The Gamma Pod: A Clinical Feasibility Study Device GCC 1202: The Gamma Pod: A Clinical Feasibility Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Gamma Pod: A Clinical Feasibility Study Device GCC 1202: The Gamma Pod: A Clinical Feasibility Study (NCT02507960), a na na study. The primary outcome is Demonstration of the Feasibility and Safety of Delivering a Radiation Treatment Using the GammaPod (TM).

2. Clinical Question

This framing makes the study a feasibility assessment rather than a comparative effectiveness trial. The registry record also identifies acute toxicity, long-term toxicity, and adverse events from adhesive spray as secondary outcome topics. It does not report numerical findings for those outcomes beyond the adverse-event counts described in the safety information.

3. Trial Design

This was a completed, single-group clinical feasibility study of the Gamma Pod in breast cancer. The registry record lists University of Maryland, Baltimore as sponsor, gives enrollment as 17, and records the study status as completed. The study started in 2016-01 and its primary completion date is 2017-06-30. The phase is recorded as NA.

Participants were intended to undergo breast-conserving therapy. The planned radiation approach was an 8 Gy tumor-bed boost using the Gamma Pod, followed by conventional whole-breast radiation of 50Gy in 25 fractions or hypofractionated whole-breast radiation of 40Gy in 15 fractions. The record describes the tumor-bed CTV as the surgical cavity, defined by surgical clips and postsurgical changes, plus 5 mm. It describes the PTV as adding 5 mm to the CTV to account for geometric uncertainties.

The pilot arm description says participants would undergo conventional CT simulation in a supine position without the breast immobilization cup. The stated purposes included assessing whether the tumor-bed volume could be delineated accurately and whether it was too large for a Gamma Pod boost. The registry record also lists CT simulation as an intervention.

There was no randomized allocation, masking, or control group recorded. With a single group, the design can describe experience among participants treated or assessed in the study, but it cannot estimate a between-group treatment contrast. The record does not report the detailed recruitment process, participant flow, treatment received by each participant, or a statistical analysis plan. The primary feasibility outcome result is 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

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 Demonstration of the Feasibility and Safety of Delivering a Radiation Treatment Using the GammaPod (TM), measured over 1 year.

The primary endpoint is described as the demonstration of feasibility and safety of delivering radiation treatment using the Gamma Pod. Its unit is participants, and the outcome type is a count of participants. The registry description links feasibility to coverage of the target volume with appropriate dose homogeneity and conformity, as defined in the study.

Eligibility also depended on tumor-bed CTV size: the CTV had to be less than 25% of the whole-breast PTV, a criterion the record associates with partial-breast-alone trials. The record says a patient whose tumor bed could not fit this criterion would be unable to receive Gamma Pod treatment. These details establish a practical constraint on whether the planned target can be treated with the device.

In general, a participant count can be useful in a feasibility study because it describes how many participants meet a prespecified operational criterion. The count is most informative when the record also makes clear how success is defined, who was assessed, and how unevaluable cases are handled. Although the registry describes target coverage, homogeneity, conformity, and the size criterion, it does not report the number meeting the primary endpoint or a detailed rule combining these elements. The primary endpoint result is not reported in the registry record, so feasibility cannot be quantified from the posted results.

The endpoint is not a direct comparison of clinical benefit between radiation approaches. The registry record does not report a comparative endpoint or a control group. Nor does the endpoint description alone establish the duration or completeness of follow-up for each participant.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical interpretation begins by matching the method to the study design and outcome. This is a single-group feasibility study with a participant-count primary endpoint. There is no randomized comparison, and the registry record lists no analysis entries. Accordingly, interpretation should focus on what was observed in the study group and what remains unreported, rather than on a treatment contrast.

What does a participant count describe?

A count records how many participants meet a defined condition. For a feasibility endpoint, that condition might involve an operational requirement such as target coverage or treatment eligibility. A count is easy to understand, but it needs a clear definition and an assessment denominator. The registry record gives the enrollment as 17 and describes feasibility criteria involving target coverage, dose homogeneity, conformity, and CTV size. It does not report the primary endpoint count or explain in detail how the criteria were combined into a success classification.

Counts are often accompanied by a proportion and an interval describing uncertainty. A confidence interval is a range of values compatible with the observed data under a specified statistical model; it conveys precision rather than guaranteeing that a value is correct. No confidence interval for the primary endpoint or for the adverse-event counts is reported in the registry record. No such interval should be inferred from the counts alone in this explanatory text.

Why does the single-group design matter?

A single-group study has no concurrent control group. It can describe whether a procedure or device was used, the feasibility criteria assessed, and events recorded among participants. It cannot by itself estimate what would have happened to the same participants under a different approach. Differences between populations, care settings, follow-up, and event definitions can also make comparisons with other studies difficult. The registry record identifies no allocation to a comparison arm and no masking.

In a randomized comparative study, allocation can support a balanced comparison by distributing measured and unmeasured participant characteristics across groups in expectation. That logic does not apply to this single-group design. A low or high event count, if reported, would remain a descriptive finding in this group rather than an estimate of relative risk attributable to the Gamma Pod.

How should adverse-event counts be read?

