HDR Brachytherapy 68-Ga-RM2 PET, 68-Ga-PSMA-11 PET &Multi Parametric MRI in Prostate Cancer: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for HDR Brachytherapy 68-Ga-RM2 PET, 68-Ga-PSMA-11 PET &Multi Parametric MRI in Prostate Cancer (NCT04264208), a randomized phase 2 study. The primary outcome is Number of Participants With Successful Assessment of PET Based PC Lesions.

2. Clinical Question

The study is registered as a phase 2 randomized crossover trial with no masking. Its brief summary describes assessment of response to HDR local therapy, while the primary outcome description focuses on lesion detection over multi-parametric MRI. These are related but distinct aims: the outcome posted in the record is a count of participants with successful lesion assessment, not a reported measure of treatment response. The record does not report a definition of successful assessment, a diagnostic accuracy measure, or an inferential analysis for the primary question.

3. Trial Design

The registry record describes a randomized, unmasked, crossover phase 2 study. Enrollment is listed as 4, and the status is terminated. The two intervention sequences differ in which PET/MRI is performed first: 68Ga-RM2 followed by 68Ga-PSMA-11, or 68Ga-PSMA-11 followed by 68Ga-RM2. In both descriptions, the second scan is scheduled within 2 weeks of the first. The record does not report why the study was terminated.

The primary outcome timeframe is Day 1 for the first scan and 2 weeks for the second scan relative to baseline. The first scan was approximately 2 months prior to HDR treatment. This timing places the imaging assessment in the pre-treatment setting, although the brief summary also describes a broader interest in assessing response to local therapy.

A crossover design gives each participant the opportunity to undergo both imaging approaches, while randomizing the sequence can help separate modality comparisons from order effects. That is a general description of the design, not evidence that all planned scans were completed or that order effects were analyzed in this trial. The registry record does not report the number of participants completing each sequence, scan completion, withdrawals, or the analysis population.

The outcome record posts a count of 2 for 68Ga-RM2 PET/MRI and a count of 2 for 68Ga-PSMA-11 PET/MRI. It does not provide a formal comparison between these counts. Because this is a crossover study, the arm labels should be understood in the context of the imaging sequences and outcome reporting, not as proof that participants in one group received only one modality. Details of the analysis accounting for paired observations are not reported in the registry record.

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.

Before assignment: 4 participants signed consent and three participants were randomized to treatment.

Pre-HDR Scan Sequence

HDR Treatment at 2 Months

Post-HDR Scan Sequence at 10 Months

Analysis population for the primary outcome, as defined in the registry: Participants with pre HDR treatment scan data

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 Number of Participants With Successful Assessment of PET Based PC Lesions, measured over Day 1 (first scan) and 2 weeks (second scan) relative to baseline. First scan was approximately 2 months prior to HDR treatment.

The primary endpoint is the number of participants with successful assessment of PET-based prostate cancer lesions. Its stated purpose is to assess whether 68Ga-RM2 and 68Ga-PSMA-11 PET/MRI can detect additional cancers over multi-parametric MRI. The outcome description says lesion detection is assessed by the two PET scans, and the population is described as participants with pre-HDR treatment scan data.

A participant count is a direct summary of how many participants met the endpoint definition. It is not, by itself, a measure of diagnostic accuracy. To interpret such a count as evidence about detection performance, readers would need a clear definition of successful assessment and a basis for determining whether lesions were truly present, such as a stated reference standard. The registry record does not report those details, nor does it post sensitivity, specificity, predictive values, or a comparison against biopsy.

The record lists a value of 2 for each imaging modality. These counts do not establish that the modalities performed equally: the record does not report the endpoint denominator for each modality alongside the count, an uncertainty interval, or a statistical test. Nor do the counts show whether an individual participant had a successful assessment under both methods. Thus, the endpoint is relevant to the study’s lesion-detection question, but the posted summary is too limited to quantify comparative performance.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical interpretation depends on matching the method to both the study design and the form of the outcome. The primary outcome is a participant count, and the registry classifies the endpoint as binary, with the meaning described as participants with an event. In general, a binary endpoint records whether each participant meets a defined condition. A count of participants meeting that condition can be informative, but it needs a denominator and an unambiguous endpoint definition to be interpreted as a frequency.

What does a confidence interval add?

In general, a confidence interval expresses the uncertainty around an estimated quantity under a specified statistical model. It helps distinguish a precisely estimated result from one that is compatible with a wide range of values. The registry record does not post a confidence interval for the primary endpoint. With only the reported counts, readers cannot assess the range of plausible values for either modality from the posted results.

Why does the crossover design matter?

In general, a crossover study compares measurements made under different conditions within the same participants. Such observations are often related: some participants may be more readily assessed than others regardless of imaging modality. A paired analysis accounts for this within-participant relationship, whereas an analysis treating all observations as independent can misrepresent uncertainty. Randomizing the order of the two modalities can help address order effects, but it does not remove the need to account for paired outcomes.

