Vessel Sparing Prostate Radiation Therapy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Vessel Sparing Prostate Radiation Therapy (NCT02958787), a na phase 2 study. The primary outcome is The Percentage of Patients Able to be Sexually Active With or Without the Use of Aids.

2. Clinical Question

The clinical rationale recorded for the study is that sexual function is an important quality-of-life concern for people considering prostate cancer treatment. The study description discusses a possible vascular mechanism of erectile dysfunction after radiation and proposes defining key vascular structures with MRI for treatment planning. That rationale explains the focus of the intervention and endpoint; it is not evidence that the planning approach preserved function.

The main question is therefore about the frequency of a specified patient-reported outcome after vessel-sparing radiation in the enrolled group. Because there is no concurrent comparator, the registry record cannot establish how that frequency differs from another treatment strategy. The outcome result itself is not reported in the registry record.

3. Trial Design

This is a phase 2, single-group study of radiation therapy for prostate cancer. The registry lists 135 participants as enrolled and the study status as completed. The sponsor is the University of Michigan Rogel Cancer Center. The recorded start is 2004-11, and the primary completion is 2009-10.

The intervention is described as vessel-sparing radiation therapy using MRI-based treatment planning to limit dose to critical erectile structures. The registry names the corpus cavernosum and internal pudendal artery as the structures of interest. It lists radiation therapy as the intervention. Allocation is recorded as not applicable, consistent with the single-group design, and masking is listed as none.

There is no randomized comparison or separate control arm in the record. Consequently, the design can describe an outcome among participants treated with this approach, but it does not by itself distinguish the intervention’s effects from other factors that may influence sexual activity or function. The registry’s design information does not specify a protocol-level comparison with another radiation-planning strategy.

The planned primary endpoint concerns erectile-function preservation five years from the end of radiation treatment. The record defines preservation as a score of 1 or 2 on a three-tier patient-reported questionnaire: sexually active without aids, sexually active with aids, or not sexually active with or without aids. The registry does not report how many participants completed this questionnaire at the specified time, the observed endpoint percentage, or a confidence interval.

The record lists one outcome measure and 0 analyses. It does not report a statistical analysis plan, sample-size justification, interim analysis plan, or detailed methods for follow-up. It also does not describe the enrolled participants’ baseline characteristics or explain how participants were selected for analysis. These gaps limit assessment of how completely the observed experience, if available elsewhere, would represent all enrolled participants.

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

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 The Percentage of Patients Able to be Sexually Active With or Without the Use of Aids, measured over 5 years from end of radiation treatment.

The primary endpoint is the percentage of patients able to be sexually active, with or without aids, five years from the end of radiation treatment. The registry defines erectile-function preservation as a score of 1 or 2 on a patient-reported, three-tier questionnaire. A score of 1 means sexually active without aids; a score of 2 means sexually active with aids; and a score of 3 means not sexually active with or without aids.

This definition combines the first two response categories into a binary outcome: sexually active with or without aids versus not sexually active. It therefore measures a particular patient-reported aspect of sexual function at a specified follow-up time. It does not separate unaided activity from activity with aids in the primary definition, and it is not a broader measure of every dimension of sexual function.

A percentage is useful for communicating how common the defined outcome is in the study group. A 95% confidence interval, the uncertainty measure listed for this endpoint, would describe the precision of an estimated percentage under the analysis assumptions. The registry record gives the endpoint definition and the intended timeframe, but does not report the observed percentage or its confidence interval. It also does not report the number of participants contributing responses at that timepoint or how missing responses were handled.

Because the endpoint is measured after treatment in a single group, it can describe the reported outcome among assessed participants if those results are available. Without a comparator, it cannot by itself quantify a difference attributable to vessel-sparing planning.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record identifies a binary percentage as the primary outcome: the percentage of patients able to be sexually active with or without aids at five years from the end of radiation treatment. The endpoint is derived from a three-tier patient-reported scale. The first two categories are counted as preservation, and the third is counted as no preservation under the study’s stated definition. The record lists a 95% confidence interval as the dispersion measure, but does not give the estimate or interval limits.

What does a percentage estimate describe?

In general, a percentage for a binary outcome describes the proportion of assessed participants whose responses fall into the defined category. Its interpretation depends on the outcome definition and on who contributes data. Here, the definition is stated, but the registry record does not report how many participants posted a response at the five-year timepoint or which analysis population was used. The enrolled total alone does not tell the reader how many participants were assessed for this outcome.

What does a confidence interval add?

