68Ga-PSMA PET/CT or PET/MRI in Evaluating Patients With Recurrent Prostate Cancer: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for 68Ga-PSMA PET/CT or PET/MRI in Evaluating Patients With Recurrent Prostate Cancer (NCT02488070), a na phase 1, phase 2 study. The primary outcome is Average SUVmax of Ga68 PSMA Uptake Outside the Expected Normal Biodistribution.

2. Clinical Question

The clinical question is diagnostic and descriptive rather than a comparison of treatment effects. The study used a radiopharmaceutical that localizes to a specific prostate cancer receptor, followed by PET/CT or PET/MRI imaging. The primary endpoint describes the maximum uptake within visually appreciable focal regions outside expected normal biodistribution; it is not a measure of clinical benefit, diagnostic accuracy, or patient outcome. Feasibility of the scan was listed as a secondary outcome, but its result is not reported in the registry record. The record also does not report how the two imaging modalities were assigned or whether participants underwent both. The study therefore supports a narrowly framed question about imaging and uptake, not a conclusion about one modality being better than another.

3. Trial Design

This completed feasibility study was registered as a phase 1 and phase 2, single-group study with no masking. The registry lists allocation as NA and enrollment of 10. Its title identifies 68Ga-PSMA PET/CT or PET/MRI in patients with recurrent prostate cancer. The listed diagnostic group received gallium Ga 68-labeled PSMA ligand Glu-urea-Lys(Ahx) intravenously, followed by PET/CT or PET/MRI approximately 45-60 minutes later.

The registry record gives a start date of 2015-06 and a primary completion date of 2015-08, and lists the study status as completed. Stanford University is identified as the sponsor. The study was not a randomized comparison, and its single-group structure does not establish a like-for-like control group. The record does not report a protocol for selecting PET/CT versus PET/MRI, or whether the same participants received both procedures.

The primary outcome was the average SUVmax of Ga68 PSMA uptake outside the expected normal biodistribution, with a timeframe described as an estimated average of 1 hour. The record states that 45 areas of high focal uptake were used to calculate this average, and that mediastinal blood pool served to determine average background. Feasibility of the Ga-68 PSMA PET/CT or PET/MRI scan was listed as a secondary outcome. Five outcome measures are recorded, but details of the other measures are not reported in the registry record. There are no analysis entries. No protocol for image interpretation, outcome adjudication, or handling of repeated measurements is reported in the registry record.

These design features matter for interpretation. An unmasked, single-group imaging study can describe what was measured in its enrolled participants, but it cannot by itself separate an imaging finding from differences between randomized groups. The limited enrollment also means the study is framed as a feasibility investigation rather than as a definitive comparison. The registry record does not report a sample-size justification or a statistical analysis plan.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

Analysis population for the primary outcome, as defined in the registry: 45 areas of high Ga68 PSMA focal uptake outside the normal biodistribution were used to calculate the average SUVmax. The mediastinal blood pool was used to determine average background.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Average SUVmax of Ga68 PSMA Uptake Outside the Expected Normal Biodistribution, measured over an estimated average of 1 hour.

The primary endpoint is the average SUVmax for Ga68 PSMA uptake in areas outside the expected normal biodistribution. SUVmax is a semiquantitative measure of the maximum radiopharmaceutical uptake within a region of interest. The registry describes identifying areas with visually appreciable increased focal uptake over background, drawing regions of interest around those areas, and calculating SUVmax. The mediastinal blood pool was used to determine average background.

The endpoint summarizes uptake across 45 areas of high focal uptake. It is therefore a measure defined over selected regions, rather than a direct count of participants with cancer or a measure of diagnostic accuracy. The registry record does not report how the regions were selected beyond the visual description, how many regions came from each participant, or how readers assessed images. Those details affect how reproducible the measure may be and how the average should be interpreted.

In general, a continuous measure such as SUVmax can describe the magnitude of an imaging signal, while an average provides a summary across the measured regions. A standard deviation, if reported, would describe how dispersed individual region measurements were around the mean; it would not itself establish the precision of the mean. The endpoint’s intended use is to characterize the distribution of uptake outside expected physiologic locations in this feasibility setting. A numerical mean and standard deviation are not reported in the registry record, so the magnitude and variability of the observed uptake cannot be assessed from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Several statistical ideas are relevant to interpreting this study, even though the registry record does not document a full analysis plan or provide numerical endpoint results. The explanations below are general unless they refer directly to a study feature stated in the registry record.

