Post Market Study Using the Xoft Axxent System: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Post Market Study Using the Xoft Axxent System (NCT01017549), a na na study. The primary outcome is Number of Participants With Delivery of 34 Gy in 10 Fractions.

2. Clinical Question

The registry describes a multi-center post-market study intended to compile performance and safety data on the Axxent System. This makes the record relevant to understanding what outcomes were intended to be tracked after the system entered clinical use. However, the record does not report an observed primary outcome result or an analysis of that result. The stated research question can therefore be identified from the endpoint definition, but its answer cannot be determined from the outcome information recorded.

The secondary outcome concerns serious adverse device-related events reported during the course of the study through 6 month follow-up. The posted safety figures list zero serious events among 44 at risk, alongside 22 with other adverse events among 44 at risk. These counts are descriptive registry figures; they do not establish how events were defined, assessed, or attributed beyond the wording recorded for the outcome.

3. Trial Design

This is a completed, single-group, multi-center post-market clinical study of the Axxent electronic brachytherapy system. The registry lists enrollment as 44 and the study status as completed. The recorded study start date is 2007-03-26, and the primary completion date is 2013-06-06. The phase is listed as NA. Xoft, Inc. is named as the sponsor.

The intervention is electronic brachytherapy (Axxent System), categorized as radiation. The arm description states that all patients were treated with FDA-cleared electronic brachytherapy treatment. The study has no separate control arm in the registry record. Allocation is listed as NA, masking as none, and the model as single group. Accordingly, the record describes treatment and outcomes in a treated group rather than a randomized, masked comparison between treatment strategies.

The primary outcome is the number of participants with delivery of 34 Gy in 10 fractions. Its timeframe is measured at the end of the 10th fraction, usually within 7 days. The outcome description defines successful delivery as a total 34 Gy in a total of 10 fractions, with 3.4 Gy per fraction. The outcome population is described as all patients treated were analyzed.

The secondary outcome concerns serious adverse device-related events reported during the course of the study through 6 month follow-up. The registry record does not report a detailed statistical analysis plan, eligibility criteria beyond the population named in the official title, or procedures for outcome assessment. Details about follow-up completeness and handling of participants with incomplete outcome information are also not reported in the registry record.

Because the design is single group, the posted outcomes can describe the treated group but do not supply a like-for-like control comparison. The registry explicitly identifies the study as not a randomized comparison. A difference between treatment strategies, or a causal effect relative to an alternative, cannot be estimated from this design alone.

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.

Before assignment: This was a single arm study, no randomization. Some patients consented but fell out of the study due to not meeting all eligibility (I/E) criteria after consenting to participation. 61 patients provided consent, 44 were treated.

Eligibility Through 6 Month Follow-up

Reasons for not completing this period:

One-year Follow-up

Reasons for not completing this period:

5 Year Follow-up

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: All patients treated were analyzed

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 Delivery of 34 Gy in 10 Fractions, measured over measured at end of 10th fraction, usually within 7 days.

The primary endpoint is a count: the number of participants with delivery of the specified radiation course. The registry defines successful delivery as a total dose of 34 Gy in 10 fractions, with 3.4 Gy per fraction. Assessment is scheduled at the end of the 10th fraction, usually within 7 days. The outcome description says all patients treated were analyzed.

This endpoint is used to describe treatment delivery and performance: it represents whether the stated course was delivered according to the registry definition. It is not an endpoint measuring tumor response, recurrence, survival, or comparative effectiveness. Those outcomes are not identified as the primary endpoint in the registry record.

For a binary outcome, each participant is classified according to whether the defined event occurred, and the group result is ordinarily expressed as a count and a proportion with an identified denominator. Here, the registry record identifies the outcome and its definition but does not report the observed count. The number of participants meeting the delivery definition is therefore not reported in the registry record. Without that result, the endpoint's observed frequency and its precision cannot be assessed from this record.

The clear dose-and-fraction definition makes the intended event interpretable, but does not by itself establish how adherence, deviations, or missing assessments were handled. Those details are not reported in the registry record. The outcome should therefore be read as a defined measure of treatment delivery, not as a complete account of every aspect of treatment performance.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a single-group study and records zero analyses. It provides outcome definitions and adverse event counts, but does not report a detailed statistical analysis plan. The explanations below are general statistical context, not a claim that the study used a particular method.

What does a count outcome tell readers?

The primary outcome is a participant count based on a binary definition: successful delivery means receiving 34 Gy in 10 fractions. For a binary outcome, each person is classified as meeting or not meeting the definition, and the count is interpreted in relation to an appropriate denominator. A count alone does not describe precision unless the denominator and an uncertainty estimate are also available. The registry record gives the endpoint definition and says all treated patients were analyzed, but does not report the observed primary count or an interval around it.

In general, a confidence interval describes uncertainty around an estimated quantity under stated assumptions. It is not a guarantee that the true value lies within a particular range, nor does it replace clinical interpretation. For a proportion, the interval's width depends in part on the amount of information available and on the observed event frequency. Since the primary result and its interval are not reported in the registry record, its precision cannot be evaluated.

Why does the design matter?

