Prospective Randomized Study of Accelerated Radiation Therapy (PRART): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Prospective Randomized Study of Accelerated Radiation Therapy (PRART) (NCT04175210), a randomized phase 3 study. The primary outcome is Proportion of Patients With Acute Toxicity Grade ≥ 2 on the 10-fraction Arm Compared to Proportion of Patients With Acute Toxicity Grade ≥ 2 on the 15-fraction Arm Evaluated up to 1-month Post-radiation Treatment.

2. Clinical Question

3. Trial Design

This is a phase 3, randomized, parallel-group trial with no masking reported. The registry lists enrollment as 397 and status as active, not recruiting. The study is sponsored by Weill Medical College of Cornell University. Its start date is 2019-11-21, and its primary completion date is 2025-07-15.

Participants are assigned to one of two whole breast radiotherapy schedules, each with a concomitant boost to the tumor bed. The standard arm uses 15 fractions over three weeks; the experimental arm uses 10 fractions over two weeks. The arm descriptions also specify the radiation amounts for the whole breast and tumor bed. Random assignment can support a comparison between assigned groups, but the registry record does not describe the randomization procedure, allocation concealment, or any stratification factors.

The primary outcome concerns acute toxicity of grade ≥ 2 according to the Common Terminology Criteria for Adverse Events, version 5.0, measured up to 1-month post-radiation treatment. The registry also lists outcomes concerning local breast cancer control, fibrosis, and breast cosmesis at later follow-up. Those outcomes are described at 2-3 Years and 5 Years post-radiation treatment. The registry record does not report results for these secondary outcomes.

The study title states that the comparison is intended to address non-inferiority for breast cosmesis and local control. The primary endpoint, however, is acute toxicity. The non-inferiority margin, the statistical analysis plan, and the planned approach to testing the primary endpoint are not reported in the registry record. The results should therefore be read as registry-posted outcome entries rather than as a complete account of the trial’s design or analysis.

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 Proportion of Patients With Acute Toxicity Grade ≥ 2 on the 10-fraction Arm Compared to Proportion of Patients With Acute Toxicity Grade ≥ 2 on the 15-fraction Arm Evaluated up to 1-month Post-radiation Treatment, measured over up to 1-month post-radiation treatment.

The primary endpoint is the proportion of participants with acute toxicity grade ≥ 2, compared between the 10-fraction and 15-fraction arms. The outcome is assessed up to 1-month post-radiation treatment. Toxicity is defined according to the Common Terminology Criteria for Adverse Events, version 5.0. A proportion represents the share of participants in an arm who meet the specified event definition; it is not a measure of how severe toxicity was beyond the grade threshold.

Binary outcomes such as this are used to describe how often a prespecified event occurs in each group. The grade threshold makes the endpoint a count of participants meeting a stated toxicity criterion, rather than a measure of every symptom or all grades of toxicity. The registry does not report a more detailed definition of which toxicities are included, how assessments were collected, or how missing toxicity observations were handled.

The posted arm-level entries give different proportions, with the 15-fraction arm higher than the 10-fraction arm. The separate comparison entry does not agree with those arm-level results: it records a zero risk difference, zero interval limits, and zero event counts. This inconsistency prevents a reliable interpretation of the comparison entry as an analysis of the stated primary endpoint. The registry record does not explain the discrepancy or provide a usable confidence interval for the arm-level contrast.

7. Results Posted in the Registry

• ARM 2 - 3200cGY and Boost to Tumor Bed of 4200cGY -10fractions: 0.0% (0/200) versus 0.0% (0/197) on control; risk difference 0.0 percentage points (95% CI 0.0 to 0.0); unadjusted two-proportion z-test p = n/a.

8. Statistical Interpretation

9. Statistical Methods Explained

What does a proportion measure?

For a binary endpoint, each participant is classified according to whether the event definition is met. A proportion describes the share of participants in an arm who meet that definition. Here, the event is acute toxicity grade ≥ 2 within the stated assessment period. The measure does not convey the full distribution of toxicity grades, the timing of individual events within the assessment period, or the experience of participants without recorded assessments.

