Variation on PSMA receptor expression over time in prostate cancer

Prostate cancer is the third most common cancer in Europe and is still the
leading cancer among men in the Netherlands with over 13,000 men diagnosed each
year. 68-Gallium Prostate Specific Membrane Antigen (68Ga-PSMA) is an emerging
imaging agent that already has been widely proven as a highly effective agent
for restaging PCa cells, but also holds enormous potential for initial staging
and image guided surgery. During surgery, 68Ga-PSMA can potentially be used for
the assessment of resection margins based on Cerenkov Light emission. The
interval between initial staging and subsequent prostatectomy surgery, however,
ranges from 4 to 6 weeks. Since little is known about the PSMA expression over
time without intervention, a study on this is required. If PSMA expression is
equal between both scans, the inclusion and dose determination for image guided
surgery can be based on the clinical 68Ga-PSMA PET/CT scan. In order to
validate this, two PET scans will be performed in a test-retest setting in
primary prostate cancer patients. Dynamic imaging will be performed in order to
get insight into the optimal scan time. Subsequently this will be used also to
establish the ideal timing of surgery after injection.

The objective of this study is to obtain preliminary data on variability in
PSMA expression by comparing the tracer uptake on conventional clinical
68Ga-PSMA PET/CT with an additional 68Ga-PSMA PET/CT (4 weeks later) within
primary prostate cancer patients. Dynamic imaging will be performed in order to
get insight into the most ideal scan time.

This is a prospective observational feasibility study

The aim is to obtain preliminary data on variability in PSMA receptor
expression by comparing uptake within prostate on standard clinical PET/CT with
pre-operative PSMA PET/CT, 4 weeks later.
Primary prostate cancer patients will be included, based upon their MRI, before
their first PET scan. Patients will undergo another PSMA PET-scan within 4
weeks after their standard diagnostic PSMA-PET scan. The protocol for this scan
is equal to standard diagnostic PSMA-PET scan. A PET combined with low dose-CT
for attenuation correction and anatomical correlation will be acquired at
approximately 45 minutes after administration of 68Ga-PSMA.

With 5 patients a dynamic PET/CT-scan (dPET/CT) will be made up to 35 minutes
after administration. Where after a normal skull base to mid femurPET/CT is
made. Within the scans, the patient is requested to void, to improve
visualisation of the prostate on the PET scan.

The patients included in this study have an additional radiation exposure,
since they need to undergo an additional PET-scan prior to surgery, after
injection of the radiotracer 68Ga-PSMA. This will approximatly be 6mSv. The 5
patients for the dynamic scans, will have an additional exposure of 3mSv. The
total exposure llies within the acceptable diagnostic exposure range.