The safety record distinguishes serious adverse events from other adverse events. For the Pilot Study group, it reports 17 participants at risk for serious events, with zero affected, and 17 at risk for other events, with 14 affected. These are participant counts, not event counts: the record describes the number of participants with an event. The distinction matters because one participant may experience more than one event, but the available figures do not state how many individual events occurred or whether multiple events affected the same participant.

In general, zero recorded serious events does not show that the underlying risk is exactly zero. The interpretation depends on the number assessed, the length and completeness of observation, and how events were defined and collected. Those details are not fully reported in the registry record. Likewise, the reported count for other adverse events does not identify the event types, severity distribution, timing, or relation to treatment.

What role would a confidence interval play?

In general, a confidence interval around a proportion or count-based estimate communicates how much uncertainty is compatible with the data and the statistical assumptions. It can be particularly useful in a small feasibility study, where a point estimate alone may give a misleading impression of precision. However, the registry record does not report intervals or a statistical model for the primary endpoint or safety summaries. The available information therefore supports reporting the counts as recorded, without adding a precision estimate.

What is over-dispersion, and does it apply?

In general, over-dispersion occurs when count variability is greater than a chosen probability model expects. It can matter when modeling counts of events, particularly if participants contribute multiple events or their event rates differ substantially. The registry’s safety summary is expressed as participants with an event rather than a total event count, and no count model or analysis is reported. There is therefore no basis in the record to assess over-dispersion or to select an over-dispersion adjustment.

How should planning illustrations be distinguished from trial results?

In general, a sample-size planning calculation asks how many participants a future study might need under stated assumptions. It is not an observed result and does not measure the power achieved by a completed study. The planning assumptions associated with this analysis describe a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and effects expressed as a stated fraction of an observed effect. Those assumptions are illustrative and do not describe the design of this single-group trial. The record does not report the trial’s own sample-size justification, and the assumptions do not supply a primary endpoint result.

For time-to-event outcomes, general sample-size methods may be framed around the number of events rather than the number of participants. That distinction does not establish that the present primary endpoint was analyzed as time-to-event; its recorded unit is participants and its parameter is a count of participants. The registry record does not report time-to-event analyses.

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("Pilot Study")
n      <- c(17)
events <- c(14)
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  Pilot Study  17  14  82.4  56.6  96.2  59.0  93.8  58.6  93.6

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists four outcome measures and describes several outcome topics: the primary feasibility and safety question, acute toxicity, long-term toxicity, and adverse events associated with adhesive spray. Listing multiple outcomes does not establish that formal hypothesis tests were conducted. The record has no analysis entries, and it does not report a multiplicity procedure, a hierarchy of tests, or a prespecified distinction between confirmatory and exploratory analyses. The handling of multiplicity is therefore not reported in the registry record.

Multiplicity matters when several statistical tests are interpreted together. In general, the more opportunities there are to declare a finding, the greater the chance of at least one apparently notable result arising by chance if each test is considered separately. Methods such as prespecified outcome hierarchies or adjusted thresholds can address this issue, but the registry record does not say whether any such approach was planned or used. No claim about statistical significance should be inferred from the outcome list.

Missing-data handling is also not reported in the registry record. The record gives enrollment as 17 and safety denominators of 17 participants at risk for both serious and other adverse events, but it does not describe completeness of follow-up, withdrawal, missing assessments, or how such cases were treated in endpoint summaries. Those denominators alone do not establish that every participant had complete outcome ascertainment through the stated timeframes.

The registry record does not define analysis populations, such as whether primary endpoint assessment included all enrolled participants or only those who received treatment. It also does not report exclusions, protocol deviations, or a method for handling participants who could not be treated because of target-volume criteria. These omissions limit assessment of the denominator and of potential selection effects.

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 non-serious adverse event terms

The safety summary identifies a Pilot Study group. It reports 17 participants at risk for serious adverse events and zero affected. For other adverse events, it reports 17 participants at risk and 14 affected. These figures are participant counts, not a count of all individual events. They should be read as the number of participants recorded as having at least one event in each category.

The registry record lists acute toxicity evaluation during and up to one month after the Gamma Pod tumor-bed boost, long-term toxicity evaluation at one year for subcutaneous fibrosis and fat necrosis, and adverse events from adhesive spray. It does not provide numerical results separately for these outcome descriptions, nor does it report event terms in the serious category. The counts therefore cannot be assigned to specific toxicity types or timepoints from the information recorded.

In general, a zero count is not evidence that an event is impossible. Its interpretation depends on the observation period, completeness of follow-up, event definitions, and whether events were actively assessed. Those details are not fully reported in the registry record. The group counts are descriptive and, with no comparator, do not establish how safety would differ under another treatment approach.

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

The record describes a feasibility study of a breast-specific radiosurgery device in the setting of breast-conserving therapy. It specifies a planned 8 Gy tumor-bed boost followed by one of two whole-breast radiation schedules, and it describes anatomical and dosimetric considerations relevant to whether the target could be treated. The study’s stated purpose was to demonstrate feasibility and safety.

