MRI Guided SBRT for Localized Prostate Cancer: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for MRI Guided SBRT for Localized Prostate Cancer (NCT03778112), a randomized na study. The primary outcome is Number of Participants With Late Radiation Induced Genitourinary and Gastrointestinal Toxicity.

2. Clinical Question

3. Trial Design

This is a prospective, randomized, parallel study of MRI-guided radiotherapy for localized prostate cancer. The registry identifies masking as none and lists the phase as not applicable. Enrollment is recorded as 54. The sponsor is Rush University Medical Center. The recorded start date is 2016-05-23, and primary completion is listed as 2019-03. The study status is active, not recruiting; that status does not by itself establish whether all follow-up or analyses have been completed.

The treatment pathways are described according to mpMRI findings. Participants with a negative prostate scan were assigned to whole-prostate SBRT. Participants with a positive scan were assigned to IMRT to the prostate and seminal vesicles, followed by an SBRT boost to the whole prostate and a simultaneous integrated boost to MRI-defined intraprostatic lesions. The study summary describes differing fractionation approaches for the pathways. These are not presented as two treatments applied to the same MRI-defined population.

There is a design detail that the registry does not resolve. It labels the allocation randomized, while the arm descriptions link each radiotherapy regimen to the presence or absence of MRI-visible lesions. The randomization process, including what was randomized and whether randomization occurred within MRI-status groups, is not reported in the registry record. Therefore the two recorded arms should not automatically be interpreted as randomized treatment groups with comparable baseline characteristics.

The posted arm sizes are 4 for the negative-scan group and 50 for the positive-scan group. The record does not explain the imbalance, report baseline characteristics, or describe whether the enrollment figure and posted arm counts refer to the same analysis population. The primary outcome is set at 18 months, but the registry does not report the timing or completeness of participant-level follow-up. Three secondary outcomes are listed: acute radiation-induced genitourinary adverse events, biochemical recurrence, and disease-free survival.

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 Number of Participants With Late Radiation Induced Genitourinary and Gastrointestinal Toxicity, measured over 18 months.

The primary endpoint is the number of participants with late radiation-induced genitourinary and gastrointestinal toxicity. It is recorded as a participant count, with an 18-month timeframe. The endpoint description defines late toxicity as toxicity occurring more than nine months from the start of radiotherapy. The posted primary outcome counts are 4 for the negative mpMRI group and 50 for the positive mpMRI group, whose recorded group sizes are also 4 and 50.

In general, a toxicity endpoint is used to describe adverse effects observed after treatment, and a defined follow-up window helps specify which events count as late rather than acute. Genitourinary and gastrointestinal categories distinguish different types of reported toxicity. A participant count can communicate how many people were recorded as having an event, but interpretation depends on clear event definitions, ascertainment procedures, and a clear denominator.

For this record, the matching outcome counts and group sizes make the endpoint coding difficult to interpret as a toxicity result without further explanation. The registry does not clarify whether each participant was recorded as having the endpoint, whether the values represent something other than event counts, or whether the posted result was populated as intended. It also does not report the grading or detailed ascertainment rules for the primary outcome beyond the description of grade 3-5 toxicity and the timing definition. The record therefore identifies the intended clinical measure, but does not provide enough clarification to confidently interpret the posted counts as a comparison of late-toxicity occurrence between the groups.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a randomized, parallel study with no masking. In a parallel design, participants are followed in one assigned group rather than crossing between treatments. In general, random assignment can help balance measured and unmeasured participant characteristics across treatment groups when it is carried out as intended. Here, however, the record also describes treatment pathways based on whether the mpMRI scan identifies lesions. It does not explain what was randomized or how randomization was implemented. That missing detail matters when deciding whether the two MRI-status groups can be treated as randomized comparators.

What the endpoint count represents

The primary outcome is a participant count for late genitourinary and gastrointestinal toxicity, with an 18-month timeframe. The endpoint description says late toxicity occurs more than nine months after radiotherapy starts and specifies grade 3-5 toxicity. A count is a discrete outcome: it records how many participants meet the event definition. In general, understanding such a count requires knowing the event definition, the number of participants assessed, and how participants without complete follow-up were handled.