A single-group study can document how treatment was delivered and record events in the treated group. It does not, on its own, offer a concurrent untreated or alternative-treatment group for comparison. Random allocation, when used, helps make treatment groups comparable in expectation; this study is not recorded as randomized and has no comparator group. Consequently, an observed event count describes the group in the registry and cannot by itself identify a treatment effect relative to another strategy.

Masking is recorded as none. In general, masking can reduce the chance that knowledge of treatment influences some outcome assessments or reporting decisions. Whether this was relevant to particular assessments, and what steps were used to limit assessment bias, are not reported in the registry record. The endpoint is defined as delivery of a specified radiation course, but the record does not describe independent verification or adjudication.

What can the safety counts establish?

For serious adverse events, the record lists zero affected among 44 at risk; for other adverse events, it lists 22 affected among 44 at risk. These counts describe the recorded group and should be kept distinct from an estimate comparing groups. General statistical practice distinguishes serious from non-serious events because severity and clinical consequences differ, but the record does not provide the event terms or detailed classification rules. It also does not report a statistical comparison, uncertainty interval, or attribution assessment beyond the named serious adverse device-related outcome.

For event counts, extra variation may arise when participants have different underlying risks or follow-up experiences. In general, over-dispersion means that observed variation exceeds what a simple model assumes; a model that accounts for it can produce more realistic uncertainty estimates. The registry record does not report a model for event counts or a dispersion estimate, so it is not possible to say that an over-dispersion adjustment was performed or needed.

How should planning calculations be read?

General sample-size calculations ask how much information a future study would need to detect a specified effect under stated assumptions. The planning illustration associated with this record is described as being based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. It is explicitly a planning illustration, not the trial's own design. Its assumptions do not turn this single-group study into a randomized comparison, and a planning sample size is not observed power. Sample-size values and the effect estimate used for such calculations are not reported in the registry record summarized by these registry entries.

In general, power is a design property tied to a specified effect, model, and sample size. It is not a retrospective measure of whether a completed study produced a convincing result. A sample-size calculation based on an observed effect can be especially dependent on that estimate, and should be treated as planning context rather than independent confirmation. The registry record does not report a protocol-based sample-size justification or its assumptions.

Finally, the registry lists zero analyses. No adjustment strategy, missing-data method, interim analysis, or model specification is reported in the registry record. These absences limit reproducibility and make it inappropriate to attribute particular statistical procedures to the investigators.

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("Electronic Brachytherapy")
n      <- c(44)
events <- c(42)
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  Electronic Brachytherapy  44  42  95.5  84.5  99.4  84.9  98.7  84.9  98.6

11. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures: the primary treatment-delivery measure and a secondary measure concerning serious adverse device-related events through 6 month follow-up. It records zero analyses. No multiplicity procedure, testing hierarchy, or plan for interpreting several outcomes is reported in the registry record.

In general, when a study tests multiple outcomes, repeated testing can increase the chance of a false-positive finding if each result is treated as decisive. Prespecifying a primary endpoint and a testing strategy can clarify which result carries the main inferential emphasis. Here, the primary endpoint is identifiable from its title, but no inferential analysis is reported, so there is no reported family of statistical tests to evaluate or correction method to describe.

The primary outcome description states that all patients treated were analyzed. It does not report whether all treated participants had an observed endpoint assessment, how incomplete delivery information was classified, or whether any participants were excluded from the outcome result. The observed primary count is not reported in the registry record. Thus, the record does not allow an assessment of missing primary-outcome data or their possible influence.

The safety figures give 44 at risk for each adverse-event grouping. The registry does not explain follow-up completeness, event ascertainment procedures, or how participants with incomplete safety follow-up were handled. Deaths are recorded as null, which is not the same as a reported zero; a death count is not reported in the registry record. No missing-data method or analysis-population sensitivity analysis is reported.

In general, missingness matters when the probability that an outcome is unavailable is related to the outcome itself or to participant characteristics. Methods for addressing missing observations depend on the reasons and pattern of missingness and on assumptions that should be made explicit. The record does not provide enough information to assess those issues or identify a method used.

12. 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 4% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists serious adverse events for the Electronic Brachytherapy group as zero affected among 44 at risk. It lists other adverse events as 22 affected among 44 at risk. These are distinct categories in the record and should not be treated as interchangeable. The secondary outcome is described as serious adverse device-related events reported during the course of the study through 6 month follow-up.

The serious event count is a descriptive finding for the recorded group, not evidence from a comparison with another treatment. No serious-event terms are listed, so the registry record does not identify which specific events were assessed or provide event-level descriptions. Deaths are recorded as null; the record therefore does not report a death count rather than documenting a zero count.

The other adverse-event count indicates that 22 participants were recorded as affected, but the record does not give the event types, severity distribution, timing, recurrence, or attribution. It also does not provide an analysis of how complete follow-up was or how events were collected. The counts should be interpreted only within the recorded categories and their stated at-risk groups. They do not establish comparative safety, causation, or the absence of unreported events.