What does the primary measure summarize?

The outcome is a continuous measure: SUVmax, a semiquantitative value for maximum radiopharmaceutical uptake within a region of interest. The registry describes drawing regions around visually appreciable focal uptake above mediastinal blood-pool background and calculating a value for each region. An average across the selected regions gives a summary of their measured uptake. It does not describe every location in the body, and it does not by itself classify a scan as positive or negative.

A mean is useful when the question concerns the average magnitude of a continuous measurement. It can, however, be affected by unusually high or low values. A standard deviation describes the spread of measurements around the mean. It is not the same as a standard error or a confidence interval: the standard deviation describes variation among measurements, whereas the latter quantities describe uncertainty in an estimate. The registry identifies standard deviation as the dispersion measure but does not report its value.

Why does the unit of analysis matter?

The registry says 45 areas were used to calculate the average, while enrollment was 10 participants. This means the reported endpoint is described in terms of regions, not simply as a single independent observation for every participant. In general, multiple regions from one person can share characteristics and therefore be correlated. Analyses that account for within-participant clustering can produce different uncertainty estimates from analyses that treat every region as independent.

The registry record does not report how regions were distributed across participants, whether any participant contributed multiple regions, or how the analysis handled that structure. This makes it impossible to determine from the registry record whether the mean and any uncertainty measure were calculated with an appropriate unit of analysis. In a small feasibility study, describing both the number of participants and the number of measured regions is particularly important because these counts answer different questions.

What can a confidence interval tell a reader?

General explanation: a confidence interval gives a range of values compatible with an estimate under the specified statistical model and sampling assumptions. Its width reflects statistical precision. A confidence interval is not a guarantee that the true value lies within the interval, and it does not address all sources of bias or measurement error. For this endpoint, no confidence interval is reported in the registry record. Without an estimate and interval, readers cannot judge the numerical magnitude or statistical precision of the average SUVmax.

Why are over-dispersion and distribution relevant?

General explanation: some continuous outcomes vary more than a simple statistical model expects. This is often called over-dispersion, and ignoring it can make uncertainty estimates too small. The distribution of SUVmax values, potential extreme values, and clustering across participants would all be relevant when choosing an analysis. The registry record does not report the individual measurements or a distributional assessment, so it is not possible to evaluate whether a particular model would be suitable.

For an average, the mean and standard deviation are informative summaries, but they do not reveal the full shape of a distribution. A few extreme measurements can influence a mean; a median or a plot of individual values can add useful context. No such numerical summaries or analysis details for the primary endpoint are reported in the registry record.

What does the study design permit?

This is a single-group study with allocation listed as NA and no masking. General explanation: random allocation can help balance measured and unmeasured characteristics between comparison groups, while masking can reduce some influences on measurement or interpretation. Neither feature is reported for this study. Since the study has no separate randomized comparator, it is not designed to estimate a controlled difference between PET/CT and PET/MRI. The registry record also does not report whether modality choice was based on clinical or logistical considerations.

The registry’s planning-illustration assumptions describe a two-arm setting, equal allocation, a two-sided significance level of 0.05, and a normal approximation. They are not the analysis plan for this single-group study. Planning calculations describe hypothetical enrollment requirements under chosen assumptions; they are not observed power and do not establish that an actual study can detect an effect. The trial’s own sample-size justification is not reported in the registry record.

What can be inferred from the absence of analysis entries?

The registry lists no analysis entries. This indicates that no analysis is documented in that portion of the registry record; it should not be translated into a claim that no analysis was conducted. The registry record does not report a statistical analysis plan, prespecified hypotheses, handling of missing measurements, or methods for uncertainty estimation. Without those details, statistical interpretation should remain descriptive and cautious.

General explanation: a prespecified analysis plan helps distinguish planned analyses from choices made after observing data. It can specify the outcome definition, analysis population, handling of multiple outcomes, missing-data procedures, and model assumptions. These details are especially relevant when several outcomes are recorded or when measurements are clustered. The registry record does not report those procedures, so it is not possible to determine how analytical decisions were made.

