F-18 PSMA PET/CT: Piflufolastat Imaging

Fluorine-18–labeled PSMA agents — piflufolastat F-18 (PYLARIFY) and flotufolastat F-18 (POSLUMA) — image prostate cancer by targeting prostate-specific membrane antigen with the favorable physics of fluorine-18: a roughly 110-minute half-life that enables unit-dose distribution without an on-site generator, and a short positron range that supports near scanner-limited spatial resolution. Those two properties change the logistics, image quality, and quantitative quality control (QC) of a PSMA PET program relative to gallium-68 PSMA-11. ¹²⁴

Prostate-specific membrane antigen (PSMA) PET has become a standard tool for staging high-risk prostate cancer and for localizing disease in men with biochemical recurrence after primary therapy. The first widely used agent, gallium-68 PSMA-11, is generator- or cyclotron-produced with a short half-life. The fluorine-18 agents that followed keep the same molecular target but swap in a radionuclide whose decay physics is, from a medical-physics standpoint, easier to work with. This article explains the physics of F-18 PSMA imaging, contrasts it with Ga-68, works through the decay and standardized uptake value (SUV) mathematics, and lays out the QC a quantitative program needs. ¹⁶

Introduction

F-18 PSMA PET/CT combines a molecular target (PSMA, over-expressed on most prostate cancer cells) with a positron-emitting label (fluorine-18) whose half-life and positron energy make it convenient to distribute and quantify. Piflufolastat F-18, also known by its research code 18F-DCFPyL, was FDA-approved in 2021; flotufolastat F-18 (research code rhPSMA-7.3) was approved in 2023 as the second F-18 PSMA agent. ²³⁶

The clinical questions these scans answer — is there nodal or distant metastasis in a newly diagnosed high-risk patient, and where is the disease in a man whose PSA is rising after prostatectomy or radiation — are the same ones Ga-68 PSMA-11 addresses. What differs is the physics of the label, and that physics has practical consequences for the imaging schedule, the achievable spatial resolution, and the discipline required to make SUVs meaningful. ¹⁷

This guide walks through the topic, the key physical principles (with a comparison table and worked decay and SUV mathematics), the clinical impact, practical protocol and QC tips, and the regulatory framework. DRPS supports these programs through its PET/CT and nuclear medicine physics and medical physics consulting services.

Topic Explanation

What is PSMA, and what do the F-18 agents target?

Prostate-specific membrane antigen is a transmembrane glycoprotein over-expressed on the surface of most prostate cancer cells, and its expression tends to increase with tumor grade and in castration-resistant disease. A PSMA-targeted radiopharmaceutical is a small molecule that binds the extracellular enzymatic domain of PSMA and carries a positron-emitting label into the lesion. The label is what the PET scanner detects; the targeting molecule is what makes the signal specific to prostate cancer. ¹⁶

Piflufolastat F-18 and flotufolastat F-18 both use fluorine-18 as the label. Their FDA-approved indications are closely aligned: PET of PSMA-positive lesions in men with prostate cancer who have suspected metastasis and are candidates for initial definitive therapy, or who have suspected recurrence based on an elevated serum PSA. ²³ For the generator-based alternative and its own physics and QC, see our companion guide on Ga-68 PSMA PET/CT.

Why the choice of radionuclide matters

A PET image is only as good as the physics of the photons that form it and the discipline of the calibration behind it. The radionuclide label sets three things a physicist cares about:

Half-life, which controls how far the dose can be shipped, how many patient doses come from a production batch, and how activity decays during uptake and imaging.
Positron energy and range, which set a floor on spatial resolution independent of the scanner's detector design.
Positron branching and other emissions, which affect dosimetry and image quality.

Fluorine-18 scores well on all three, which is a large part of why it became the workhorse radionuclide of clinical PET long before PSMA imaging existed. Applying it to a PSMA ligand inherits those advantages. ⁴⁶

Key Technical Principles

Fluorine-18 versus gallium-68: the physics that matters

The two most common PSMA PET radionuclides differ in ways that a physics program has to plan around. The table below summarizes the practical contrasts.

