Trental & Vitamin E for Radiation-Induced Fibrosis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Trental & Vitamin E for Radiation-Induced Fibrosis (NCT00583700), a randomized phase 2 study. The primary outcome is Subjective, Objective, Management, and Analytic (SOMA) Score.

2. Clinical Question

3. Trial Design

The registry describes a randomized, phase 2, parallel-group study with no masking. It lists an enrollment of 54 and identifies the University of Iowa as the sponsor. The study status is completed. Its recorded start was 2003-02, and its primary completion was 2010-05. These are registry dates; the record does not describe the timing or conduct of recruitment in further detail.

One arm received watchful waiting, described as the study control. The other received pentoxifylline and vitamin E in combination. The registry describes the research aim as determining whether the combination prevents radiation fibrosis among women receiving radiation for definitive breast cancer management. It does not provide more detailed eligibility criteria, treatment schedules, adherence information, or allocation procedures in the record.

The primary outcome was the mean SOMA score at 18-month post-treatment follow-up. The registry reports arm-level means and standard deviations and a mean-difference comparison. The primary-outcome population description says all enrolled participants were evaluated for SOMA scores, while also noting that the numbers varied with compliance with follow-up appointments. The posted arm results include 27 participants in the control arm and 25 in the intervention arm.

Tissue compliance, measured in millimeters, was listed as a secondary outcome at 18 months post-treatment. Its posted arm results include 24 participants in the control arm and 23 in the intervention arm. The record also contains adverse-event counts for the control and intervention groups. The protocol's original sample-size rationale, detailed statistical analysis plan, and procedures for handling missing 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.

Overall Study

Analysis population for the primary outcome, as defined in the registry: All participants enrolled in the study were evaluated for SOMA scores. Numbers varied by study participants compliance with follow-up appointments.

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 Subjective, Objective, Management, and Analytic (SOMA) Score, measured over 18 month post-treatment.

The primary endpoint is the composite Subjective, Objective, Management, and Analytic (SOMA) score at the 18-month post-treatment visit. It is expressed in units on a scale. The registry states that zero is ideal and represents no treatment-related side effects at the study visit, while the maximum possible score is 45. A lower score therefore corresponds to a result closer to the registry's stated ideal on this scale.

A composite score can summarize several aspects of a condition or its effects in one measure. That can make it useful for an overall comparison, but interpretation depends on how the components are defined, scored, and combined. The registry record does not give further detail about the component-level scoring rules or how the composite is constructed. It also does not report a threshold for a change considered clinically important.

The primary endpoint is reported as a mean, with a standard deviation describing variability among the observations within each arm. The registry says all enrolled participants were evaluated for SOMA scores, but the number with outcome data varied according to compliance with follow-up appointments. The reported means therefore describe the observations available for each arm, while the record does not explain how missing follow-up scores were handled in the analysis.

7. Results Posted in the Registry

• Intervention: Pentoxifylline & Vitamin E: mean 1.00 versus 1.59 on control; difference -0.59 (95% CI -1.33 to 0.15), standardized effect d = -0.43; z-test p = 0.119.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Tissue Compliance

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Intervention: Pentoxifylline & Vitamin E: mean 0.88 versus 2.10 on control; difference -1.22 (95% CI -2.40 to -0.04), standardized effect d = -0.59; z-test p = 0.042.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Intervention: Pentoxifylline & Vitamin E than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The registry lists one secondary endpoint, tissue compliance, measured in millimeters at 18 months post-treatment. Its arm summaries and unadjusted comparison are distinct from the primary SOMA outcome. As the outcomes measure different aspects of the study, their results need not point to the same statistical conclusion or carry the same interpretation. The registry does not define the clinical direction of a favorable tissue-compliance result, nor does it report an interpretation threshold for the measure.

The secondary comparison's unadjusted p-value is 0.042, while the primary comparison's unadjusted p-value is 0.119. These are separate tests of separate outcomes. The secondary result should not be used to overwrite the primary result, and a nominal finding on a secondary endpoint is not, by itself, confirmation of the primary hypothesis. The record does not state a hierarchical testing plan or a multiplicity correction.

When multiple outcomes are assessed, the chance of seeing at least one apparently unusual result can increase. This is a general statistical concern: the more comparisons considered, the more cautious interpretation of unadjusted p-values should be. The record lists two outcome measures and one secondary endpoint, but does not explain whether additional outcomes or tests were planned, or how the posted outcomes were selected for reporting. That absence limits the strength of conclusions drawn from the secondary finding.