Comparing proportions is a natural way to describe a binary endpoint. A risk difference expresses the contrast as the proportion in one group minus the proportion in another, with the direction depending on which group is placed first. This is a general explanation of the statistical measure, not a claim that a valid risk difference is available for this trial. The registry’s arm-level values and comparison entry are inconsistent, and the registry does not explain how the comparison entry was generated.

Why does randomization matter?

Randomization assigns participants to study groups using a chance-based process. As a general statistical principle, it aims to reduce systematic differences between groups at assignment, including differences that may not be measured. A randomized design can make a treatment comparison more credible than an uncontrolled comparison, provided that the assignment, follow-up, outcome measurement, and analysis are carried out and reported appropriately.

The registry identifies this trial as randomized and parallel-group, and reports no masking. It does not describe the allocation procedure, concealment, stratification, or analysis population. The absence of masking means the record does not indicate that participants or study personnel were masked to the assigned schedule; further details about who knew the assignments are not reported in the registry record. These omissions limit what can be assessed about implementation and potential influences on outcome assessment.

What is a confidence interval for?

In general, a confidence interval describes the statistical uncertainty around an estimate under the assumptions of the analysis. A narrower interval indicates greater precision, while a wider interval indicates that a broader range of values remains compatible with the data and method. An interval is not a guarantee that the true value lies within its limits, and it does not by itself determine whether a difference is clinically important.

No usable confidence interval for the primary arm-level comparison is reported in the registry record. The comparison entry gives zero for both interval limits, but those values accompany zero event counts and a zero risk difference that conflict with the arm-level proportions. They therefore cannot be interpreted as a meaningful uncertainty interval for the posted arm results.

How does non-inferiority differ from a usual difference test?

As a general concept, a non-inferiority trial asks whether an intervention is no worse than a comparator by more than a prespecified margin. The margin sets the largest difference that the study will regard as compatible with non-inferiority under its decision rule. This requires an explicit margin and an analysis that compares the estimate and its uncertainty with that margin. The trial title describes the study as non-inferiority, but the margin, analysis plan, and decision rule are not reported in the registry record. The primary endpoint listed in the record is acute toxicity, while the title emphasizes breast cosmesis and local control.

What can be concluded from the posted entries?

The primary outcome type is binary, and the registry lists an arm denominator and a proportion for each schedule. Those entries can be described as recorded, but the conflicting comparison result prevents a sound interpretation of the between-arm estimate. The record does not provide an analysis explanation, a coherent interval, or a reported p-value that can be used to assess uncertainty. No inferential result should be reconstructed from the arm proportions alone in the absence of an appropriate analysis record.

General statistical practice also distinguishes a descriptive result from an adjusted or protocol-specified analysis. A descriptive proportion summarizes the recorded observations in an arm. An adjusted analysis may account for prespecified characteristics or design features, but neither an adjustment approach nor adjusted estimates are reported in the registry record. It is therefore not possible to determine whether the posted arm values represent the planned analysis, an unadjusted summary, or a particular analysis population.

Over-dispersion is a concern mainly for outcomes that are counts, when variability exceeds what a simple count model expects. It is not the central issue for this primary binary proportion. For a binary endpoint, the key interpretive needs are a clear event definition, denominators, a valid comparison estimate, and an uncertainty interval. The posted record supplies arm-level proportions and denominators but has a contradictory comparison entry and no usable interval. This limits statistical interpretation regardless of the randomized design.

10. Confidence Intervals and Precision

Precision concerns how narrowly the data and analysis locate an effect estimate. A confidence interval is a standard way to display that uncertainty: it gives a range of estimates compatible with the data and the method under stated assumptions. The interval is especially important when a trial is framed as non-inferiority, because the estimate must be considered against a prespecified margin. The margin for this trial is not reported in the registry record.

