Page 117 - New epidemiological and PSMA-expression based paradigms in salivary gland tumors

PSMA PET/CT: as a tool to assess and guide salivary gland irradiation
Introduction
External beam radiotherapy (RT) can cause damage to salivary glands, resulting in
xerostomia and reduction of quality of life [1,2]. Evaluation of glandular function
is currently limited to patient-reported outcomes measures, or to laborious and
poorly quantifiable procedures such as gland cannulation or planar scintigraphy
during stimulated salivation[3]. This limits objective evaluation of toxicity, for
example for voxel-based evaluations or anticipated comparison of regular intensity
modulated radiotherapy (IMRT) with new modalities like proton treatment.
Based on clinical observations, our hypothesis was that a molecular imaging of
the prostate-specific membrane antigen (PSMA) using radiolabelled ligands and
positron emission tomography combined with computed tomography (PET/
CT) can be used to visualise and quantify viable gland cells in salivary glands.
Functional imaging with PSMA PET/CT is generally applied for sensitive and
specific (re)staging of prostate carcinoma [4,5]. Normal salivary and seromucous
glands have recently been shown to consistently demonstrate high uptake of PSMA-ligand (figure 1) [6,7]. The function of the PSMA epitope in salivary gland
tissue has not yet been elucidated, but the expression is reported to be located
in secretory glandular (acinar) cells [8]. This theoretically enables sensitive and 7 selective imaging of the presence of acinar gland cells in both major and previously undetectable minor salivary glands, and to quantify loss of these cells in a gland-
specific and voxel-based approach [9].
We aimed to identify and introduce PSMA PET/CT as a possible new application to guide radiotherapy, in a first observational report.
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