The numbers of observations also differ by endpoint. The registry does not explain the reasons for these differences or report methods to address missing outcome data. Therefore, the overall pattern is best understood as one primary result with uncertainty and a secondary result that warrants cautious, exploratory interpretation. Neither the differences between the p-values nor the endpoint pattern establishes why the results differ.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Tissue Compliance

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous and is summarized using a mean and standard deviation for each arm. A mean describes the average observed score. A standard deviation describes how dispersed individual scores are around that average; it is not the uncertainty in the estimated arm mean. In these results, the posted standard deviations are 1.53 for control and 1.19 for the intervention arm. The registry's outcome description says zero is the ideal SOMA score and 45 is the maximum.

What does the mean difference represent?

The comparison is reported as the intervention mean minus the control mean. The posted estimate is -0.59, consistent with the reported arm means of 1.0 and 1.59. The negative sign means the observed intervention-arm mean was lower on the scale. Since the scale's stated ideal is zero, the direction is toward a lower score, but the estimate alone does not establish that the groups differ beyond sampling uncertainty or that the intervention caused the difference.

A mean difference keeps the comparison in the original units of the outcome, making its direction and scale directly interpretable. A standardized effect can instead express a difference relative to variability, but the registry does not make that the primary comparison. The posted mean difference and confidence interval are the central quantities for interpreting the primary result.

What does a confidence interval add?

A confidence interval gives a range of estimates compatible with the observed data under the assumptions used for the calculation. It communicates uncertainty around the estimated mean difference. For the primary outcome, the interval includes zero, the value corresponding to no difference between the arm means. The unadjusted p-value is 0.119. Together, these do not provide strong evidence of a between-arm difference by conventional significance testing, but they do not prove that there is no difference.

A p-value describes how surprising data at least as incompatible with a null hypothesis would be if that hypothesis and the test's assumptions were true. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of a difference. The registry labels the primary comparison's p-value as unadjusted. The record does not report a multiplicity adjustment or a detailed testing plan.

Why can the number of observations matter?

The primary outcome description says that all enrolled participants were evaluated, but that the numbers varied with compliance with follow-up appointments. The posted primary results list 27 control participants and 25 intervention participants. A mean and standard deviation calculated from observed follow-up scores summarize those observations; they do not, by themselves, show whether participants without a score differ from those with one. The registry record does not report imputation, a missing-data model, or sensitivity analyses. Consequently, the impact of incomplete follow-up on the comparison cannot be assessed from the record.

For a continuous outcome, variation among observations and the number with outcome data both affect the precision of a mean comparison. Greater variability or fewer observed scores generally makes an estimate less precise, all else being equal. This is a general statistical principle, not a claim about the cause of the observed uncertainty in this study. The posted confidence interval is the direct summary of precision for the comparison.

How should the secondary comparison be viewed?

Tissue compliance is also summarized as a mean with a standard deviation, and its comparison is a mean difference. The posted unadjusted p-value is 0.042. A result below a conventional 0.05 threshold is often described as nominally statistically significant when considered by itself. But a secondary endpoint is one of multiple opportunities to observe a result, and the record does not report any adjustment for that. General statistical practice treats unadjusted secondary findings as less conclusive when there are several outcomes or tests, particularly when their prespecification and testing hierarchy are not documented.

The study's original statistical analysis plan, its sample-size justification, and any interim-analysis procedures are not reported in the registry record. As a result, the posted summaries do not establish whether the analysis followed an original plan or whether any additional analyses were conducted but not reported. No recalculated analysis is needed to interpret the comparisons: the record presents the arm summaries and mean-difference estimates, and no discrepancy is flagged.

11. Confidence Intervals and Precision

Precision concerns how narrowly the data estimate a between-arm difference. The primary mean-difference estimate is -0.59, and its confidence interval crosses zero. Thus, the posted data are compatible with a range of possible differences, including no difference. The interval's lower endpoint is -1.332; the upper endpoint is positive. This uncertainty is important: the direction of the point estimate alone does not settle whether the groups differ.

The p-value for the primary comparison is 0.119, and it is unadjusted. A p-value is not a measure of precision by itself, and it does not say how likely the observed effect is to be real. The confidence interval is more informative about the range of differences compatible with the data under the analysis assumptions. The record does not report a clinically important difference threshold, so it is not possible to use the interval to determine whether the data exclude effects that would be important to patients or clinicians.

The secondary tissue-compliance comparison has a posted mean difference of -1.22 millimeters and a confidence interval that lies below zero. Its unadjusted p-value is 0.042. This interval describes uncertainty for that outcome's mean difference, but it does not account for testing multiple outcomes. The direction's practical meaning is not specified in the registry record.

In general, confidence intervals become narrower when estimates are more precise and wider when data provide less information. The registry notes that follow-up compliance affected the number of SOMA observations, and the posted outcome counts are not identical across endpoints. The record does not provide enough detail to assess how missing observations, trial conduct, or analysis choices affected interval coverage. Confidence intervals should therefore be read as uncertainty summaries under the reported analysis, not as guarantees about the true difference.