The record posts counts of 4 and 50 for groups with those same recorded sizes. Although the outcome is identified as a count of participants with an event, the registry does not explain whether these entries mean that every participant had the endpoint or whether the result values have another meaning. Nor does it say how the endpoint was assessed or whether any participants were excluded from assessment. The record also does not report a comparison estimate for this binary endpoint; it states that values are missing or not estimable for a two-arm comparison.

Why a comparison needs more than two counts

In general, a comparison between event counts needs clearly defined groups, an event definition applied consistently, and denominators representing participants at risk or assessed. A statistical method then quantifies uncertainty around the difference or another chosen contrast. For binary outcomes, methods may be selected according to the design, sample size, event frequency, and analysis objective. The registry does not report a method for the primary comparison, an estimate with uncertainty, or a p-value. It is not appropriate to infer those results from the posted counts, especially while their interpretation is unresolved.

In general, a confidence interval gives a range of estimates compatible with the observed data and assumptions of the method. It is not a guarantee that the true value lies within that range. A p-value describes how compatible observed data are with a specified null model; it does not measure the size or clinical importance of an effect. Neither quantity is available for the primary comparison in the record.

Planning illustrations and observed results

The record includes assumptions for sample-size planning illustrations based on the observed effect: a two-sided significance level of 0.05, equal allocation between arms, a normal approximation, and a target effect expressed as a fraction of the observed effect. For time-to-event outcomes, the stated planning convention uses the total number of events; for other outcomes it uses participants per arm. These are planning assumptions, not a report of the trial's own design justification. The registry does not report the protocol's sample-size justification.

In general, a sample-size illustration asks what sample size would be needed under stated assumptions to detect a particular effect with a chosen power. It is not observed power and does not show that the trial was designed around those assumptions. The equal-allocation assumption also differs from the posted arm sizes of 4 and 50. Because the observed endpoint counts and comparison are not interpretable as posted, the planning illustrations should not be treated as evidence about the strength or reliability of a treatment comparison.

Time-to-event outcomes and over-dispersion

Biochemical recurrence and disease-free survival are listed as secondary outcomes. In general, time-to-event analysis considers both whether an event occurred and how long participants were followed before an event or censoring. Censoring occurs when the event has not been observed by the last available follow-up or when observation ends for another reason. A valid interpretation depends on clear event definitions, follow-up information, and analysis methods. The registry does not report analysis results for these outcomes or explain censoring rules.

In general, over-dispersion means that variation in observed data exceeds what a chosen statistical model expects. It can affect uncertainty estimates when a model assumes less variability than is present. The primary outcome is a participant count, but no model or over-dispersion assessment is reported. The registry record therefore does not support a claim that over-dispersion was evaluated or that a particular adjustment was used.

What cannot be reconstructed

The record lists no analyses and does not provide a statistical analysis plan, an analysis population, missing-data methods, interim analyses, or a multiplicity procedure. Those details are not reported in the registry record. General statistical principles can explain why they matter, but cannot establish which procedures this study used. In particular, no unreported adjustment, model, imputation strategy, or randomization procedure can be inferred from the posted outcome labels or counts.

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("Negative mpMRI Prostate Scan", "Positive mpMRI Prostate Scan")
n      <- c(4, 50)
events <- c(4, 50)
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  Negative mpMRI Prostate Scan  4  4  100.0  39.8  100.0  51.0  100.0  47.8  99.5
ARM  Positive mpMRI Prostate Scan  50  50  100.0  92.9  100.0  92.9  100.0  93.0  100.0

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome and three secondary outcomes: acute radiation-induced genitourinary adverse events, biochemical recurrence, and disease-free survival. When several outcomes are examined, the possibility of chance findings across analyses can increase. In general, a prespecified hierarchy or multiplicity adjustment can help define how evidence across outcomes should be interpreted. The registry does not report whether outcomes were tested in a hierarchy, whether any multiplicity adjustment was planned, or how secondary outcomes were to be interpreted relative to the primary outcome.