The registry provides no usable confidence interval for the primary comparison. Its comparison entry lists a zero risk difference and zero lower and upper limits, together with zero event counts. These entries do not accord with the nonzero arm-level proportions, and the record does not explain the mismatch. The zero limits cannot be taken as evidence of exceptional precision. They indicate a reporting inconsistency, not a supported uncertainty assessment.

The arm-level entries include denominators of 197 for the 15-fraction arm and 200 for the 10-fraction arm, but no arm-level confidence intervals are reported. Without an interval or a valid comparison analysis, readers cannot assess the precision of the difference from the registry record. The record also does not report missing-outcome handling, which matters because the denominator used in an analysis can affect the interpretation of a proportion.

The posted values are therefore best treated as descriptive entries with unresolved uncertainty, rather than as a precise estimate of the treatment contrast. The registry record does not report a statistical conclusion about whether the schedules meet a non-inferiority criterion.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists the primary acute-toxicity outcome and six secondary outcomes. The secondary outcomes concern local breast cancer control, fibrosis, and breast cosmesis at the stated follow-up periods. When a study evaluates multiple outcomes or time points, general statistical practice considers how the collection of analyses affects interpretation; repeated testing can increase the chance of apparently notable findings. The registry record does not report a multiplicity adjustment or a strategy for prioritizing secondary analyses.

The record lists no analyses. It does not report an analysis plan, a prespecified hierarchy among outcomes, or whether any secondary outcomes are intended to be confirmatory or descriptive. The title’s non-inferiority framing refers to breast cosmesis and local control, while the listed primary endpoint is acute toxicity. How these aims relate within the planned analysis is not reported in the registry record.

Missing data and analysis populations are also not described. The record does not state how missing toxicity assessments, withdrawals, or participants without follow-up would be handled. It does not identify whether the primary comparison would use an intention-to-treat, per-protocol, or other population. These details are particularly relevant to non-inferiority interpretation, but no specific approach can be inferred from the registry entry.

The arm denominators are reported for the primary endpoint, but they do not explain how the denominators were selected or whether they include all participants assigned to each arm. The registry record also does not report sensitivity analyses for missing outcomes. Consequently, the available entries do not allow readers to assess the effects of missingness, population definitions, or multiplicity on any inferential result.

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

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: left breast hematoma evacuation (0.5%), rash with itching skin reaction (0.5%), dyspnea (0.5%).

The registry reports serious adverse events by study arm. For the 15-fraction arm, 2 serious adverse events are listed among 197 participants at risk; for the 10-fraction arm, 1 is listed among 200 participants at risk. No deaths are listed in either arm. These are counts and denominators as recorded, not rates calculated for comparison. The registry does not provide a statistical comparison or confidence intervals for these safety entries.

The record also lists other adverse events: 32 among 197 participants at risk in the 15-fraction arm, and 19 among 200 participants at risk in the 10-fraction arm. Those entries are separate from the serious adverse event counts and should not be combined with them. The record does not provide further detail about the definitions, timing, duration, or attribution of the other adverse events.

Three serious adverse event terms are listed with a frequency of 0.5% each: Left Breast Hematoma evacuation, Rash with itching skin reaction, and Dyspnea. The record does not assign these terms to a particular study arm, so they cannot be used to compare the arms. Adverse-event counts describe what was recorded in the registry; they do not by themselves establish whether an event was caused by treatment or whether groups differ reliably.

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

The registry record documents a randomized comparison of two radiotherapy schedules and posts arm-level results for acute toxicity grade ≥ 2. The recorded proportions differ, with the 15-fraction arm higher than the 10-fraction arm. This is a descriptive observation about the posted arm entries. It is not a complete inferential comparison, because the separate comparison fields report zeros that conflict with those arm-level values.

The record does not provide a usable confidence interval, a valid reported comparison estimate, or a reported analysis result that resolves this inconsistency. It also does not state the non-inferiority margin or decision rule. Therefore, the entries do not establish whether the experimental schedule satisfies the trial’s stated non-inferiority aim. They also do not support a conclusion about the precision or statistical significance of the primary contrast.

