BioProtect Balloon Implant™ Balloon System Pivotal Study BP-007: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for BioProtect Balloon Implant™ Balloon System Pivotal Study BP-007 (NCT03400150), a randomized na study. The primary outcome is Safety Endpoint: Number of Subjects in the Balloon and Control Groups With Rectal, Device or Procedure-related Grade > 1 AEs Within 6 Months of Procedure.

2. Clinical Question

3. Trial Design

The registry identifies this study as randomized, single-masked, and parallel-group. It lists the phase as NA and the status as completed. The enrollment field records 222. The primary outcome summaries use arm sizes of 139.0 for the balloon group and 78.0 for the control group; those outcome-analysis sizes do not match the enrollment field, and the registry record does not explain the difference. The adverse-event summaries use different at-risk counts, which should be read separately rather than treated as interchangeable denominators.

The intervention was a device: the BioProtect balloon system. The balloon arm is described as marking, balloon implantation, and IMRT; the control arm is described as marking and IMRT. The brief study description says the balloon is intended to hold the anterior rectal wall away from the prostate during radiotherapy and is absorbed by the body over time. These statements describe the device’s intended use, not an observed clinical outcome.

The listed primary endpoint is a participant count for rectal, device- or procedure-related Grade > 1 adverse events within 6 months of implantation. The outcome description frames the comparison as a non-inferiority question. The registry record does not report the trial’s non-inferiority margin, allocation ratio, masking details, randomization method, or original sample-size assumptions. It also does not explain which parties were masked. The record lists 2 outcome measures and 1 analysis, with no posted secondary outcomes. That limited registry information constrains interpretation of the analysis and the populations contributing to it.

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 Safety Endpoint: Number of Subjects in the Balloon and Control Groups With Rectal, Device or Procedure-related Grade > 1 AEs Within 6 Months of Procedure, measured over Within 6 months from balloon implantation.

The primary endpoint counts participants in each group who experienced a rectal, device- or procedure-related adverse event graded above 1 within 6 months of the procedure. It is a binary participant-level outcome: a participant either meets the endpoint definition or does not. The posted counts are 25.0 in the balloon group and 18.0 in the control group. The corresponding outcome-analysis group sizes are 139.0 and 78.0.

This endpoint is used to evaluate a safety question associated with the device and its implantation procedure. The registry specifically describes the intended comparison as non-inferiority in the occurrence of these adverse events. Non-inferiority analyses generally assess whether an intervention’s outcome is not worse than a comparator by more than a prespecified margin. That margin is essential to interpreting such a claim, but it is not reported in the registry record. The endpoint count alone therefore describes observed events; it does not establish whether a non-inferiority criterion was met.

The endpoint is narrower than all adverse events: it is restricted by the stated relationship to the rectum, device, or procedure, the grade threshold, and the 6-month timeframe. The record does not give a detailed event-adjudication definition or explain how participants with incomplete follow-up were handled.

7. Results Posted in the Registry

• Balloon Group: 18.0% (25/139) versus 23.1% (18/78) on control; risk difference -5.1 percentage points (95% CI -16.4 to 6.2), risk ratio 0.78 (0.45–1.34); unadjusted two-proportion z-test p = 0.367.

8. Statistical Interpretation

9. Statistical Methods Explained

For a binary endpoint, each participant is classified according to whether the defined event occurred during the stated follow-up period. The primary outcome is a count of participants with rectal, device- or procedure-related Grade > 1 adverse events within 6 months of implantation. The reported counts and analysis group sizes provide the basis for comparing the observed event proportions. The registry presents the comparison as a risk difference, with the balloon group contrasted against the control group.

A risk difference expresses the absolute separation between the event proportions in the groups. A negative value in this comparison indicates a lower observed proportion in the balloon group than in the control group; a positive value would indicate a higher observed proportion in the balloon group. The posted estimate is -0.051. This is a descriptive, unadjusted contrast and should not be read as an adjusted effect or as proof of causation beyond the randomized comparison. Random allocation supports a comparative design, but the registry record does not report details such as the allocation procedure or analysis adjustments.