12. 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 display is a planning illustration based on the observed effect, not the trial's original design assumptions. The original design assumptions and sample-size justification are not reported in the registry record. For these continuous outcomes, the displayed figures are participants per arm, rather than total events. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is a stated fraction of the observed effect.

The 80% power column gives the illustrative number of participants per arm for a design with an 80% chance of detecting the specified effect if that effect were the true effect and the planning assumptions held. The 90% power column uses a higher chance of detection, which generally requires a larger planned sample for the same effect. These are planning calculations, not observed power.

Rows that use smaller fractions of the observed effect ask what would be needed to detect a more modest difference. Smaller effects are harder to distinguish from random variation, so the illustration requires more participants per arm for those rows. For example, the primary-outcome planning display gives 86 participants per arm for 80% power when planning for 100% of the observed effect, compared with 343 participants per arm when planning for 50% of the observed effect. These numbers are not evidence that the trial had those group sizes or that a future study should use them without further design work.

The figures depend on assumptions that may not match the trial's actual design, outcome variability, missingness, or analysis plan. They are best read as conditional planning illustrations tied to the posted effect estimate. The registry does not report the trial's own target sample size rationale, so the display cannot establish whether the original study was adequately sized for its primary question.

13. 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, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -0.590; pooled standard deviation σ = 1.377.
2. n = 2 × (1.96 + 0.842)² × 1.377² / -0.590² = 85.5, rounded up to 86 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
delta <- -0.59                      # observed difference in means
sigma <- 1.37731477883598                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^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 (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(583700)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 86 (80% power), 115 (90% power)
 75% of observed effect: n per arm = 153 (80% power), 204 (90% power)
 50% of observed effect: n per arm = 343 (80% power), 459 (90% power)
power.t.test: 86.5 
Simulated power at n = 86 per arm: 0.791 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-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.

14. Multiplicity, Missing Data and Analysis Populations

The registry record does not report whether the study used a multiplicity adjustment, a prespecified hierarchy of endpoints, or a formal plan for interpreting secondary outcomes. It lists a primary SOMA score and a secondary tissue-compliance measure, and the posted comparison p-values are unadjusted. When more than one statistical test is considered, unadjusted p-values do not account for the increased opportunity to observe a nominally notable result by chance. This is why the secondary comparison should carry less weight than a result from a clearly prespecified primary analysis.

The record also does not report a detailed statistical analysis plan. Information about covariate adjustment, assumptions checks, handling of outliers, or alternate analyses is not reported in the registry record. No reported analyses are listed for the secondary outcome. Without those details, it is not possible to determine whether the posted comparisons were the only analyses contemplated or how they relate to a prespecified plan.

Missing outcome data are relevant because the primary outcome description says that the number of participants with SOMA scores varied according to follow-up appointment compliance. The record provides arm-specific counts for the posted endpoint but does not report a missing-data method, the characteristics of participants without observed scores, or sensitivity analyses. It is therefore not possible to assess from the registry record whether missing follow-up could have changed the estimated comparison.

The registry says all enrolled participants were evaluated for SOMA scores, but that statement is accompanied by the qualification about varying follow-up counts. It does not give enough detail to identify a specific analysis population beyond the posted observations. The record does not state whether the primary analysis followed an intention-to-treat principle or how participants with incomplete follow-up were included. These omissions do not invalidate the posted summaries, but they limit assessment of robustness and the scope of conclusions that can be drawn.

15. Safety Results

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

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

The adverse-event record lists 27 participants at risk in the control group and 27 at risk in the intervention group for both serious and other adverse events. It reports zero serious adverse events and zero other adverse events in each group. No serious adverse-event terms are listed. Death counts are not reported in the registry record.

These are reported counts for the groups and categories in the registry record. They should not be interpreted as proof that no events occurred outside the recorded reporting framework, or as a comparison establishing equal safety. The adverse-event group counts also differ from the posted primary-outcome counts: the registry lists 27 control and 25 intervention participants for the primary endpoint. The record does not explain the difference in denominators, provide event definitions or follow-up details, or describe how adverse events were collected. The counts therefore provide limited information for comparing safety between arms.

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

The primary comparison describes the observed mean SOMA score in the two trial arms at 18-month post-treatment follow-up. The intervention-arm mean was lower than the control-arm mean, and the reported mean difference was -0.59. Since the registry identifies zero as the ideal SOMA score, the point estimate is in the direction of a lower score in the intervention arm. But the confidence interval crosses zero and the unadjusted p-value is 0.119. The posted primary result therefore does not establish a clear difference between the groups.