The acute-toxicity endpoint is not interchangeable with the trial’s listed outcomes for local control, fibrosis, and breast cosmesis. Those secondary outcomes have specified follow-up periods, but their results are not reported in the registry record. The primary outcome entries alone do not answer questions about those outcomes or about longer-term effects.

The posted adverse-event counts provide additional descriptive safety information, but they have no reported comparative analysis. The registry does not provide enough detail to determine event attribution, completeness of reporting, or how missing observations were handled. These limitations mean the record should be interpreted as an incomplete statistical account, rather than as a definitive assessment of the relative schedules.

In general, a trial result is strongest when the endpoint definition, analysis population, comparison estimate, uncertainty interval, and prespecified decision rule are all clear. Several of those elements are absent or internally inconsistent in this registry record. The record can identify what was planned and what values were posted, but it does not support a broad conclusion about treatment performance.

14. Why This Trial Matters Statistically

This trial is statistically notable because it compares two randomized schedules while posing questions about both acute toxicity and longer-term breast outcomes. Randomization provides a framework for comparing assigned groups, and the registry identifies a clear primary outcome based on an adverse-event grade threshold. The record also names later outcomes involving local control, fibrosis, and breast cosmesis.

The contrast between the stated non-inferiority aim and the primary endpoint listed in the registry makes clarity of the analysis especially important. Non-inferiority depends on a stated margin and a comparison that accounts for uncertainty. Neither the margin nor a usable interval for the primary outcome is reported. The record’s arm-level entries and comparison entry also conflict, so readers cannot rely on the comparison fields to quantify the contrast.

These issues illustrate a general statistical point: a randomized design does not, by itself, make every posted result interpretable. Complete reporting of definitions, denominators, analysis populations, estimates, and uncertainty is needed to connect the design to a sound conclusion. Reporting secondary outcomes and follow-up results is also essential when the trial’s aims include longer-term clinical outcomes.

The registry record therefore offers a useful example of why descriptive results, inferential results, and non-inferiority conclusions must be distinguished. It records a planned randomized comparison and arm-level outcome values, but the absent analysis details and inconsistent comparison entry leave important statistical questions unanswered.

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.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

Several limitations arise from the registry record itself. The primary arm-level proportions are not accompanied by confidence intervals, while the separate comparison entry reports zero for the risk difference, interval limits, event counts, and probability-related fields. Those zero entries conflict with the arm-level values, and the record does not explain the discrepancy. As a result, the primary comparison cannot be interpreted as a coherent inferential result.

The non-inferiority margin, analysis plan, and decision rule are not reported in the registry record. Nor does the record specify allocation procedures, concealment, stratification, analysis population, or how missing outcomes were handled. These omissions limit assessment of both the design implementation and the statistical analysis. The record lists six secondary outcomes but does not report their results or a multiplicity strategy.

The primary endpoint is acute toxicity assessed up to 1-month post-radiation treatment, while the trial title also emphasizes breast cosmesis and local control. Results for the listed longer-term outcomes are not reported in the registry record. The posted safety counts also lack a comparative analysis and do not assign the listed serious adverse event terms to an arm.

These limitations concern what can be concluded from the registry record; they do not establish that the trial lacked a protocol or analyses outside the record. Details not included in the registry entry are not reported in the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Prospective Randomized Study of Accelerated Radiation Therapy (PRART) — NCT04175210.
• Registry record last updated 2026-05-07; status last verified 2026-05.
• Results first posted 2026-05-07.
• 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 phase 3 randomized, parallel-group study with no masking reported, comparing whole breast radiotherapy over 15 fractions in three weeks with treatment over 10 fractions in two weeks. The listed primary endpoint is acute toxicity grade ≥ 2 up to 1-month post-radiation treatment. The record lists enrollment as 397 and status as active, not recruiting.

Arm-level primary-outcome proportions are posted, but the separate comparison entry reports zero values that conflict with those arm-level results. No usable confidence interval, non-inferiority margin, analysis plan, or secondary-outcome results are reported in the registry record. The posted information therefore supports a limited descriptive reading, not a definitive statistical conclusion about the comparison.