Property	Fluorine-18 (piflufolastat, flotufolastat)	Gallium-68 (PSMA-11)
Physical half-life	About 110 minutes ²	About 68 minutes
Production and supply	Cyclotron-produced; unit doses shipped from regional radiopharmacies; no on-site generator required	Ge-68/Ga-68 generator or cyclotron; on-site or near-site production
Doses per production	Large batch, many doses; later imaging windows feasible	Limited doses per generator elution
Positron energy	Lower mean positron energy → short positron range → little added blur ⁴	Higher positron energy → longer positron range → measurable resolution/recovery loss unless corrected ⁴⁵
Typical administered activity	Piflufolastat: 333 MBq (9 mCi), range 296–370 MBq ²; flotufolastat: 296 MBq (8 mCi) ³	Weight- or protocol-based, commonly ~150–250 MBq
Uptake time before imaging	About 60 minutes ²³	About 50–60 minutes

The two entries with the biggest downstream consequences are half-life and positron range.

Half-life and distribution logistics

Fluorine-18's 110-minute half-life is roughly 1.6 times that of gallium-68. That difference compounds over the hours between production and imaging. A cyclotron radiopharmacy can synthesize a large batch of an F-18 PSMA agent in the morning and ship unit doses to imaging centers across a region, which then scan patients through the day without owning a generator or a cyclotron. Gallium-68, with its shorter half-life and generator-limited elution, ties production much more tightly to the scan schedule. ¹²

This logistics advantage is why many centers without radiochemistry infrastructure can offer PSMA PET at all: the dose arrives the way an F-18 FDG dose does. It also means the physics of decay during shipping, uptake, and imaging is central to getting the activity — and therefore the SUV — right.

Worked decay example

Fluorine-18 decays with a half-life $T_{1/2} \approx 110$ minutes, so its decay constant is:

λ = \frac{ln 2}{T _{1/2}} = \frac{0.693}{110 min} \approx 0.00630 min^{- 1}

If a dose is calibrated to 333 MBq and the patient is imaged 60 minutes after injection, the activity remaining at the start of imaging is:

A (t) = A_{0} e^{- λ t} = 333 \times e^{- 0.00630 \times 60} = 333 \times e^{- 0.378} \approx 333 \times 0.685 \approx 228 MBq

About 68.5 percent of the injected activity remains at imaging. For gallium-68, with its shorter half-life, the same 60-minute uptake would leave a substantially smaller fraction — one reason F-18 agents tolerate longer or more flexible uptake and imaging windows. This decay factor is not academic: it is exactly the correction that must be applied to make quantitative SUVs valid. ¹

Positron range and spatial resolution

When a positron is emitted, it travels a short distance in tissue, losing energy, before it annihilates with an electron and produces the two 511 keV photons the scanner detects. Because the annihilation happens away from the emitting nucleus, the positron range blurs the reconstructed image — a resolution limit that is a property of the radionuclide, not the scanner. ⁴

Fluorine-18 emits relatively low-energy positrons, so its mean positron range in tissue is short — well below the intrinsic spatial resolution of clinical PET — and it contributes little additional blur. Gallium-68 emits substantially higher-energy positrons with a longer range, which measurably degrades spatial resolution and lesion recovery. Monte Carlo and phantom work characterizing positron range across radionuclides confirms this ordering, and clinical-scanner studies show that applying gallium-68 positron-range correction can improve reconstructed spatial resolution and recovery coefficients — quantifying the head start that fluorine-18 has without any correction at all. ⁴⁵ For a deeper treatment of this resolution limit, see PET spatial resolution and positron range.

SUV: the quantitative endpoint

The standardized uptake value normalizes the measured activity concentration in a lesion to the injected activity per unit body mass, so that a number roughly independent of dose and patient size can be trended and compared. The body-weight SUV is:

SU V_{bw} = \frac{C _{ROI}}{A _{dc} / w}

where $C_{ROI}$ is the decay-corrected activity concentration in the region of interest (for example, MBq/mL), $A_{dc}$ is the injected activity decay-corrected to the scan time, and $w$ is body weight (with 1 mL of tissue ≈ 1 g). Using the decay example above, suppose the injected activity decay-corrected to imaging is $A_{dc} = 228$ MBq, the patient weighs 80 kg (≈ 80,000 mL), and a PSMA-avid node measures $C_{ROI} = 0.0285$ MBq/mL:

SU V_{bw} = \frac{0.0285}{228/80 , 000} = \frac{0.0285}{0.00285} = 10.0

An SUV of 10 is a strong PSMA signal. But every input in that equation depends on calibration: the injected activity comes from the dose calibrator, the decay correction from the clock and half-life, and the concentration from the scanner's cross-calibration to that same dose calibrator. An error anywhere propagates directly into the SUV — which is why quantitative PSMA imaging is fundamentally a QC problem, not just an acquisition problem. ¹⁸ For the full treatment of this endpoint, see PET SUV quantification.