In short, the endpoint is a continuous imaging summary based on selected regions, and its interpretation depends on region selection, participant-level clustering, measurement consistency, and statistical uncertainty. The registry record defines the broad measurement approach but does not report the numerical results or enough analysis detail to evaluate those issues.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Diagnostic (68Ga-PSMA PET/CT or PET/MRI)")
n   <- c(10)
m   <- c(12.4)
sp  <- c(7.1)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Diagnostic (68Ga-PSMA PET/CT or PET/MRI)  10  12.400  7.100  7.321  17.479

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists five outcome measures, identifies average SUVmax as the primary outcome, and lists feasibility of the Ga-68 PSMA PET/CT or PET/MRI scan as a secondary outcome. The other outcome measures are not described in the registry record. No analysis entries are listed, and a statistical analysis plan is not reported in the registry record.

General explanation: when a study assesses multiple outcomes or performs multiple statistical tests, the chance of at least one apparently unusual result can increase. A prespecified hierarchy, adjustment procedure, or clear distinction between primary and exploratory analyses can help readers understand how findings should be interpreted. The registry record does not report a multiplicity strategy. Because numerical results and analysis entries are absent, it is not possible to assess whether or how multiplicity affected reported findings.

The registry record does not report missing-data counts, exclusions from the endpoint analysis, or a method for handling missing measurements. It also does not define an analysis population beyond describing the 45 areas used for the primary average and enrollment of 10. Readers therefore cannot determine whether all enrolled participants contributed data, whether all measured regions were included, or how incomplete imaging data were treated. These are not assumptions that can be filled in from the study title or endpoint description.

General explanation: missingness can affect estimates when the chance that data are absent is related to participant characteristics or to the outcome itself. Different missing-data methods rely on different assumptions, and a complete-case analysis can be difficult to interpret if missingness is substantial or systematic. No missing-data method is reported in the registry record, so the impact of missing measurements cannot be evaluated.

The record’s lack of analysis entries should be read as a limitation of the documented analysis information, not as proof that analyses were never performed. The protocol for analysis populations, multiplicity, and missing data is not reported in the registry record.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry lists one diagnostic group, with 10 participants at risk for serious adverse events and 0 participants affected. It also lists 10 participants at risk for other adverse events and 0 participants affected, and reports 0 deaths. These are the event counts recorded for the group. They are not estimates of comparative safety because the study has no separate control group.

A count of zero affected participants means that no participants were recorded as having the listed event category in this registry entry. It does not establish that an event is impossible or that the imaging procedure has no risk. In general, small studies may be unable to characterize uncommon events precisely, and observed counts depend on the period and methods used to collect events. The registry record does not report the adverse-event collection period, event definitions, severity grading procedures, or ascertainment methods.

The registry lists no top serious adverse-event terms. The count of 0 serious events should be interpreted alongside the number at risk and the limited enrollment, rather than as a guarantee of safety. The record does not provide a comparison between PET/CT and PET/MRI, nor does it identify separate safety results for each modality. It also does not report a detailed account of events by intervention component.

These figures describe what was entered in the registry record for this study group. They do not establish that the absence of recorded events applies to other populations, other imaging settings, or longer observation periods.

13. What the Result Does, and Does Not, Mean

The study addresses a focused imaging question in recurrent prostate carcinoma: how Ga68 PSMA uptake outside expected normal biodistribution can be characterized using PET/CT or PET/MRI. Its primary endpoint is an average SUVmax across 45 areas of high focal uptake, with the mediastinal blood pool used to determine average background. The record also identifies scan feasibility as a secondary outcome. Those details help define what the study set out to measure.

The registry record does not report the numerical primary endpoint result, its standard deviation, or a numerical feasibility result. Therefore, the data described in this record do not allow readers to assess the magnitude or variability of uptake, or the observed feasibility of the scans. They also do not allow an assessment of the precision of the endpoint estimate. The absence of a reported numerical result is not evidence that uptake was absent or that the imaging was infeasible; it means those outcomes are not reported in the registry record.

The study enrolled 10 participants and has a single-group design, without a randomized comparator or masking. It cannot establish a causal difference between PET/CT and PET/MRI, and the registry record does not report how participants were assigned to either modality. The design also does not compare either imaging approach with a separate control condition. No conclusion about relative diagnostic performance follows from the design information alone.