The registry record describes two possible scan sequences and a second scan within 2 weeks of the first. It does not report whether all scans were completed, how the sequence assignment was handled in the analysis, or whether the primary comparison used paired data. It also does not report participant-level outcomes or a cross-tabulation of success under each modality. Without those details, the statistical method used to compare the imaging approaches cannot be reconstructed from the posted results.

What can be inferred from the counts?

The posted endpoint values are counts rather than modeled effect estimates. A count does not describe the chance of success unless the corresponding denominator is known and the endpoint definition is clear. The record lists an n of 2 for each modality, but it does not explain how the endpoint count and those entries relate to the randomized sequences, scan completion, or the full enrolled population. It would therefore be inappropriate to calculate rates, contrasts, ratios, or uncertainty measures from the posted summary.

For a two-arm binary endpoint, a comparison typically needs a clearly defined event, denominators for each comparison group, and a method suited to the allocation and observation structure. In this crossover setting, the participant is the unit that links results from the two scans. A valid comparison could depend on how many participants meet the endpoint under both methods, under only one method, or under neither. Those paired outcome patterns are not reported. The record states that values are missing or not estimable for a two-arm comparison, and no analyses are posted.

What is a p-value?

In general, a p-value measures how incompatible the observed data are with a specified null hypothesis under a chosen model. It is not the probability that the null hypothesis is true and does not measure the clinical importance of a result. No p-value is posted for the primary comparison, so the record does not support a formal significance judgment. A p-value would not replace the need to understand the effect estimate, uncertainty, outcome definition, and study design.

How should planning calculations be read?

In general, sample-size calculations describe how many observations a future study might need under stated assumptions about an effect, significance level, allocation, and statistical model. They are planning illustrations, not observed power and not evidence that the completed study achieved a particular probability of detecting an effect. The registry’s stated planning assumptions use a two-sided significance level of 0.05, equal allocation, a normal approximation, and effects defined as fractions of the observed effect. The record does not report a design justification or an inferential primary comparison. Because the comparison is not estimable from the posted summary, the planning assumptions should not be treated as evidence of the study’s intended or achieved precision.

In general, a statistical plan would specify the primary estimand, analysis population, handling of missing scans, treatment of paired observations, and any adjustment for multiple outcomes. Those details determine how a result is calculated and what population it describes. The statistical plan is not reported in the registry record. Therefore, the posted counts should be read as descriptive outcome entries rather than as the result of a documented comparative analysis.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("68Ga-RM2 PET MRI", "68Ga-PSMA-11 PET MRI")
n      <- c(2, 2)
events <- c(2, 2)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  68Ga-RM2 PET MRI  2  2  100.0  15.8  100.0  34.2  100.0  29.2  99.2
ARM  68Ga-PSMA-11 PET MRI  2  2  100.0  15.8  100.0  34.2  100.0  29.2  99.2

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists 3 outcome measures, but no secondary outcome results are posted. It reports zero analyses. The record does not explain whether a hierarchy of outcomes was planned, whether any multiplicity adjustment was intended, or how the primary endpoint was selected for confirmatory interpretation. These details are not reported in the registry record.

Multiplicity arises when several outcomes, comparisons, or repeated tests are examined. In general, testing many hypotheses can increase the chance of finding an apparently notable result by chance. Methods such as prespecifying a hierarchy or adjusting statistical thresholds can address this issue, but the appropriate approach depends on the study’s aims and analysis plan. The registry record does not report a multiplicity strategy, so no claim about control of false-positive findings can be made.

The posted primary outcome includes counts for both PET/MRI modalities, but the record does not report endpoint denominators, participant-level paired outcomes, or an analysis population. It does not state how missing scans or incomplete outcome assessments were handled. The stated outcome population is participants with pre-HDR treatment scan data, but that description does not establish which participants had usable data for every assessment. Missing-data methods are not reported in the registry record.

In general, missing observations can affect both the estimated result and its uncertainty, particularly when completion is related to participant characteristics or scan findings. A complete-case analysis, imputation, or another approach makes different assumptions; none should be attributed to this study without documentation. The record also does not report whether the analysis followed randomized sequence assignment or included all participants who began imaging. The analysis populations and any exclusions are therefore unclear.

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 adverse-event record lists zero serious adverse events among 3 participants at risk in the 68Ga-RM2 PET/MRI group and zero among 3 at risk in the 68Ga-PSMA-11 PET/MRI group. It also lists zero other adverse events in each group and zero deaths in each group. These figures describe what is posted in the registry record; they do not establish that no adverse events occurred outside the recorded categories or reporting period.

The safety denominators differ from the enrollment figure of 4, and the registry record does not explain the relationship between them. Because the study is a crossover trial, participants may be represented under both imaging procedures; the adverse-event entries should not be added to infer a number of distinct participants. The record does not report the safety follow-up period, event collection procedures, attribution to a procedure or agent, or reasons for any difference between the at-risk counts and enrollment.

No serious adverse-event terms are listed. A zero count is not evidence that risk is absent, particularly when the posted safety experience is limited and the observation details are not reported. These entries are descriptive and should not be used to compare safety between the imaging approaches.

