Molecular imaging with gallium-68 labelled biomolecules

Gallium-68 (T_1/2 = 68 mins) has emerged in the last few years as a highly promising radionuclide for diagnostic imaging with PET. A distinguishing feature of this isotope is that it is obtained by the elution of a small benchtop ⁶⁸Ge/⁶⁸Ga generator in a similar way to the ⁹⁹Mo/^99mTc workhorse of nuclear medicine. As the parent germanium-68 isotope has a half life of 271 day s the ⁶⁸Ge/⁶⁸Ga generator has a useful life of approximately one year. The ⁶⁸Ga radionuclide obtained from the generator is in a suitable chemical form to be directly chelated by small molecules or larger biomolecules bearing a chelating group.¹ Some promising ⁶⁸Ga-labelled radiopharmaceuticals have entered clinical trials, primarily for imaging tumours. The standout and most clinically advanced of the ⁶⁸Ga-based radiopharmaceuticals are the ⁶⁸Ga-labelled octreotide analogs for molecular imaging of somatostatin receptors (SSR) which are overexpressed on the cell surface of neuroendocrine tumours (NETs) and their metastases. Several clinical studies have shown that PET imaging with ⁶⁸Ga-DOTATOC (and similar somatostatin analogs) is superior to conventional ¹¹¹In-DTPA-octreotide SPECT imaging in detecting NETs and metasteses, particularly of small lesions and lesions with low density of somatostatin receptors.^{2,3 68}Ga-DOTATATE PET is superior to ¹⁸F-FDG PET in detecting well differentiated and low grade NETs and is complimentary to ¹⁸F-FDG PET for intermediate and high grade NETs.⁴.