General explanation: feasibility studies can help describe whether a procedure can be carried out and identify practical issues for later research. They are not automatically designed or powered to establish diagnostic accuracy or clinical benefit. The registry record does not report a sample-size justification or a detailed statistical analysis plan, so the intended precision and inferential goals cannot be evaluated.

The appropriate interpretation is therefore limited to the recorded study structure, imaging procedure, endpoint definition, and safety counts. The record does not support conclusions about treatment effectiveness, diagnostic accuracy, comparative modality performance, or broader safety. Those questions require outcomes and methods that are not reported in the registry record.

14. Why This Trial Matters Statistically

This trial is statistically informative as an example of why an endpoint’s definition and unit of analysis matter as much as its label. The primary measure is an average of SUVmax values from 45 areas, while enrollment was 10 participants. Those are different units of information. If several regions come from the same participant, their measurements may be related, and uncertainty calculations should account for that dependence. The registry record does not explain how regions were distributed or how this structure was handled.

The study also illustrates the limits of interpreting a single-group feasibility design. With allocation listed as NA and no comparator group, the registry can describe the intended imaging procedure but cannot support a randomized comparison between PET/CT and PET/MRI. The absence of masking is relevant because image interpretation includes visual identification of regions with increased focal uptake. The record does not report reader procedures or whether interpretation was blinded to other information.

Another statistical lesson is the difference between a clearly defined outcome and a reported result. The record provides a detailed description of the primary measure, including the use of regions of interest and mediastinal blood pool background, but does not report the numerical mean or standard deviation. A method description alone cannot establish the observed size or precision of an effect.

Finally, planning illustrations should not be confused with the realized evidence from a feasibility study. The assumptions listed for such illustrations concern a two-arm calculation and do not match this single-group design. They are not observed power, and they cannot substitute for a reported endpoint estimate and its uncertainty. Together, these features make the study useful for discussing measurement, clustering, design limits, and reporting transparency, while keeping conclusions tied to what the registry record actually documents.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

Several trial-specific limitations constrain interpretation. Enrollment was 10, and the study was single-group, with allocation listed as NA and no masking. There is no randomized control group to support a comparative estimate, and the registry record does not report whether participants underwent PET/CT, PET/MRI, or both. How the imaging modality was selected is also not reported in the registry record.

The primary endpoint is based on 45 selected areas of high focal uptake, but the record does not report the number of areas contributed by each participant or the statistical handling of any within-participant clustering. The criteria for selecting regions are described only as visually appreciable increased focal uptake over background. Reader training, reproducibility, and adjudication procedures are not reported in the registry record. These missing details limit assessment of measurement consistency and potential selection effects.

The numerical primary endpoint result and its standard deviation are not reported in the registry record. A numerical feasibility result is not reported either. Although five outcome measures are listed, details for the other outcome measures are not reported in the registry record. There are no analysis entries, and the statistical analysis plan, sample-size justification, multiplicity procedures, analysis populations, and missing-data methods are not reported in the registry record.

Safety counts are recorded, but the adverse-event observation period, definitions, and ascertainment procedures are not reported in the registry record. The study’s completed status does not resolve these reporting gaps. These limitations mean that the registry record supports description of the design and measurement plan, but not a detailed assessment of endpoint magnitude, precision, comparative performance, or the generalizability of the safety findings.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: 68Ga-PSMA PET/CT or PET/MRI in Evaluating Patients With Recurrent Prostate Cancer — NCT02488070.
• Registry record last updated 2018-03-20; status last verified 2018-02.
• Results first posted 2017-03-14.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

NCT02488070 is a completed phase 1 and phase 2, single-group feasibility study sponsored by Stanford University. The registry lists enrollment of 10 and a study period from 2015-06 to primary completion in 2015-08. Participants received gallium Ga 68-labeled PSMA ligand Glu-urea-Lys(Ahx) intravenously, followed by PET/CT or PET/MRI approximately 45-60 minutes later.

The primary outcome was average SUVmax in 45 areas of high Ga68 PSMA uptake outside expected normal biodistribution, with mediastinal blood pool used to determine average background. The numerical result and standard deviation are not reported in the registry record. Scan feasibility was listed as a secondary outcome, but its result is not reported in the registry record. The record lists 0 serious adverse events, 0 other adverse events, and 0 deaths among 10 participants at risk in each adverse-event category. There are no analysis entries, and no randomized comparator.