Medical Physics Seminar – Monday, February 27, 2023
Cyclotron production of radioscandium from enriched calcium targets for cancer imaging applications
Graduate Research Student
Targeted radionuclide therapy (TRT) is a growing approach to treating cancer, particularly in metastatic disease and other types of cancer not suited to traditional radiotherapy. Several therapeutic radionuclides for TRT, including 225Ac and 177Lu, lack a positron-emitting analogue of the same element to be used for the diagnostic scans. Thus, many investigators have been using the well-established PET radionuclide 68Ga (t1/2 = 67.71 m, Î²+mean = 829.5 keV) as an imaging analogue. However, 68Ga's short half-life presents limitations when considering long time point imaging and transportation to nearby clinics while it's high mean positron energy results in poor PET image resolution.
There are two positron-emitting radioisotopes of scandium: 43Sc (t1/2 = 3.891 h, Î²+mean = 476 keV) and 44gSc (t1/2 = 3.97 h, Î²+mean = 632 keV). 43Sc and 44gSc's roughly four-hour half-life allow for biodistribution images > 4 hours post-injection and may be transported to nearby clinics without a cyclotron on-site. Both 43/44gSc exist primarily in the +3 oxidation state similar to therapeutic isotopes such as 177Lu and 161Tb. The chemical similarity of scandium to light lanthanides suggests that scandium-labeled agents may have comparable biodistributions to the same agents labelled with 177Lu or 161Tb. In addition to acting as an imaging analogue to radioisotopes of other elements, 43/44gSc can be used with the therapeutic radioisotope of scandium, 47Sc, presenting the opportunity to develop a theranostic pair of the same element. This work explores cyclotron production methods for 43/44gSc and investigates 43Sc's and 44gSc's potential in-vitro and in-vivo for cancer imaging applications.
Advanced X-ray Imaging Techniques for Hepatic Arterial Blood Velocity Measurement
Joseph F. Whitehead
Graduate Research Assistant
Embolization is the standard of care for intermediate-stage hepatocellular carcinoma which accounts for 85-90% of primary liver cancers. During this procedure, microspheres are injected into tumor feeding arteries with the goal of reducing blood flow to cancerous regions and inducing tumor necrosis. Treatment endpoints currently rely on subjective, visual assessment using digital subtraction angiography (DSA). Due to this subjective analysis, the decrease in blood flow achieved during embolization has high interobserver variability, which is important since treatments ending within a 'Goldilocks' zone of flow reduction have been shown to increase overall survival. Quantitative digital subtraction angiography (qDSA) aims to standardize treatment endpoints for embolization procedures by measuring arterial blood velocity intra-procedurally from time-resolved, 2D x-ray angiograms, acquired at 30 frames/s DSA imaging. Clinically, DSA imaging is performed at 3-5 frames/s.
Therefore, to improve clinical translatability of qDSA, there is a need to reduce radiation dose. Furthermore, the qDSA approach is also sensitive to vessel motion. To this end, the purpose of this work was then to 1) develop and evaluate a motion-compensated qDSA approach and 2) reduce radiation dose by using a novel interleaved angiography technique. This new technique provides high frame rate, lower radiation dose images for blood velocity quantification while simultaneously providing higher dose images at the same frame rate as conventional DSA for visualizing vessel morphology. The interleaving protocol consisted of 25 frame/s imaging, with most frames acquired at low-dose except for a high-dose image every 10th frame. This presentation will briefly touch on motion-compensated qDSA with the main focus being on the interleaved angiography technique.