No abstract

Radioembolization with 90 Y microspheres represents a novel transarterial radiation treatment for liver tumors. The purpose of this pilot study was to evaluate the findings of postimplantation PET/CT of 90 Y glass microspheres. Methods: Three patients with hepatocellular carcinoma and 2 patients with liver metastases (1 neuroendocrine, 1 colorectal) underwent PET/CT after radioembolization. Four patients underwent imaging at 1 mo to assess response and confirm PET/CT findings; 1 patient underwent PET/CT at 4 d after 90 The tracer 90 Y is traditionally thought of as a pure b-emitter. Thus, current clinical practice involves determining the distribution of the microspheres through bremsstrahlung imaging combined with anatomic imaging via SPECT/CT (1). Because bremsstrahlung imaging is based on a SPECT acquisition that uses either a wide imaging window or multiple energy windows due to the continuum, the scattered photon cannot easily be distinguished from true photons. Consequently, bremsstrahlung imaging is not quantifiable, and thus accurate dose distribution cannot be obtained (2).In an effort to improve pretreatment evaluation and follow-up, microspheres containing radionuclides that emit both b-and g-radiations have been proposed, and treatment with microspheres includes the use of 166 Ho and 186 Re/ 188 Re. At the time of this article's publication, glass and poly (L-lactic acid) (PLLA) microspheres incorporating 186 Re/ 188 Re had not been tested in human subjects with liver tumors. However, 188 Re human serum albumin microspheres ( 188 Re-HSAM) have been tested in a small cohort of patients at a single institution (3). The maximum b-particle energy of 188 Re (2.12 MeV) is lower than that of 90 Y (2.28 MeV), thus necessitating 4-to 5-fold-higher activities to obtain an absorbed dose equivalent to that of 90 Y. Because the g-energy (155 keV) is comparable to other nuclear medicine imaging agents, 188 Re-HSAM seems to be a good candidate for radioembolization of liver tumors. However, no conclusive effects could be derived from the study performed by Liepe et al. because of the small cohort size and heterogeneity of the patients' primary disease (3). To properly evaluate the effect of radioembolization of hepatic malignancies with 188 Re-HSAM, more studies and a larger patient cohort are warranted.Another promising radionuclide proposed for radioembolization of hepatic tumors is 166 Ho (maximum energy of the b-particle, 1.77 [48.7%] and 1.85 [50.5%] MeV and energy of the g-ray, 81 keV [6.7%]). 166 Ho PLLA microspheres are currently being used in patients with hepatic malignancies under a phase I clinical trial (4,5). Similar to the 188 Re HSAM dosimetry, the absorbed radiation dose per activity of 166 Ho (8.7 mGy/MBq) is lower than that of 90 Y (28 mGy/MBq). As a result, with 166 Ho 3 times the radioactivity will be required for radioembolization to achieve a dosimetry equivalent to that of 90 Y. The greatest advantage of 166 Ho is that it represents a multimodality imaging agent (6). The paramagnetic pro...

A 64-year-old man with a known case of right parietal lobe glioblastoma multiforme operated on in August 2018 was referred for 18F-FDG PET/CT with a clinical suspicion of recurrence. He underwent 18F-FDG and 18F-PSMA 1007 scans. Both the scans showed intense tracer uptake in right parietal lobe lesion, which concurred with MRI findings of recurrent disease and was later proven on histopathologic examination as recurrence. Our case highlights the feasibility of 18F-PSMA 1007 PET/CT imaging of suspected glioblastoma recurrence. Considering its similarity to PSMA-617, it may be used as a surrogate imaging tracer for potential theranostic application using alpha or beta emitters.

A 46-year-old man with end-stage renal disease and renal cell carcinoma underwent 18F-FDG PET/CT for initial staging followed by 18F-PSMA-1007 PET/CT. Unlike 18F-FDG, which undergoes renal clearance, 18F-PSMA-1007 undergoes hepatobiliary clearance and thus generates superior quality images. 18F-PSMA-1007 PET/CT showed intense tracer-avid left renal mass lesion (FDG nonavid); lytic bone lesions (FDG avid) and single liver lesion (FDG nonavid). This case highlights the superiority of 18F-PSMA-1007 over 18F-FDG PET/CT in identifying primary lesion as well as metastatic sites in case of renal cell carcinoma even in the presence of end-stage renal disease.

Our weight-based dose protocol showed a significant reduction in absorbed doses (i.e. 69.14% for F-NaF and 67.45% for technetium-99m-methylene diphosphonate) when compared with fixed dose method guidelines of SNMMI. It is suggested that further prospective studies may be performed in adult population, to evaluate dosimetry efficacy of F-NaF at a low dose of 0.06 mCi/kg as inferred in our current study.