Clinical Impact

The physics advantages of F-18 PSMA translate into access, image quality, and quantitative reproducibility — but only when the calibration chain is disciplined. The 110-minute half-life is what lets a community imaging center without a cyclotron or generator offer PSMA PET at all, broadening access to accurate staging and recurrence localization. The short positron range means the intrinsic resolution penalty is small, so small nodes and bone lesions are rendered with less radionuclide-driven blur than with gallium-68. ¹⁴

Quantitatively, repeatability studies of piflufolastat F-18 PET/CT have characterized how reproducible SUV measurements are on repeat imaging, which is the foundation for using SUV change as a response or progression signal. ⁸ Detector generation matters too: comparisons of digital versus analog PET/CT with piflufolastat F-18 show that scanner hardware affects lesion detection and quantitation, so a site's platform is part of the quantitative story. ⁹ And agent-specific pharmacology has practical consequences — for flotufolastat F-18, a prospective trial showed that forced diuresis during imaging improved recurrence detection after prostatectomy by reducing bladder activity that can obscure nearby recurrence. ¹⁰

None of these benefits survive a broken calibration chain. A scanner that is not cross-calibrated to the dose calibrator, a clock that drifts, or an uptake time that varies patient to patient will produce SUVs that look precise but are not accurate. The clinical value of F-18 PSMA is realized only on top of a quantitative QC program. ¹⁸

Practical Optimization Tips

Protect the quantitative chain

Calibrate the dose calibrator and cross-calibrate the scanner. The scanner's activity concentration must trace back to the same dose calibrator that measures the injected dose, or SUVs are meaningless. Verify the cross-calibration on the schedule your QC program and accreditation require.
Synchronize clocks. Decay correction depends on the elapsed time between assay and scan. The dose-calibrator clock, the injection-time record, and the scanner clock must agree; a few minutes of drift shifts every SUV.
Standardize uptake time. Because uptake and washout are time-dependent, hold the injection-to-scan interval as close to the protocol target (about 60 minutes) as workflow allows, and record it. Variable uptake time is a leading, avoidable source of SUV variability. ¹

Standardize acquisition and reconstruction

Fix the reconstruction. SUV depends on the reconstruction algorithm, iterations, filtering, and corrections. Lock these for quantitative work so serial scans are comparable, and document any change.
Use harmonization when comparing across sites or trials. Programs such as EANM/EARL exist specifically to make SUVs comparable across scanners and centers; adopt them when cross-site comparison or trial participation is in scope. ¹² See also our guide to EARL SUV harmonization.
Report consistently. Standardized reporting frameworks for PSMA PET (for example, the EANM E-PSMA guidelines) reduce interpretive variability and make quantitative statements comparable between readers. ¹¹

Verify performance at acceptance and over time

Do NEMA NU-2 performance testing at acceptance. Sensitivity, spatial resolution, noise-equivalent count rate, and image quality establish the baseline a quantitative program is built on. See PET/CT NEMA NU-2 performance testing. ¹
Run daily QC and trend it. Daily calibration and QC catch drift before it corrupts SUVs; trending is what reveals slow problems a single day's pass/fail can hide.
Match agent pharmacology to protocol. For agents where bladder activity can obscure pelvic recurrence, incorporate the label's approved strategies (for example, hydration or diuresis and immediate pre-scan voiding) as clinically appropriate. ²¹⁰

Regulatory Considerations

F-18 PSMA imaging sits at the intersection of FDA drug approval and NRC or Agreement State materials regulation. The agents themselves are FDA-approved radiopharmaceuticals with prescribing information that specifies indication, administered activity, and imaging timing; the radioactive material is byproduct material governed for medical use by the NRC or an Agreement State. ²³⁴

Key frameworks:

FDA prescribing information. Piflufolastat F-18 (PYLARIFY) recommends 333 MBq (9 mCi), range 296–370 MBq, with imaging about 60 minutes after injection; flotufolastat F-18 (POSLUMA) recommends 296 MBq (8 mCi), also imaged about 60 minutes after administration. Administered-activity and timing decisions should follow the current label. ²³
10 CFR Part 35 — Medical Use of Byproduct Material. Governs authorized users, written directives where applicable, and the radiation safety program for medical-use radionuclides, including diagnostic PET agents.
10 CFR Part 20 — Standards for Protection Against Radiation. Sets occupational and public dose limits that shape hot-lab handling, injection workflow, and post-injection patient management for these positron emitters.
Joint EANM/SNMMI PSMA PET/CT procedure standard (version 2.0). Provides consensus procedure guidance for prostate cancer PSMA PET/CT, including acquisition and interpretation considerations that support consistent, high-quality imaging. ¹

Of the states DRPS serves, Florida, Maryland, Virginia, California, Nevada, Pennsylvania, New York, and New Jersey are NRC Agreement States that license medical use under their own radiation-control programs, while Washington, DC and Delaware are regulated directly by the NRC for byproduct material. A facility must confirm which authority issues its license and which requirements apply. Because the CT component of PET/CT is a radiation-producing machine, it is additionally regulated under state radiation-machine programs. Coordinating the drug label, the materials license, and the CT program is part of a defensible PSMA PET service.