A confidence interval gives a range of effect estimates compatible with the data under the statistical method used. The posted interval for the risk difference runs from -0.164 to 0.062. Its width reflects uncertainty around the point estimate. Because the interval includes the null value, the data do not pinpoint the direction of the underlying difference with high precision. The interval is not a range that contains a fixed proportion of individual participant outcomes, and it does not directly state the probability that the true effect lies within its limits.

The unadjusted p-value is 0.367. In general, a p-value evaluates how unusual data at least as discrepant as those observed would be if a specified null model and the analysis assumptions held. It does not measure the size or importance of an effect. It also does not replace the confidence interval, because the interval communicates the range of effect values compatible with the data. The registry record does not identify the test used to obtain the p-value or provide a complete statistical analysis plan.

The endpoint description uses the language of non-inferiority. In general, a non-inferiority analysis compares an estimated effect with a prespecified margin that defines the largest acceptable worsening. The margin, direction of the test, confidence-interval rule, and analysis population are needed to assess whether non-inferiority was demonstrated. The margin and decision procedure are not reported in the registry record. Consequently, the posted risk difference and p-value should not be substituted for a non-inferiority conclusion.

The study is listed as randomized, single-masked, and parallel-group. Randomization is intended to reduce systematic differences between groups at allocation; masking can reduce some forms of bias when participants or study personnel are unaware of assignment. The registry record does not say who was masked or how randomization was performed. These design labels provide context, but they do not disclose whether concealment, outcome assessment, or other procedures were implemented as planned.

The registry lists 1 analysis and 2 outcome measures, while no secondary outcomes are posted. It does not describe a multiplicity strategy. In general, testing several outcomes or comparisons can increase the chance of at least one apparently unusual result, and prespecified priorities or adjustment methods can help readers understand that risk. The available record does not indicate whether any such methods were used. Nor does it report how missing endpoint data, protocol deviations, or analysis populations were handled.

Simple recalculations from posted summary statistics can help readers understand the displayed contrast, but they cannot recover unreported design choices or replace the trial’s full analysis. The registry comparison is marked as having no discrepancy, so the concern about a conflicting sponsor analysis does not apply. The posted statistical details remain limited: the record does not supply a test specification, adjustment model, or a full account of participants included in the analysis.

10. Confidence Intervals and Precision

The risk-difference estimate is -0.051, and its confidence interval extends from -0.164 to 0.062. The estimate gives a single summary of the observed contrast, while the interval shows that substantial uncertainty remains about the size and direction of the underlying difference. Its limits include both negative and positive values, so the data are compatible with a lower event proportion in the balloon group as well as a higher one.

Confidence intervals are useful because they show more than whether a result crosses a decision threshold. In general, a narrower interval indicates greater precision about the effect estimate, while a wider interval indicates greater uncertainty. Precision depends on factors including the number of observations, event frequency, and the statistical method. The interval should be read in the context of the endpoint group sizes of 139.0 and 78.0, without assuming that the overall enrollment field describes the analyzed population.

The registry record does not report the confidence-interval method or the assumptions used to calculate it. It also does not report the non-inferiority margin, which would be required to judge the interval against the stated non-inferiority objective. Thus, the interval describes uncertainty around the posted risk difference but cannot independently establish non-inferiority. The unadjusted p-value of 0.367 offers a related summary of evidence under a null model, but it does not make the estimate more precise or resolve the missing margin.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size figures are planning illustrations based on the observed effect, not the trial’s own design assumptions. They use a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to the stated fraction of the observed effect. The registry record does not report the original assumptions used to plan this trial.

The displayed figures are participants per arm for 80% power and participants per arm for 90% power. In plain terms, the 80% column gives the planned number in each arm under the listed assumptions for an 80% chance of detecting the chosen effect if that effect is present; the 90% column does the same for a 90% chance. These are design illustrations, not statements about what the completed trial achieved. This is not observed power.