The record lists zero analyses and does not provide inferential results for the primary comparison. It also does not report the statistical analysis plan, interim analyses, or an analysis population. The population used for each outcome, including whether all enrolled participants were included, is not reported in the registry record. The posted arm counts are 4 and 50, while the enrollment is 54, but the record does not explain the analysis flow or confirm that those figures describe the same population at the same stage of follow-up.

Missing-data handling is also not reported in the registry record. There is no account of participants lost to follow-up, unavailable toxicity assessments, or how incomplete outcome information was treated. In general, missingness can affect an estimate when participants with unavailable outcomes differ from those assessed. Without the amount, reasons, and handling of missing data, the possible effect on the reported endpoint cannot be assessed.

The primary endpoint has an 18-month timeframe and defines late toxicity as occurring more than nine months after radiotherapy starts. The registry does not give details of follow-up completeness through that period or explain whether the reported counts include only participants with an assessment at the specified time. These omissions, together with the unresolved meaning of counts that match group sizes, limit interpretation of both the primary and secondary outcomes.

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.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: other acute/late grade 1-2 gi/gu event (100.0%), grade late gu toxicity (4.0%).

The registry records serious adverse events affecting 4 of 4 participants in the negative mpMRI group and 50 of 50 participants in the positive mpMRI group. It separately records deaths of 0 in the negative-scan group and 4 in the positive-scan group. These are counts from distinct registry fields and should not be treated as interchangeable measures. The record does not explain how the serious-event counts relate to the primary late-toxicity endpoint or to the reported deaths.

The listed serious-event terms include “Other acute/late grade 1-2 GI/GU event” at 100.0% and “grade late GU toxicity” at 4.0%. The registry does not provide enough context to reconcile these terms and percentages with the serious-event group counts, or to establish their exact denominators and relationship to the primary outcome. The term describing grade 1-2 events also differs from the primary endpoint description of grade 3-5 toxicity.

In general, safety counts describe recorded events in the stated population; they do not by themselves establish that treatment caused an event. Interpretation depends on the event definitions, observation period, completeness of reporting, and whether counts refer to participants or events. The registry does not report those details sufficiently to resolve the apparent differences among its safety entries. The figures should therefore be read as posted registry counts, not as a complete comparative safety analysis.

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

The record identifies a prospective study of MRI-guided radiotherapy and describes different treatment pathways for negative and positive mpMRI findings. It also identifies late genitourinary and gastrointestinal toxicity as the primary outcome, with an 18-month timeframe and a definition of late toxicity as occurring more than nine months after radiotherapy begins. These details establish the intended clinical question and the broad structure of the study.

The posted primary outcome values are 4 and 50, matching the recorded group sizes of 4 and 50. The registry does not clarify whether these entries mean all participants had the defined toxicity or whether the values were populated or coded in another way. It also does not provide an estimable comparison, confidence interval, or p-value. As a result, these entries do not support a reliable estimate of how often late toxicity occurred or a conclusion about a difference between the MRI-status groups.

The record does not establish that the two groups are comparable as treatment groups. Although allocation is labeled randomized, the treatment descriptions follow MRI status, and the randomization process is not explained. MRI status and regimen are therefore linked in the registry description, and any group contrast could reflect differences beyond the radiotherapy regimen. The record does not provide information to disentangle those possibilities.

The serious adverse-event counts and death counts are recorded separately, but the record does not reconcile them with the primary endpoint or explain the listed adverse-event terms. They should not be used as substitutes for a clearly defined endpoint comparison. The secondary outcomes are listed without analysis results.

In general, a registry entry can describe study intent and record selected results, but it may not contain the detail needed to evaluate endpoint ascertainment, missing data, or statistical methods. This record does not report the analysis plan or enough information to resolve the count coding and group assignment questions. It therefore supports a careful description of what was registered, but not a claim that one regimen is safer or more effective than the other. It does not provide a basis for medical advice.

