Computational and experimental methods for imaging and dosimetry in 177Lu radionuclide therapy : Classical and novel gamma cameras

Sammanfattning: Radionuclide therapy (RNT) is a form of radiotherapy that uses unsealed radioactive sources for the delivery of ionising radiation within a patient's body.Radiation dosimetry is not used routinely in all centres, and the RNT field can benefit from more data on pharmacokinetics and absorbed doses (ADs).Consequently, there is a value in developing and investigating methods that facilitates the acquirement of pharmacokinetic data and AD calculation.Papers I and IV focus on tumour dosimetry in peptide receptor radionuclide therapy (PRRT) with [177Lu]Lu-DOTA-TATE. In Paper I, a method for tumour dosimetry was developed, with the intention to be applicable to image sets consisting of a combination of planar and single photon emission computed tomography (SPECT) images. Semi-automatic segmentation methods are developed and employed for robustness and to alleviate the operator workload. Evaluation showed that the dosimetry method worked well provided that tumour selection criteria were applied. In Paper IV, this method was applied across all treatment cycles in a larger set of patients, producing a large collection of ADs and pharmacokinetics data for tumours. Analysis showed how the ADs evolved over treatment cycles and how this could be explained by changes in the pharmacokinetic parameters, findings which in the long run could help in the design of new treatment and imaging protocols.Papers II, III and V focus on a cadmium zinc telluride (CZT)-based hand-held gamma camera and lay the groundwork for its application within RNT. In Paper II, the camera was characterised and the feasibility of using it for 177Lu imaging was investigated. We found that it was capable of producing useful images and identified appropriate collimators and energy windows. In Paper III, we sought to improve the understanding of how the energy-tailing associated with the CZT-crystal affected 177Lu imaging with the help of Monte Carlo simulations. The wide range of energies of interest for 177Lu meant that new model of the camera system had to be developed and tuned to reproduce the camera's behaviour. Through the model, we were able to gain a better understanding of the camera and estimate the interference of higher-energy photons on lower energy windows. In Paper V, we aimed to develop a method with which the camera could be used for activity quantification. This was done by adapting a dual-photopeak method to 177Lu, a method in which measurements over multiple photopeaks are employed to infer the depth of a source, allowing for activity-quantification with attenuation-correction.