Standard protocol compared to a novel protocol for 68Ga-PSMA-PET/CT in patients with recurrent prostate cancer - which one is superior?

Dijkstra, Lotte; Haupt, Fabian; Viscione, M.; Fech, Viktor; Krause, Thomas Michael; Rominger, Axel Oliver; Afshar Oromieh, Ali (2018). Standard protocol compared to a novel protocol for 68Ga-PSMA-PET/CT in patients with recurrent prostate cancer - which one is superior? European journal of nuclear medicine and molecular imaging, 45(S1), S163-S163. Springer-Verlag

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Purpose / Introduction: Since the clinical introduction of
PET-imaging with 68Ga-PSMA-11, this diagnostic tool has spread
worldwide and is regarded as a breakthrough in the diagnosis
of recurrent prostate cancer (PC). According to its first described
clinical set-up, 68Ga-PSMA-11 PET/CT is conducted at 1h post injection
(p.i.). However, further publications demonstrated that
later imaging (e.g. at 3h p.i.) show the majority of PC lesions with
higher contrast. In 2017, we conducted scans at 1h p.i.. However,
in 2018, we changed our protocol to later imaging timing. The
aim of this evaluation was to compare the standard protocol of
68Ga-PSMA-11 PET/CT with a novel protocol described below.
Subjects & Methods: We retrospectively compared two patient
cohorts scanned with 68Ga-PSMA-11 PET/CT in 2017 (n=94 patients)
and 2018 (n=75 patients). In 2017, the scanning protocol
was as follows: acquisition at 1h p.i. (targeted activity: 200 MBq)
with 2 min per bed position, neither hydration nor forced diuresis.
In 2018, the scans were conducted at 1.5h p.i. (also 2min per
bed position and targeted activity of 200 MBq). In addition, the
patients started to drink 1L of water at 0.5h p.i. and were injected
with 20mg of furosemide at 1h p.i.. Rates of pathologic scans,
maximum standardized uptake values (SUVmax) of tumor lesions
(n=164 in 2017 and n=127 in 2018), average standardized
uptake values (SUVmean) of urinary bladder as well as tumor
contrast (SUVmax-tumor/SUVmean gluteal musculature) were
measured in all patients. Results: Average tumor contrast was
significantly (p=0.0451) higher in 2018 compared to 2017 (59.0
vs. 46.1). Average SUVmean of the urinary bladder was significantly
(p<0.0001) lower in 2018 (SUVmean 7.6 ± 24.6) compared
to 2017 (SUVmean 35.3 ± 7.6). Also the background activity was
significantly (p<0.0001) lower in 2018. No relevant differences
were detected for SUVmax of tumor and the rate of pathologic
scans (2017: 80.9%; 2018: 80%; both numbers for PSA≤3.0 ng/
ml). Discussion / Conclusion: Despite highly promising results
of the novel protocol including significantly higher tumor contrast
and lower urinary activity which enable the assessment
of tumor lesions and local recurrent PC, respectively, no higher
rate of PET-positive patients were observed in the relatively low
patient cohorts. However, we expect that with increasing scan
numbers, more tumor lesions and more pathologic scans will be
detected in a few percent of patients referred to PSMA-PET/CT
thereby changing their therapeutic procedure.

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