Frequently Asked Questions (FAQs)

What is F-18 PSMA PET/CT?

F-18 PSMA PET/CT is a positron emission tomography scan that uses a fluorine-18–labeled small molecule targeting prostate-specific membrane antigen (PSMA) to image prostate cancer. Two FDA-approved agents are piflufolastat F-18 (PYLARIFY) and flotufolastat F-18 (POSLUMA). Both are used to detect PSMA-positive lesions in men with suspected metastasis or biochemical recurrence. ²³

How is F-18 PSMA different from Ga-68 PSMA?

Fluorine-18 has a 110-minute half-life versus about 68 minutes for gallium-68, and it emits lower-energy positrons with a shorter range, which supports slightly better intrinsic spatial resolution. The longer half-life lets F-18 agents be produced in a cyclotron and shipped as unit doses to sites without an on-site germanium-68/gallium-68 generator. ²⁴

How much activity is administered for piflufolastat F-18?

The FDA prescribing information for piflufolastat F-18 (PYLARIFY) recommends 333 MBq (9 mCi), with an acceptable range of 296 to 370 MBq (8 to 10 mCi), given as a single intravenous bolus, with imaging beginning about 60 minutes after injection. ²

Why does positron range matter for image quality?

A positron travels a short distance before annihilating, and that distance blurs the reconstructed image because the 511 keV photons originate away from the emitting nucleus. Fluorine-18's short positron range contributes little blur, while gallium-68's higher positron energy adds measurable degradation to spatial resolution and lesion recovery unless positron-range correction is applied. ⁴⁵

Is the SUV comparable between F-18 and Ga-68 PSMA scans?

Standardized uptake values depend on the radionuclide's physics, the scanner, the reconstruction, and the uptake time, so SUVs are not automatically interchangeable across agents or systems. Quantitative comparison requires consistent protocols and scanner calibration, and harmonization programs exist to make SUVs more comparable across sites. ¹¹²

What QC does a quantitative F-18 PSMA program need?

A quantitative PSMA PET program needs an accurate dose calibrator, PET/CT scanner calibration traceable to the dose calibrator and clock, NEMA NU-2 performance testing at acceptance, routine daily QC, and controlled uptake time and reconstruction settings. A medical physicist ties these together so SUVs are accurate and reproducible. ¹⁸

Who regulates F-18 PSMA imaging agents?

The imaging agents are byproduct material regulated for medical use under 10 CFR Part 35 or the equivalent Agreement State program, with dose limits under 10 CFR Part 20, while the drugs themselves are FDA-approved radiopharmaceuticals. A qualified medical physicist and the authorized user share responsibility for safe, accurate use. ²³

Key Takeaways

F-18 PSMA agents pair PSMA targeting with fluorine-18's favorable physics. Piflufolastat F-18 and flotufolastat F-18 are FDA-approved agents for prostate cancer PSMA PET. ²³
The 110-minute half-life drives access. Cyclotron production and unit-dose distribution let sites without a generator offer PSMA PET, and it eases uptake and imaging scheduling. ¹²
Short positron range supports resolution. Fluorine-18 adds little radionuclide blur, while gallium-68's longer range measurably degrades resolution and recovery unless corrected. ⁴⁵
SUV is a calibration problem. Every SUV depends on the dose calibrator, clock synchronization, decay correction, scanner cross-calibration, uptake time, and reconstruction. ¹⁸
Quantitative QC is the foundation. NEMA NU-2 testing, daily QC, harmonization, and standardized reporting turn the physics advantage into reproducible numbers. ¹¹¹¹²
Two regulators apply. FDA governs the drug label; the NRC or an Agreement State governs the byproduct material under Parts 35 and 20. ²³