In general, a confidence interval expresses statistical uncertainty around an estimate. A narrower interval indicates greater precision under the assumptions used to calculate it; a wider interval indicates less precision. The interval does not remove possible bias from missing responses, measurement choices, or the lack of a comparator. For this trial, the registry lists a 95% confidence interval as the endpoint’s dispersion measure but reports neither the percentage nor the interval. Precision therefore cannot be evaluated from the registry record.

What can a single-group design establish?

As a general matter, a single-group study can describe outcomes observed in the treated group. A concurrent comparison is needed to estimate a treatment contrast without relying on additional assumptions. This study is recorded as single-group, with allocation not applicable and no masking. There is no randomized control group in the registry record. An outcome percentage, had it been reported, would not on its own separate the contribution of the planning approach from other influences on the outcome.

The absence of masking is recorded, but the registry does not describe whether any outcome assessment procedures were blinded or independently reviewed. It would not be appropriate to infer such procedures. The registry also does not report the study’s statistical analysis plan, including any model specification, adjustment strategy, or details of the confidence-interval calculation.

How should planning illustrations be understood?

The planning assumptions describe an illustration based on an observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. Such illustrations concern hypothetical planning for a comparison; they do not describe this single-group study’s observed design. The assumptions state that the effect to detect is a stated fraction of the observed effect, but the registry record does not report numerical planning estimates or an observed primary effect from which to assess them.

Any sample-size illustration based on an observed effect is a planning calculation, not observed power and not evidence that the study had a particular probability of detecting an effect. The assumptions specify participants per arm for non-time-to-event outcomes. They do not turn this single-group study into a two-arm comparison, and they do not provide a sample-size justification for the trial. The trial’s own design justification is not reported in the registry record.

What is not available about the analysis?

The record lists one outcome measure and 0 analyses. It does not describe whether there were prespecified subgroup analyses, covariate adjustments, sensitivity analyses, interim looks, or a multiplicity procedure. It also does not explain how participants with missing questionnaires were treated. These details matter because analysis choices can affect the estimate and its uncertainty, particularly when not all enrolled participants contribute endpoint data.

General statistical interpretation should separate the endpoint’s definition, its estimated value, and the method used to quantify uncertainty. The definition is recorded; the value and confidence interval are not. The study design and planning assumptions are described at a high level, but detailed analysis methods are not reported in the registry record. Consequently, no recalculation or assessment of agreement with a sponsor analysis is possible from the posted endpoint information.

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("Intervention")
n      <- c(135)
events <- c(119)
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  Intervention  135  119  88.1  81.5  93.1  81.6  92.6  81.6  92.5

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure, identified as the primary endpoint, and 0 analyses. It does not report a multiplicity plan. In general, multiplicity concerns arise when several hypotheses or outcomes are tested and can affect the interpretation of statistical evidence. The record does not give enough detail to determine whether any additional outcomes or analyses were planned outside the listed information, so no claim about a correction procedure can be made.

Missing data are a separate concern. The registry record does not state how many participants completed the patient-reported questionnaire at five years, how many lacked a response, or why any responses might be missing. It also does not describe an imputation method, a complete-case approach, or a sensitivity analysis. The enrolled total of 135 does not establish the endpoint denominator.

Analysis populations are not specified. The record does not say whether the endpoint was to be analyzed among all enrolled participants, only those who received treatment, or only those with an available five-year assessment. The registry’s listing of 0 analyses leaves the analysis details unreported; it does not establish which analysis population would have been appropriate or used.

These omissions matter because the reported percentage and its confidence interval would depend on the participants included and the handling of missing responses. The primary result itself is not reported in the registry record, so it is not possible to evaluate how missingness, analysis choices, or multiplicity may have affected a numerical finding.

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 intervention group with 135 participants at risk for serious adverse events and 0 participants affected. For other adverse events, it likewise lists 135 at risk and 0 affected. The recorded death count is 0. No top serious adverse-event terms are listed.

These are the safety counts recorded for the group; they should be read as registry-reported figures, not as a complete description of every possible safety outcome. The record does not give additional detail about event definitions, collection procedures, reporting windows, or the extent of safety follow-up. It also does not provide a comparator group, so the counts cannot be used to contrast safety between treatment approaches.

A count of 0 in this listing does not supply information about whether every participant had complete safety assessment or whether the registry captures all events that may have occurred. Those details are not reported in the registry record. The figures should therefore be interpreted narrowly as the recorded adverse-event counts, rather than as proof that no adverse events occurred in any broader sense.

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

The registry record documents a study of MRI-based, vessel-sparing radiation planning for prostate cancer and defines a patient-reported endpoint related to sexual activity five years after treatment. It does not report the endpoint result. As a result, the record does not establish the percentage meeting the study’s definition of erectile-function preservation or the precision of that percentage.