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

The registry record establishes the study's focus and design: a completed, single-group, multi-center post-market study of electronic brachytherapy with an endpoint defined by delivery of 34 Gy in 10 fractions. It also records adverse event counts for the treated group. These details make the intended treatment-delivery measure and the reported safety figures clear at a descriptive level.

The primary endpoint result itself is not reported in the registry record. Therefore, the central performance question—how many treated participants met the specified delivery definition—cannot be answered from the posted results. The record does not report an uncertainty interval, a statistical test, or an analysis estimate for that outcome. Completion of the study does not resolve this absence.

The safety results record zero serious adverse events among 44 at risk and 22 other adverse events among 44 at risk. These counts do not show how the experience would compare with another treatment, because there is no separate comparator and no randomized comparison. They also do not provide enough event detail to assess the nature or timing of the other adverse events. The null entry for deaths should not be read as a reported zero.

In general, an observed result is not the same as a causal treatment effect. A single-group design lacks a concurrent comparison that could help distinguish treatment effects from other explanations for outcomes. Nor can the stated dose-delivery endpoint be used to infer outcomes it does not measure, such as tumor response or survival. Those outcomes are not the primary endpoint described in this record.

The record consequently supports a limited reading: it documents what was intended to be measured, the study structure, and selected safety counts. It does not supply the primary outcome result or the comparative evidence needed to draw conclusions about relative benefit or risk. Any broader interpretation would go beyond the information reported in the registry record.

14. Why This Trial Matters Statistically

This study matters statistically because it illustrates the difference between a clearly defined endpoint and a reported endpoint result. The registry specifies a concrete treatment-delivery criterion: 34 Gy in 10 fractions, with 3.4 Gy per fraction. Yet the observed count of participants meeting that criterion is not reported in the registry record. Without the result, readers cannot estimate the endpoint frequency or assess its precision, regardless of how clearly the endpoint itself is worded.

The single-group design also sets an important boundary on interpretation. It can describe events in a treated group, but the absence of a comparator prevents a like-for-like estimate of how outcomes might differ under another treatment. The study is identified as post-market and intended to compile safety and performance data, but that purpose does not make descriptive observations equivalent to comparative evidence.

Safety reporting shows why counts need context. The record distinguishes serious adverse events from other adverse events, and gives separate affected and at-risk counts. It does not, however, report event terms or a death count. Clear categories are useful, while incomplete detail limits assessment of what the counts represent and how completely events were captured.

Finally, the record lists zero analyses. That makes the distinction between recorded outcomes and statistical inference especially important. Readers should not assume that an estimate, confidence interval, adjustment, or prespecified testing procedure exists when it is not reported. Taken together, the study is a useful example of how design, endpoint definitions, completeness of reporting, and analysis all shape what can be concluded from clinical data.

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 interpreting performance is that the registry record defines the primary endpoint but does not report its observed result. The delivery count, an uncertainty estimate, and any inferential analysis are not reported in the registry record. Consequently, neither the frequency of successful delivery nor its precision can be evaluated from the posted results.

The study is single group, with no comparator, and is not recorded as randomized. Outcomes in this design cannot establish differences relative to another treatment. Masking is recorded as none. The record does not describe methods for outcome verification, event adjudication, or steps to limit potential assessment or reporting bias.

Further details needed to evaluate the endpoint are not reported in the registry record: eligibility criteria beyond the population named in the official title, treatment deviations, completeness of endpoint assessment, and handling of incomplete observations. The primary outcome description says all patients treated were analyzed, but does not explain whether outcome data were available for everyone treated or how missing results were handled.

Safety interpretation is also limited. The record lists zero serious adverse events and 22 other adverse events among the stated at-risk groups, but does not report event terms, severity detail for other events, event timing, or the method for attributing events to the device. Deaths are null rather than a reported count. Follow-up completeness and ascertainment methods are not reported in the registry record.

Finally, no detailed statistical analysis plan, sample-size justification for the trial, interim-analysis plan, or multiplicity procedure is reported in the registry record. The planning illustration is explicitly not the trial's own design. These gaps limit reproducibility and prevent readers from judging whether analyses were prespecified or how uncertainty was intended to be quantified.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Post Market Study Using the Xoft Axxent System — NCT01017549.
• Registry record last updated 2020-08-13; status last verified 2020-08.
• Results first posted 2011-04-11.
• 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 record describes NCT01017549, Post Market Study Using the Xoft Axxent System, as a completed, multi-center, single-group post-market study sponsored by Xoft, Inc. Enrollment is listed as 44. The recorded start date is 2007-03-26, and the primary completion date is 2013-06-06. The study population is women with resected, early stage breast cancer, as named in the official title.

The intervention is electronic brachytherapy using the Axxent System. The primary endpoint counts participants with delivery of 34 Gy in 10 fractions, measured at the end of the 10th fraction, usually within 7 days. Its observed result is not reported in the registry record. The secondary outcome concerns serious adverse device-related events through 6 month follow-up.

The safety record lists zero serious adverse events among 44 at risk and 22 other adverse events among 44 at risk. Deaths are recorded as null. The registry lists two outcome measures and zero analyses. With no comparator group and no reported primary outcome result, the record supports description of the design and recorded safety counts, but not a comparative treatment-effect estimate.