Conclusion

F-18 PSMA PET/CT takes a proven molecular target and pairs it with the radionuclide that made clinical PET practical in the first place. The 110-minute half-life broadens access by decoupling imaging from on-site production, and the short positron range keeps the radionuclide's contribution to blur small. But the same physics that makes these agents convenient also makes them demanding: their quantitative value — the SUV that clinicians trend for staging and response — is only as trustworthy as the dose calibrator, the clocks, the cross-calibration, the uptake time, and the reconstruction behind it. A facility that treats F-18 PSMA imaging as a calibrated, QC-driven quantitative program, not just an acquisition, gets the full benefit of the physics. ¹²⁸

How DRPS Can Help

Diagnostic Radiation Physics Services (DRPS) supports PET/CT and nuclear medicine facilities with PET/CT and nuclear medicine physics, NEMA NU-2 acceptance and performance testing, dose-calibrator and scanner cross-calibration, SUV harmonization support, quantitative QC program design, and medical physics consulting prepared by board-certified medical physicists. DRPS serves facilities across Florida, Maryland, Virginia, Washington DC, California, Nevada, New York, Pennsylvania, New Jersey, and Delaware — see our service locations.

A strong PSMA PET program is not just about acquiring images. It is about making sure the numbers those images produce are accurate, reproducible, and defensible.

Related Resources

References

Fendler WP, Eiber M, Beheshti M, et al. PSMA PET/CT: joint EANM procedure guideline/SNMMI procedure standard for prostate cancer imaging 2.0. European Journal of Nuclear Medicine and Molecular Imaging. 2023;50(5):1466-1486. doi:10.1007/s00259-022-06089-w. PubMed
U.S. Food and Drug Administration. PYLARIFY (piflufolastat F 18) injection prescribing information. 2021. accessdata.fda.gov
U.S. Food and Drug Administration. POSLUMA (flotufolastat F 18) injection prescribing information. 2023. accessdata.fda.gov
Carter LM, Kesner AL, Pratt EC, et al. The impact of positron range on PET resolution, evaluated with phantoms and PHITS Monte Carlo simulations for conventional and non-conventional radionuclides. Molecular Imaging and Biology. 2020;22(1):73-84. doi:10.1007/s11307-019-01337-2. PubMed
Gavriilidis P, Koole M, Annunziata S, et al. Performance evaluation of iterative PET reconstruction with resolution recovery incorporating Gallium-68 positron range correction. Medical Physics. 2024;51(9):5927-5942. doi:10.1002/mp.17259. PubMed
Voter AF, Werner RA, Pienta KJ, et al. Piflufolastat F-18 (18F-DCFPyL) for PSMA PET imaging in prostate cancer. Expert Review of Anticancer Therapy. 2022;22(7):681-694. doi:10.1080/14737140.2022.2081155. PubMed
Mena E, Lindenberg ML, Turkbey IB, et al. 18F-DCFPyL PET/CT imaging in patients with biochemically recurrent prostate cancer after primary local therapy. Journal of Nuclear Medicine. 2020;61(6):881-889. doi:10.2967/jnumed.119.234799. PubMed
Jansen BHE, Cysouw MCF, Vis AN, et al. Repeatability of quantitative 18F-DCFPyL PET/CT measurements in metastatic prostate cancer. Journal of Nuclear Medicine. 2020;61(9):1320-1325. doi:10.2967/jnumed.119.236075. PubMed
Maliha PG, Nolet B, Ebrahim A, et al. Comparing digital to analog PSMA-targeted piflufolastat 18F PET/CT in prostate cancer patients in early biochemical failure. Nuclear Medicine Communications. 2023;44(3):187-193. doi:10.1097/MNM.0000000000001652. PubMed
Lawal IO, Mushtaq A, Jani AB, et al. Diuresis during 18F-flotufolastat (rhPSMA-7.3) PET/CT improves recurrence detection after prostatectomy: a prospective phase II trial. Journal of Nuclear Medicine. 2025;66(2):230-237. doi:10.2967/jnumed.124.268574. PubMed
Ceci F, Oprea-Lager DE, Emmett L, et al. E-PSMA: the EANM standardized reporting guidelines v1.0 for PSMA-PET. European Journal of Nuclear Medicine and Molecular Imaging. 2021;48(5):1626-1638. doi:10.1007/s00259-021-05245-y. PubMed
Aide N, Lasnon C, Veit-Haibach P, et al. EANM/EARL harmonization strategies in PET quantification: from daily practice to multicentre oncological studies. European Journal of Nuclear Medicine and Molecular Imaging. 2017;44(Suppl 1):17-31. doi:10.1007/s00259-017-3740-2. PubMed
U.S. Nuclear Regulatory Commission. 10 CFR Part 35: Medical Use of Byproduct Material. ecfr.gov