Page 48 - ARNM-2-2

Advances in Radiotherapy
& Nuclear Medicine PET and Compton Camera CZT based system

and activity of radiotherapeutic agents within the patient. in its early stages regarding the efficacy of various PSMA-
However, this leads to non-idealities in positron emission PET imaging techniques for proper prognosis, PSMA-RLT
tomography (PET) imaging as the need for non-pure remains costly, and the limited supply of Lu and Ac
225
177
positron (β ) emitters (positron emitting nuclides with further complicates the situation. However, solving these
+
additional gamma emissions) can cause image degradation challenges would not only reduce costs but also prevent
due to additional gamma emissions overlapping with the unnecessary procedures and limit radiation exposure to
511 keV annihilation photon energy windows. In addition, patients. 12,13
as depicted in Figure 1, non-pure β emitters exhibit A summary of various non-pure β emitters that have
+
+
β range effects where the emitted β particle travels
+
+
significant distances in patient tissue before annihilation piqued the interest of researchers, detailing their properties,
+
occurs, which can cause uncertainty in the true radiotracer such as positron range (β ave) and prompt-gamma (γ)
14-16
distribution. These effects, rooted in physics, present energies, is presented in Table 1. Many of these isotopes
challenges that pre-clinical scanners have yet to overcome are of particular interest for multi-isotope imaging and
despite their exceptional spatial resolution performance. 4,5 radiotheranostics despite having large positron ranges and
multiple prompt-gamma emissions at various energies and
An example where overcoming these challenges is intensities. One notable example is Zr, a non-pure PET
89
useful is in prostate-specific membrane antigen radioligand emitter that emits high-energy gammas; however, it doesn’t
therapy (PSMA-RLT). In clinical settings, PSMA-RLT necessarily qualify as a prompt-gamma emitter due to the
requires the patient to undergo diagnostic PSMA-PET using long half-life of its excited metastable state (t = 16 s). 16-21
1/2
radionuclides such as F and Ga. These radionuclides bind Nonetheless, Zremits a 909 keV gamma with a high yield
18
68
89

to PSMA pharmaceuticals in the form of piflufolastat F of 99% of positron decay. This characteristic gamma of
18
( F-DCFPyL) and Ga-PSMA-11, demonstrating superior 89 Zr allows the possibility of radiolabeling Zr separately
68
18
89
efficacy for prostate cancer diagnosis compared to [ F] from another PET tracer, such as 111 In. This facilitates
18
Fluorodeoxyglucose PET (FDG-PET). Subsequently, the simultaneous identification of separate antigens in
6-8
targeted radiotherapy follows, employing either β-emitting biological tissues. 22
nuclides such as 177 Lu or α emitting nuclides like 225 Ac
attached to PSMA-617. However, Ga, being a non-pure Recent efforts to tackle these challenges have seen efforts
68
β emitter, exhibits properties that are shown to have lower to combine imaging modalities such as PET and Compton
+
spatial resolution compared to F. 9-11 Due to the large mean camera (CC) imaging to increase spatial resolution
18
β range (3.56 mm) and a high energy prompt gamma of through joint reconstruction techniques utilizing high-
+
1.077 MeV of Ga, the correction of β range effects and energy gammas from prompt-gamma emitters. 23-26 The
68
+
the capability to detect and reject high energy gammas are xenon medical imaging system 2 (XEMIS2) is a small
necessary to improve image quality. While research is still animal system aimed to implement triple-gamma (3-γ)

Figure 1. Depiction of positron decay for non-pure positron emitters. Annihilation photons represent the position of positron annihilation position and
not the radionuclide position.

Volume 2 Issue 2 (2024) 2 doi: 10.36922/arnm.3330