That does not mean the study proves there is no effect. A nonsignificant result can reflect uncertainty about the size or direction of a difference, and the confidence interval includes both negative and positive values. The registry does not report a threshold for a clinically important difference, so the practical importance of the estimated difference cannot be established from these results alone.

The tissue-compliance result is a secondary comparison. It has a nominally notable unadjusted p-value, but the registry does not report multiplicity handling, a testing hierarchy, or the clinical interpretation of the measure's direction. It is therefore not a substitute for the primary result and should be interpreted cautiously.

These results apply to the outcomes and observations reported in this completed randomized phase 2 study. The registry describes the population as women treated with radiation for definitive breast cancer management, but it does not provide detailed eligibility criteria, treatment schedules, or subgroup results. Generalization beyond the studied setting cannot be assessed from the posted record. The result also does not establish causation beyond what the design and analysis support, and the registry's limited detail on missing follow-up and analysis methods leaves important uncertainty unresolved.

In short, the record gives an estimate and its uncertainty, not a definitive verdict. It does not establish that the combination prevents radiation fibrosis, and it does not establish that the combination has no effect. The appropriate reading is a primary comparison with an uncertain difference and a secondary result that requires cautious interpretation.

17. Why This Trial Matters Statistically

This trial illustrates why the estimate, interval, and endpoint hierarchy all matter when interpreting clinical results. The primary mean difference points toward a lower SOMA score in the intervention arm, but its confidence interval includes zero and the unadjusted p-value is 0.119. Reading only the direction of the estimate would overstate what the data establish; reading only the p-value would conceal the range of plausible differences. The confidence interval makes the uncertainty more visible.

It also illustrates the distinction between a primary outcome and a secondary outcome. The tissue-compliance comparison has a different unadjusted p-value, but it addresses a different measure and the registry does not report multiplicity procedures. Treating the secondary result as decisive evidence would ignore the possibility of chance findings across multiple comparisons and the absent analysis-plan detail.

Follow-up is another statistical issue with direct interpretive importance. The registry explicitly notes that SOMA outcome counts varied with appointment compliance. That makes transparent reporting of missing-data methods important, yet such methods are not reported in the registry record. Readers cannot determine whether the analysis accounts for missing outcomes or whether sensitivity analyses support the posted comparison.

Finally, the sample-size illustration is useful for understanding how planning requirements depend on the effect to be detected, but it is not a retrospective measure of success. The original design assumptions are not reported, and the illustration is based on the observed effect under stated planning assumptions. The distinction between a planning calculation and observed trial evidence is central to responsible statistical interpretation.

18. 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 contains limited detail about who was eligible, how participants were assigned, and how the interventions were delivered. It identifies randomization, parallel groups, and no masking, but does not describe the randomization method, concealment procedures, treatment schedules, or adherence. These details are important for judging the risk of bias and the applicability of the results.

The primary outcome description notes variation in SOMA follow-up counts due to compliance with appointments. The record does not explain the missing-data process, compare participants with and without follow-up scores, or report sensitivity analyses. The primary endpoint's posted counts are 27 in the control arm and 25 in the intervention arm; tissue-compliance counts are 24 and 23. The registry does not explain these differing counts.

The record does not report an original sample-size justification, detailed analysis plan, interim analyses, missing-data methods, multiplicity adjustment, or clinically important difference threshold. Nor does it give further detail on SOMA component scoring or the interpretation of the tissue-compliance measure. The secondary comparison is reported without an analysis hierarchy or multiplicity context.

The safety information is also limited to the posted event counts. Event definitions, collection procedures, follow-up periods for safety, and death counts are not reported in the registry record. These limitations constrain interpretation of efficacy, safety, and generalizability. They should be understood as limitations of the information available in the record, not as evidence that the unreported procedures or analyses did not occur.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Trental & Vitamin E for Radiation-Induced Fibrosis — NCT00583700.
• Registry record last updated 2013-01-29; status last verified 2012-10.
• Results first posted 2013-01-29.
• 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.

22. Record Summary

NCT00583700 is a completed randomized phase 2 study sponsored by the University of Iowa. It used a parallel-group design with no masking reported and compared watchful waiting with combined pentoxifylline and vitamin E. The registry lists enrollment of 54 and describes the population as women treated with radiation for definitive breast cancer management.

The primary endpoint was mean SOMA score at 18-month post-treatment follow-up, with zero described as ideal. The posted mean difference was -0.59, with a confidence interval crossing zero and an unadjusted p-value of 0.119. Tissue compliance was listed as a secondary outcome. Its unadjusted comparison should be interpreted cautiously because multiplicity handling is not reported. The registry notes variable primary-outcome follow-up counts and does not report missing-data methods or the trial's original sample-size rationale.