The rows vary the assumed effect: 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. As the target effect becomes smaller, more participants are required per arm under the same planning framework. The corresponding figures rise from 987 and 1,321 for planning at 100% of the observed effect, to 1,796 and 2,403 at 75%, and 4,129 and 5,527 at 50%, for the 80% and 90% power columns respectively. The observed effect is uncertain, as indicated by its confidence interval, so these illustrations should not be treated as a definitive estimate of a future trial’s needs. They also do not establish whether the original study was adequately planned for its non-inferiority objective.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.231; treatment proportion p₁ = 0.180; average p̄ = 0.205.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.5712 = 1.1196.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5701 = 0.4798.
4. n = (1.1196 + 0.4798)² / (-0.0509)² = 986.9, rounded up to 987 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.230769230769231                          # control proportion
p1 <- 0.179856115107914                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(3400150)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 987 (80% power), 1,321 (90% power)
 75% of observed effect: n per arm = 1,796 (80% power), 2,403 (90% power)
 50% of observed effect: n per arm = 4,129 (80% power), 5,527 (90% power)
power.prop.test: 986.9 
Simulated power at n = 987 per arm: 0.796 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry record lists 2 outcome measures and 1 analysis, and no secondary outcomes are posted. The primary endpoint is identified, but the record does not describe a hierarchy for outcomes, a multiplicity adjustment, or a prespecified strategy for interpreting multiple comparisons. In general, when several outcomes or tests are considered, the chance of a seemingly notable result can rise unless the analysis plan accounts for multiplicity. The available record is not sufficient to determine how this issue was handled.

Missing-data handling is not reported in the registry record. It does not state whether all participants were followed through the 6-month endpoint window, how incomplete follow-up was treated, or whether any imputation or sensitivity analyses were conducted. Without that information, readers cannot assess whether the posted counts reflect complete endpoint ascertainment or how missing outcomes might affect the comparison.

The analysis population is also not specified. The registry reports primary endpoint group sizes of 139.0 and 78.0, while the enrollment field lists 222. Adverse-event at-risk counts differ again. The record does not explain these differences or identify whether the primary comparison used an intention-to-treat, per-protocol, safety, or other population. These labels should not be assigned based on the available counts alone.

The non-inferiority objective makes analysis-population detail especially relevant, because different population definitions and missing-data assumptions can affect interpretation. The registry record does not report the original statistical analysis plan, the non-inferiority margin, or sensitivity analyses. Accordingly, neither multiplicity control nor robustness to missing outcomes can be evaluated from the posted information.

14. 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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: other (8.9%), pneumonia (2.5%), rectal bleeding (1.4%), acute urinary retention (1.3%), cerebral vascular retention (1.3%).

The adverse-event summary reports serious adverse events in 12 participants among 143 at risk in the balloon group and 10 participants among 79 at risk in the control group. For other adverse events, the corresponding figures are 108 among 143 and 60 among 79. The record also reports 1 death in the balloon group and 0 in the control group. These figures are separate from the primary endpoint counts and use the at-risk denominators listed in the adverse-event summary.

The serious-event terms listed with percentages include Other at 8.9%, Pneumonia at 2.5%, Rectal bleeding at 1.4%, Acute urinary retention at 1.3%, Cerebral vascular retention at 1.3%, and Rectal wall puncture at 0.7%. The record does not specify the denominator or counting convention for these term percentages in the posted summary. They should not be interpreted as the risk of each term without that context.

Serious adverse events, other adverse events, deaths, and the primary endpoint are different summaries. The registry record does not clarify whether event categories overlap or how events were attributed, beyond the primary endpoint’s stated relationship criteria. These figures describe the posted safety record; they do not by themselves establish comparative safety.

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

The posted primary result is a comparison of participant counts for a specified safety endpoint over a specified timeframe. The risk-difference estimate is -0.051, with a confidence interval from -0.164 to 0.062 and an unadjusted p-value of 0.367. The point estimate is in the direction of a lower observed endpoint proportion in the balloon group, but the interval spans possible differences in either direction and leaves substantial uncertainty about the effect.

The trial’s primary question is framed as non-inferiority, yet the registry record does not report the margin or decision rule needed to interpret that objective. The posted comparison therefore does not, on its own, demonstrate that non-inferiority was established. It also does not demonstrate that the groups are equivalent; failure to resolve a difference is not the same as proving equivalence.

