Page 109 - New epidemiological and PSMA-expression based paradigms in salivary gland tumors
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Distribution of PSMA-ligand in salivary and lacrimal glands on PET/CT
preliminary results show staining of serous and mucous acinar cells as well as small (intercalated and striated) duct cells. In the present study, minor salivary glands had lower SUVmax values than major glands (Table I). Most likely, this is associated with gland volume. Additionally, it is currently unclear whether this difference in SUV values also reflects a biological difference between the gland types, e.g., a lower number of specific present cells per volume. Direct evidence of a relation between functional capacity and PSMA-tracer uptake is expected to be provided by future research. The limited spatial resolution of current PET/CT scanners may introduce partial volume errors. For objects smaller than the voxel size, the measured tracer concentration is less than the true tracer concentration value in tissue. This could have led to a significant underestimation of the actual tracer uptake in the minor salivary and seromucous glands [30].
The lacrimal glands: Many considerations about the salivary and seromucous
glands apply similarly to the serous lacrimal glands that show a comparably high
tracer accumulation in PSMA PET/CT. The main lacrimal glands are located in 6 the superolateral orbit and each consists of two lobes that are separated by an aponeurosis [31]. There is currently insufficient knowledge regarding PSMA
expression patterns in lacrimal gland cells.
Clinical potential of PSMA-PET/CT: The ability to specifically bind PSMA in salivary and seromucous glandular tissue may open the door to several potential applications of PSMA-ligand binding and imaging of the head and neck area using PET/CT. In oncology, PSMA PET/CT may be used for the detection of recurrent and metastatic salivary gland cancers, squamous cell carcinomas, or even benign salivary gland tumors [25,26]. To differentiate salivary gland tumors from normal glandular tissue, knowledge of the level of physiological uptake is important. Furthermore, in external beam radiotherapy of the head and neck, it might be possible to selectively spare previously invisible salivary gland locations, especially areas with a high concentration of minor glands. When the location and functional relevance of these glands have been revealed, the amount of radiation dose that passes through these tissues can be reduced by optimization of the treatment plan. This minimize the risk of a persistent xerostomia and associated reduced quality of life [32]. In addition, PSMA PET/CT may identify gland locations devoid of PSMA-ligand uptake, which may not need sparing and thus provide greater flexibility in treatment planning.
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