assessing Tumour Response

Treatment response assessment in advanced head and neck cancer patients using Positron Emission Tomography (PET) has potential to provide significant clinical benefit. PET quantification methods can be either static or dynamic. The static approach is simple and is widely used. The simplified dynamic PET quantification method is a promising approach as it provides a reasonable trade-off between accuracy and clinical practicality. This method requires a blood sample which makes it not ideal since the PET quantification accuracy may be compromised due to small activity and volume of the blood sample. The implementation of image-based simplified dynamic PET quantification in head and neck cancer patients requires partial volume correction due to small vessel sizes and limitted PET spatial resolution. The objective of this thesis is to evaluate the accuracy of current PET quantification methods for response assessment in advanced head and neck cancer patients and to develop a novel and robust partial volume correction technique to improve PET quantification. First, the static PET quantification method using fixed size ROI is evaluated. Significant variation in response assessment was observed suggesting that static PET quantification using a fixed-size ROI should be approached with caution in heterogeneous tumours. Second, the accuracy of blood activity measurements and its effect on the accuracy of quantitative response assessment is evaluated. Significant inaccuracies in the blood sample based simplified dynamic PET quantification method are identified. The results support a need to develop an image-based simplified dynamic PET quantification method with partial volume correction. Finally, a novel partial volume correction technique was developed, validated, and its robustness was investigated. In comparison to previously published partial volume correction techniques, it performed better with noisy PET images and it was more robust for errors in PET-CT registration. The partial volume correction technique was also implemented and validated in sinogram space to provide additional advantages such as applicability to iterative reconstructions. The proposed partial volume correction technique enables the use of image-based simplified dynamic PET quantification in advanced head and neck cancer patients. Furthermore, the technique establishes a framework for future research to address the inherent low spatial resolution of PET.Ph