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

The posted result is a pair of equal participant counts: 2 for successful PET-based lesion assessment with 68Ga-RM2 PET/MRI and 2 with 68Ga-PSMA-11 PET/MRI. The registry record does not report a statistical comparison, uncertainty interval, or diagnostic accuracy estimate. The counts therefore describe the registry entries but do not establish equal performance, superiority, or equivalence.

The trial’s stated clinical question concerns whether PET/MRI can detect additional prostate cancer lesions over multi-parametric MRI. The posted endpoint does not report how many additional lesions were found, whether findings were confirmed, or how PET-based assessment compared with MRI or biopsy. The record also does not give a definition of successful assessment. As a result, the counts cannot be interpreted as a direct estimate of how often either modality correctly detects cancer.

The crossover design makes participant-level correspondence important. The registry record describes both imaging procedures and two possible orders, but does not provide paired outcomes or state how those observations were analyzed. The reported counts cannot show whether the same participants had successful assessment with both methods or whether results differed within participants.

The study is listed as terminated, but the reason is not reported in the registry record. The posted enrollment and outcome information should be viewed in that context without assuming why the study ended or whether termination affected the results. The record does not report a statistical analysis plan, the handling of missing data, or the analysis populations.

In practical statistical terms, the evidence available in the registry is descriptive and limited. It supports reporting the posted counts and the absence of a posted comparative analysis. It does not support a treatment recommendation or a conclusion about clinical benefit. More complete outcome definitions, denominators, paired results, reference-standard information, and an analysis plan would be needed to assess the comparative diagnostic question with precision.

14. Why This Trial Matters Statistically

This study is statistically notable because it combines a randomized crossover design with imaging assessments that may be observed within the same participant. That structure can make within-person comparisons useful, but it also requires methods that respect the pairing. Reporting only modality-specific counts does not show how the paired results align or differ. The absence of a reported paired analysis leaves the central comparison unresolved.

The primary endpoint is a count of participants meeting a success criterion, while the stated scientific interest is detection of additional cancers over multi-parametric MRI. Those are not interchangeable summaries. A participant-level success count needs a clearly stated definition and denominator; a diagnostic-performance question may also require a reference standard and lesion-level information. The registry record does not report those details, so the endpoint’s relationship to the broader scientific question is difficult to evaluate.

The small enrollment listed in the record and the terminated status make transparent reporting especially important. The record posts counts for the imaging procedures but no inferential analyses, no uncertainty estimates, and no explanation for termination. This is not evidence that a particular result is true or false; it limits how confidently readers can characterize the findings.

The registry also illustrates the distinction between descriptive outcome reporting and a prespecified statistical analysis. Counts can convey what was entered as an outcome, but they do not substitute for denominators, paired outcome patterns, a missing-data strategy, and a documented analysis population. Those elements are necessary to understand what comparison was estimated and how much uncertainty surrounds it.

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 details needed to interpret the primary outcome are not reported in the registry record. The endpoint is described as successful assessment of PET-based prostate cancer lesions, but the criteria for success are not specified. The record does not explain how additional cancers were established, whether a reference standard was used, or how PET findings were compared with multi-parametric MRI or biopsy.

The posted counts do not include an inferential comparison, confidence interval, or p-value. The record does not show participant-level paired outcomes, so it is not possible to determine how assessments under the two imaging procedures corresponded within participants. Although the randomized sequences are described, completion by sequence and the handling of order are not reported.

The enrollment figure is 4, while the outcome entries list an n of 2 for each modality and the safety entries list 3 participants at risk for each. The registry record does not explain these different figures or identify the denominators used for the endpoint. They should not be combined to infer participant totals or completion rates. The missing-data approach and analysis populations are also not reported.

The study is marked terminated, but the reason for termination is not reported in the registry record. There is no posted statistical analysis, and the registry does not report a statistical plan, interim analyses, or sample-size justification. These omissions prevent assessment of whether the reported outcome reflects the intended analysis or how much precision was planned.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: HDR Brachytherapy 68-Ga-RM2 PET, 68-Ga-PSMA-11 PET &Multi Parametric MRI in Prostate Cancer — NCT04264208.
• Registry record last updated 2024-02-01; status last verified 2024-01.
• Results first posted 2024-02-01.
• 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

The registry record describes a phase 2 randomized, unmasked crossover study of 68Ga-RM2 and 68Ga-PSMA-11 PET/MRI in prostate cancer. Enrollment is listed as 4, and the study status is terminated. Participants were assigned to one of two imaging sequences, with the second scan described as occurring within 2 weeks of the first.

The primary outcome counts participants with successful assessment of PET-based prostate cancer lesions. The posted counts are 2 for each imaging modality. No statistical analyses are posted, and the record does not report a comparative estimate, uncertainty interval, endpoint denominator, or paired participant-level results. The reason for termination and the statistical analysis plan are not reported in the registry record.

The adverse-event entries list zero serious events, zero other events, and zero deaths in each modality group, with 3 participants at risk in each. The safety follow-up details are not reported. Overall, the registry provides descriptive counts but not enough information to assess comparative diagnostic performance or precision.