PSMA PET-CT
Skull base to mid-thigh
Typical, not policy
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Staging of high-risk prostate cancer.
- Biochemical recurrence after definitive treatment.
Technique
- The tracer determines the dose and the uptake time, and the two are not interchangeable between agents. Gallium-68 PSMA-11 is typically given at around 1.8-2.2 MBq/kg intravenously, commonly about 100-200 MBq in an adult, with imaging beginning roughly 50-100 minutes after injection and 60 minutes the usual working figure.
- Fluorine-18 PSMA-1007 is typically about 3-4 MBq/kg, commonly around 250-350 MBq, imaged at roughly 90-120 minutes. Fluorine-18 DCFPyL (piflufolastat) is typically around 300-360 MBq with an uptake period of about 60-120 minutes. Confirm the local activity against departmental diagnostic reference levels rather than transferring a figure between tracers.
- No fasting or glucose control is required — this is a receptor-ligand study, not a metabolic one, and the FDG preparation does not apply.
- Excretion route drives the preparation. Gallium-68 PSMA-11 and DCFPyL are substantially renally excreted, so hydration and voiding immediately before acquisition matter, and some centres add a diuretic or delayed pelvic images to clear bladder activity that would otherwise sit over the prostate bed. PSMA-1007 is predominantly hepatobiliary excreted and has little urinary activity, which is why it is often preferred for local recurrence — at the cost of more benign bone uptake foci.
- Acquisition is typically 2-4 minutes per bed position from skull base to mid-thigh, with a low-dose CT for attenuation correction and anatomical localisation; a diagnostic-quality contrast-enhanced CT is acquired only where it is separately indicated.
- Androgen deprivation therapy alters PSMA expression, so the treatment timeline should be recorded on the request — its effect on tracer uptake is time- and duration-dependent and complicates comparison between serial studies.
Where it goes wrong
- PSMA uptake occurs in benign conditions including some bone lesions and ganglia; correlation with the CT component is essential.
- Transferring an activity or an uptake time from one PSMA tracer to another: a gallium-68 dose given with a PSMA-1007 uptake delay, or the reverse, produces an under-counted or poorly timed study.
- Urinary activity in the bladder and distal ureters obscuring the prostate bed on the renally excreted tracers, which is exactly where recurrence is being sought.
Clinical questions that reach this study
Contrast
None
Acquisition
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- Intravenous access adequate for the planned injection· radiographer at scan
- Pregnancy status before an ionising exposure· radiographer at scan