14. Why This Trial Matters Statistically

This study raises a useful statistical distinction between a prognostic classification and a treatment comparison. MRI findings define the two described pathways: a negative scan is linked to whole-prostate SBRT, while a positive scan is linked to IMRT followed by an MRI-guided SBRT boost. The registry also labels allocation randomized. When those design elements appear together, the randomization process needs to be clear before readers can decide whether a contrast between arms estimates a treatment effect or instead compares groups defined by MRI status.

The primary endpoint illustrates why result labels and coding need to be interpreted alongside denominators. The endpoint is a count of participants with late toxicity, yet the posted counts match the group sizes. Without a clear explanation, the figures cannot be confidently read as an event comparison. A registry can contain numerical results while still leaving uncertainty about what those numbers represent.

The safety entries reinforce the same point. Serious-event counts, death counts, and event-term percentages appear in the record, but their definitions and relationships are not reconciled. Statistical interpretation depends not only on calculations but also on knowing which participants and events a field represents. Clear endpoint definitions and transparent reporting of denominators are essential to turning counts into interpretable evidence.

Finally, the listed secondary outcomes and sample-size planning assumptions do not replace an analysis plan or reported results. Multiplicity, missing-data handling, analysis populations, and the randomization procedure are not reported. These omissions matter because they shape what conclusions an analysis could support. In general, transparent design and analysis reporting lets readers distinguish a descriptive registry entry from a well-defined comparative estimate. The unresolved details in this record make that distinction especially important.

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 main limitation for interpretation is the ambiguity in the primary outcome entries. The registry describes a count of participants with late grade 3-5 genitourinary and gastrointestinal toxicity, but posts values of 4 and 50 for groups of 4 and 50. It does not explain whether the values indicate events in all participants or reflect another coding or reporting issue. No estimable two-arm comparison is available in the record.

The relationship between randomization and MRI-guided treatment assignment is also unclear. The registry labels the study randomized, but describes each regimen according to whether MRI lesions were identified. It does not report the randomization process or explain whether treatment was randomized within MRI-status categories. Consequently, the two arms cannot be assumed to be directly comparable randomized treatment groups on the basis of the record alone.

The recorded arm sizes are highly uneven, but the registry does not explain how they arose, report baseline characteristics, or describe participant flow. It does not state whether all enrolled participants contributed to each outcome. The enrollment is 54, and the posted arm sizes are 4 and 50; the record does not provide additional information to reconcile those entries with follow-up or analysis populations.

Safety reporting lacks enough detail to connect the serious-event counts, deaths, and listed event terms to the primary toxicity endpoint. Event ascertainment, grading procedures, follow-up completeness, and missing-data handling are not reported. The registry also does not provide analyses for the secondary outcomes, a statistical analysis plan, or a multiplicity approach. These are limitations of the registry record and do not establish what may have been specified or analyzed elsewhere.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: MRI Guided SBRT for Localized Prostate Cancer — NCT03778112.
• Registry record last updated 2026-03-09; status last verified 2026-02.
• Results first posted 2023-02-14.
• 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

The registry describes a prospective, randomized, parallel study of mpMRI-guided radiotherapy for localized prostate cancer. Treatment pathways are linked to negative or positive mpMRI findings, and masking is listed as none. Enrollment is recorded as 54; the posted arm sizes are 4 and 50. The study is listed as active, not recruiting.

The primary outcome is the number of participants with late radiation-induced genitourinary and gastrointestinal toxicity at 18 months, with late toxicity defined as occurring more than nine months after radiotherapy begins. Posted primary outcome counts match the recorded arm sizes, but the registry does not explain how to interpret that coding. No two-arm comparison is estimable in the record, and zero analyses are listed.

Three secondary outcomes are recorded. The registry also posts serious-adverse-event counts and death counts, but does not reconcile these with the primary endpoint. The randomization process, analysis plan, missing-data handling, analysis populations, and multiplicity approach are not reported in the registry record.