The primary endpoint result is not reported in the registry record. Consequently, the posted information does not quantify how many participants met the feasibility criteria or establish how often target coverage, dose homogeneity, and conformity were judged adequate. The record also does not report a detailed success rule or the number of participants who received the planned Gamma Pod treatment. Enrollment of 17 participants is not itself evidence that the primary feasibility endpoint was met.

The safety information reports zero participants with serious adverse events among 17 at risk and 14 participants with other adverse events among 17 at risk. These are descriptive counts. They do not establish the cause of events, their specific types, their severity beyond the serious-versus-other distinction, or their timing. They also do not establish comparative safety, because the study has no control group.

In general, feasibility studies can help characterize whether procedures and assessments can be carried out and can identify practical issues for later research. They are not necessarily designed to establish comparative benefit or to give precise estimates of uncommon harms. The registry record does not report a sample-size justification for this trial, an analysis plan, or inferential results that would support a broader claim.

The study therefore contributes a description of the planned approach and recorded safety counts, but the available record leaves the main feasibility outcome unresolved. It does not establish that the Gamma Pod is better or worse than another treatment, nor does it determine the clinical consequences of using the device. Such conclusions would require results and comparative evidence not reported in the registry record.

14. Why This Trial Matters Statistically

This study raises statistical questions that are central to early clinical evaluation of a device. Feasibility is not captured by the name of the intervention or by enrollment alone; it depends on operational criteria that can be assessed consistently. The registry record identifies target coverage, dose homogeneity, conformity, and a tumor-bed CTV size criterion, making clear that technical suitability was part of the clinical question.

For a feasibility outcome to be interpretable, the record needs to report who was assessed, the decision rule, and the number meeting it. Those details allow readers to distinguish successful delivery from screening, planning, or eligibility. The primary endpoint count is not reported in the registry record, so the stated question cannot be answered from the posted outcome information. That gap is statistically important, not merely a matter of presentation.

The single-group design also shapes what the study can establish. It allows description of experience in the study group but does not create a valid comparison with another treatment. This distinction prevents an observed count from being interpreted as evidence of relative effectiveness or safety. The adverse-event counts are informative as descriptive observations, while the lack of a comparator and detailed event information constrains broader interpretation.

Finally, feasibility research and definitive comparative research answer different questions. A planning illustration based on an observed effect is not the same as the trial’s own design justification, and a projected sample size is not observed power. Keeping planning assumptions separate from trial results helps readers avoid treating hypothetical calculations as findings. The registry record does not report its own sample-size justification or statistical analysis plan, which limits assessment of how the study was designed to address its primary question.

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 most consequential limitation of the registry record is that it does not report the primary feasibility endpoint result. Although the endpoint description identifies target coverage, dose homogeneity, conformity, and a tumor-bed CTV size criterion, the number of participants meeting the endpoint is not available. The record also does not give a detailed rule for combining these considerations into a final feasibility classification.

The study is single-group and has no comparator. Its findings therefore cannot quantify a difference from another radiation approach or support a causal comparison. Allocation is recorded as NA and masking as none. The record does not explain whether all enrolled participants received the Gamma Pod treatment, how many were eligible after target assessment, or whether any participants were unable to proceed.

The safety summary is limited to participant counts in serious and other adverse-event categories. The record does not provide event terms for the serious category, specific types or severity for the other category, timing, attribution, or a breakdown by the acute, long-term, and adhesive-related outcome descriptions. It also does not report completeness of follow-up or missing assessments. The counts should therefore not be taken as a complete characterization of the safety experience.

The registry record lists four outcome measures but has no analysis entries. It does not report confidence intervals, hypothesis tests, adjusted analyses, a multiplicity approach, analysis populations, or missing-data methods. A statistical analysis plan and a sample-size justification for the trial are not reported in the registry record. The available information is accordingly insufficient to assess precision, prespecification, or the handling of incomplete data.

The pilot arm description gives information about supine CT simulation without the breast immobilization cup and its stated purposes, but it does not provide a full account of implementation or participant flow. These limitations restrict interpretation to the study’s recorded design features and the specific safety counts available.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: The Gamma Pod: A Clinical Feasibility Study Device GCC 1202: The Gamma Pod: A Clinical Feasibility Study — NCT02507960.
• Registry record last updated 2022-01-14; status last verified 2022-01.
• Results first posted 2022-01-14.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

The registry record describes a completed, single-group feasibility study of the Gamma Pod for breast-conserving therapy in breast cancer. It reports enrollment of 17 participants, University of Maryland, Baltimore as sponsor, and a primary completion date of 2017-06-30. The planned approach was an 8 Gy tumor-bed boost followed by conventional whole-breast radiation of 50Gy in 25 fractions or hypofractionated radiation of 40Gy in 15 fractions.

The primary endpoint concerned feasibility and safety, including target coverage, dose homogeneity, conformity, and a tumor-bed CTV size criterion. The primary result is not reported in the registry record. Safety counts show zero participants with serious adverse events among 17 at risk and 14 participants with other adverse events among 17 at risk. The record does not report analysis entries, a statistical analysis plan, or detailed outcome results for the listed toxicity measures. With no comparator group, the study provides descriptive information rather than a comparative treatment estimate.