The result is limited to rectal, device- or procedure-related Grade > 1 adverse events within 6 months of implantation as defined in the registry. It does not answer whether the device changes rectal radiation dose, all adverse events, longer-term outcomes, or outcomes beyond those posted. Although dose reduction is described as the device’s intent, the primary endpoint is not a radiation-dose endpoint.

The broader adverse-event summary gives additional descriptive safety information, but it has different denominators and does not resolve the primary endpoint’s limitations. The registry record does not explain how its enrollment and analysis counts relate, how missing data were handled, or which analysis population was used. These gaps limit the conclusions that can be drawn from the posted summary and should be considered alongside the numerical uncertainty.

16. Why This Trial Matters Statistically

This trial illustrates why an endpoint’s clinical framing and its statistical decision rule both matter. The primary question is explicitly described as non-inferiority, but a non-inferiority interpretation requires a prespecified margin and a stated method for comparing the estimate with that margin. Without those details, readers can understand the observed contrast but cannot determine whether the intended criterion was satisfied.

The result also shows the value of reporting an effect estimate with a confidence interval rather than relying on a p-value alone. The risk difference of -0.051 is accompanied by an interval from -0.164 to 0.062. That range makes the uncertainty visible and cautions against turning the direction of the point estimate into a definitive conclusion. The unadjusted p-value of 0.367 is relevant, but it does not describe the range of plausible effect sizes or establish equivalence.

Registry fields can differ in scope: enrollment, primary endpoint analysis sizes, and adverse-event at-risk counts are not the same entries in this record. Without an explanation of analysis populations and missing outcomes, it is difficult to reconcile them or assess the full flow of participants. Clear reporting of these details is important for interpreting randomized comparisons, especially when the endpoint is a safety outcome and the stated objective is non-inferiority.

Finally, the planning illustrations show how sample-size needs depend on the target effect under specified assumptions. They are not a substitute for the trial’s original design rationale, which is not reported in the registry record. Together, these features make the study useful for understanding the difference between observed results, statistical precision, and a formal conclusion tied to a prespecified clinical margin.

17. 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 registry record gives limited detail about the trial’s statistical design and conduct. It does not report the original sample-size assumptions, the non-inferiority margin, the randomization procedure, or who was masked. These omissions prevent a full assessment of the intended decision criteria and the protections against bias.

The enrollment field lists 222, while the primary endpoint analysis sizes are 139.0 and 78.0 and the adverse-event at-risk counts are 143 and 79. The record does not explain the differences among these entries. It also does not describe the analysis population, participant disposition, endpoint missingness, or handling of incomplete follow-up. These details are needed to judge how representative the posted comparisons are of the randomized groups.

The primary endpoint is defined by event type, grade, and timeframe, but the registry does not provide detailed adjudication procedures or an operational description of how relatedness was determined. The serious adverse-event term percentages have no stated denominator in the posted summary. These gaps limit interpretation of event classification and the separate safety summaries.

Only limited outcome and analysis information is posted: the record lists 2 outcome measures, 1 analysis, and no secondary outcomes. Multiplicity methods and sensitivity analyses are not reported. The results should therefore be interpreted as a registry-level summary rather than a complete account of the trial’s prespecified analysis and conduct.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: BioProtect Balloon Implant™ Balloon System Pivotal Study BP-007 — NCT03400150.
• Registry record last updated 2025-02-18; status last verified 2025-02.
• Results first posted 2024-10-30.
• 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.

21. Record Summary

NCT03400150 is the completed, randomized, single-masked, parallel-group BioProtect Balloon Implant Balloon System Pivotal Study BP-007 in prostate cancer. The balloon arm is described as marking, balloon implantation, and IMRT; the control arm as marking and IMRT. Enrollment is listed as 222.

The primary safety endpoint counts participants with rectal, device- or procedure-related Grade > 1 adverse events within 6 months of implantation. The posted counts are 25.0 in the balloon group and 18.0 in the control group. The risk difference is -0.051, with a confidence interval from -0.164 to 0.062 and an unadjusted p-value of 0.367. The registry describes the objective as non-inferiority but does not report the margin or decision rule. Analysis populations, missing-data methods, and reasons for differences in reported group sizes are not reported in the registry record.