The intervention’s rationale is to limit dose to the internal pudendal artery and corpus cavernosum during radiation planning. The registry describes these structures and the planning approach, but the rationale is not itself a measured outcome. An endpoint definition and an intervention objective cannot substitute for a reported result.

The study’s single-group design means that even a reported percentage would primarily describe outcomes in the group treated under this approach. Without a concurrent control group, it would not show how outcomes compare with another radiation-planning strategy or establish that the intervention caused any observed result. No treatment-effect comparison is reported.

The enrollment count and safety counts provide some context: 135 participants were enrolled, and the registry lists 0 participants affected by serious adverse events, 0 affected by other adverse events, and 0 deaths. Those safety figures do not answer the primary endpoint question. The record does not specify the safety reporting details needed to interpret the counts beyond their registry entries.

Overall, the registry record supports a description of the intended question, intervention, design, endpoint definition, and listed safety counts. It does not provide the primary outcome estimate, its confidence interval, endpoint completion information, or a comparative analysis. Therefore, it cannot support a conclusion about the frequency of the defined outcome or a causal conclusion about the planning approach.

14. Why This Trial Matters Statistically

This trial is statistically notable for the way its endpoint connects a planning objective with a patient-reported outcome. The intervention targets dose to named erectile structures, while the primary endpoint asks whether participants can be sexually active with or without aids at a defined follow-up time. Keeping those levels distinct is important: a treatment-planning rationale is not the same as an observed patient outcome.

The registry also illustrates why design determines the reach of an inference. A single-group study can describe the treated group, but it does not provide a concurrent treatment contrast. Even if the primary percentage were available, the design would not by itself show what outcome would have occurred under a different radiation-planning approach.

Precision is another central issue. The record identifies a 95% confidence interval as the endpoint’s uncertainty measure, yet gives neither the percentage nor the interval. Without both, readers cannot judge the result’s magnitude or statistical precision. The record also lacks the endpoint denominator and information about missing responses, which are needed to understand whom an estimate represents.

The planning assumptions describe a hypothetical equal-allocation, two-arm comparison and should not be confused with the recorded single-group design. Planning calculations are not observed power, and the registry does not report numerical planning estimates or a trial-specific sample-size justification.

Finally, the registry’s safety counts are distinct from the primary endpoint and do not resolve the missing efficacy result. Reading the record carefully means separating what is documented—the study structure, outcome definition, and counts—from what is not reported: the primary result, analysis details, and comparative evidence.

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.

The primary limitation for interpretation is that the registry record does not report the primary endpoint estimate or its 95% confidence interval. It therefore cannot answer the study’s stated question about the percentage able to be sexually active with or without aids at five years from the end of radiation treatment.

The study is recorded as single-group, without a randomized or concurrent control comparison. This limits causal interpretation: outcomes observed after treatment could not be contrasted within the study against outcomes under another planning approach. The record also lists no masking, and does not describe whether outcome collection or assessment used any additional safeguards.

Although 135 participants were enrolled, the number contributing a five-year endpoint response is not reported. The registry does not provide a participant flow account, reasons for missing questionnaire data, or methods for addressing missingness. The analysis population is also unspecified. These gaps make it impossible to assess how representative an endpoint estimate would be of the enrolled group.

The endpoint is based on a three-category patient-reported scale, with the first two categories combined for the primary definition. The record does not describe the questionnaire’s validation, administration procedures, or additional measures of sexual function. The outcome therefore should be understood only as defined in the registry, not as a comprehensive account of sexual function.

Other unreported details include the statistical analysis plan, sample-size justification, interim analyses, and any adjustment or sensitivity methods. The listed safety counts lack further detail about event definitions and reporting windows. These limitations are specific to the information recorded and prevent a fuller assessment of the study’s outcome, precision, and safety reporting.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Vessel Sparing Prostate Radiation Therapy — NCT02958787.
• Registry record last updated 2018-03-05; status last verified 2018-02.
• Results first posted 2018-03-05.
• 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 describes a completed phase 2, single-group study of vessel-sparing radiation therapy for prostate cancer. It lists 135 enrolled participants, no masking, and MRI-based planning intended to limit dose to the corpus cavernosum and internal pudendal artery. The primary endpoint is the percentage able to be sexually active with or without aids five years after radiation, based on a three-tier patient-reported scale.

The registry record does not report the primary endpoint result, its 95% confidence interval, the number assessed at follow-up, or detailed analysis methods. It lists 0 analyses. Safety entries list 0 participants affected by serious adverse events, 0 affected by other adverse events, and 0 deaths, with 135 at risk for each adverse-event category. No separate control group is recorded, so the study does not provide a like-for-like comparison.