Assessment of salivary gland function after 177Lu-PSMA radioligand therapy: Current concepts in imaging and management.

Prostate specific membrane antigen (PSMA) is a transmembrane protein that is highly expressed on prostate epithelial cells and is strongly upregulated in prostate cancer. Radioligand therapy using beta-emitting Lutetium-177 (177Lu)-labeled-PSMA-617, a radiolabeled small molecule, has gained attention as a novel targeted therapy for metastatic prostate cancer, given its high affinity and long tumor retention, and rapid blood pool clearance. In March 2022, the United States Food and Drug administration has granted approval to the targeted 177Lu-PSMA-617 therapy for treatment of patients with PSMA-positive metastatic castration resistant prostate cancer, who have been previously treated with an androgen-receptor pathway inhibitor and taxane-based chemotherapy. Studies have demonstrated the adverse effects of this treatment, mainly encountered due to radiation exposure to non-target tissues. Salivary glands show high PSMA-ligand uptake and receive increased radiation dose secondary to accumulation of 177Lu-PSMA-617. This predisposes the glands to radiation-mediated toxicity. The exact mechanism, scope and severity of radiation-mediated salivary gland toxicity are not well understood, however, the strategies for its prevention and treatment are under evaluation. This review will focus on the current knowledge about salivary gland impairment post 177Lu labeled PSMA-based radioligand therapies, diagnostic methodologies, and imaging with emphasis on salivary gland scintigraphy. The preventive strategies and known treatment options would also be briefly highlighted.

Novel Approaches to Thyroid Cancer Treatment and Response Assessment.

The incidence of thyroid cancer has been increasing. After total thyroidectomy of well-differentiated thyroid tumors with intermediate- or high-risk features on pathology, radioiodine remains one of the mainstays of therapy for both thyroid remnant ablation as well as for treatment of metastatic disease. SPECT/CT, a relatively new modality, has been shown to play a pivotal role predominantly in the post-therapy setting by changing the risk stratification of patients with thyroid cancer. In the case of radioiodine treatment failure, FDG-PET/CT may provide prognostic information based on extent and intensity of metabolically active metastatic sites as well as serve as an important imaging test for response assessment in patients treated with chemotherapy, targeted therapies, or radiotherapy, thereby affecting patient management in multiple ways. The role of newer redifferentiation drugs has been evaluated with the use of I-124 PET/CT.

Positron emission tomography for response assessment in desmoplastic small round cell tumor.

BACKGROUND: Desmoplastic small round cell tumors (DSRCT) typically have a large stromal component and often are extensively disseminated in the peritoneal cavity at diagnosis. These factors contribute to difficulty in quantifying response to chemotherapy using RECIST or WHO criteria. This study compares the overall disease response to chemotherapy by fluorodeoxyglucose-positron emission tomography (FDG-PET) and computed tomography (CT) in patients with DSRCT. METHODS: We conducted a retrospective chart review of 7 patients with DSRCT who were imaged by FDG-PET and CT at diagnosis and after 3 cycles of chemotherapy. Response to chemotherapy was graded according to EORTC metabolic response guidelines and RECIST. RESULTS: All tumors demonstrated some decrease in SUVmax (51%±21%) and longest diameter (23%±8%) with chemotherapy. The best response achieved by FDG-PET was a partial response in 6 patients and by CT was a partial response in 1 patient. Measured response was concordant between the 2 modalities in 2 patients. CONCLUSIONS: In this small series response measurement by FDG-PET did not always correlate with response measurement by CT. A greater decrease in metabolic activity as compared with size was seen in all patients. Further studies are needed to define the role of FDG-PET in assessing early response of DSRCT to chemotherapy.