Iodine I 131 in Treating Patients With Thyroid Cancer: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Iodine I 131 in Treating Patients With Thyroid Cancer (NCT00416949), a na na study. The primary outcome is Tumor Absorbed Dose.

2. Clinical Question

The registry summary gives a broader purpose: to study side effects, best dose, and how well iodine I 131 works in treating patients with thyroid cancer. The listed primary outcome, however, is a dose measurement calculated from imaging, not a direct measure of tumor response or clinical benefit. The intervention entry names patient-specific dosimetry, rather than describing a comparator treatment. The record does not report a comparison that could estimate the difference between dosimetry strategies or between treatment and control.

The registry reports that tumor data from 3 patients could be analyzed because only tumors that could be reliably imaged were suitable for analysis. It does not report the calculated dose values. Thus, the stated question can be identified from the outcome definition, but the posted record does not give the result needed to describe the observed mean dose or its variability.

3. Trial Design

This is a single-group study with no masking. Allocation is recorded as NA, and the registry explicitly indicates that the study is not a randomized comparison. There is no like-for-like control arm described. The phase is listed as NA. Enrollment is recorded as 9.

The named intervention is patient-specific dosimetry, described as applying a calculation method to imaging data to estimate tumor absorbed doses using the 3D-RD method. The study title and summary concern iodine I 131 in thyroid cancer, but the intervention entry itself identifies dosimetry. The registry record does not provide enough detail to characterize additional treatment procedures or to establish which participants received what treatment.

The study start is recorded as 2006-04, and primary completion as 2009-10. Its status is listed as terminated; a reason for termination is not reported in the registry record. The primary outcome timeframe is up to 4 years. The record lists one outcome measure and zero analyses. It identifies the primary outcome as tumor absorbed dose in Gy, summarized by a mean and standard deviation.

Enrollment and the primary outcome's analysis population are not interchangeable. The registry says tumor data from 3 patients could be analyzed, based on the number of tumors that could be reliably imaged for analysis. This means the outcome information pertains to an imaging-selected subset, rather than all enrolled participants. Further details about the selection process, missing imaging, follow-up, or participant flow are not reported in the registry record.

The sponsor is Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins. The record does not describe a randomized assignment, masking, or a comparison group that would support treatment-effect contrasts. The design is therefore best read as a single-group dosimetry study, with a limited set of analyzable tumor data, rather than as a controlled test of the clinical effectiveness of iodine I 131.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Was only able to analyze tumor data from 3 patients based on number of tumors that could be reliably imaged for analysis.

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 Tumor Absorbed Dose, measured over up to 4 years.

The primary endpoint is tumor absorbed dose, measured in Gy and calculated using patient-specific dosimetry. Absorbed dose describes radiation energy deposited in a target per unit mass. In general, estimating dose at the tumor level can help characterize how much radiation a tumor is calculated to receive, rather than relying only on a treatment amount that may not reflect differences between patients or tumors.

The registry specifies that the outcome is summarized as a mean and that its dispersion is described using standard deviation. A mean gives a central summary of the measured or calculated values. Standard deviation describes how spread out those values are around the mean; it is not the same as uncertainty in the mean. These summaries are useful for describing both a typical value and variation in the observed dose data.

The registry says the dose calculation used patient-specific imaging and that tumor data from 3 patients could be analyzed because only reliably imaged tumors were suitable. It does not report the actual mean dose, standard deviation, number of tumors analyzed, or individual dose values. The timeframe is listed as up to 4 years, but measurement timing details are not reported in the registry record.

This endpoint is a dosimetry measure, not itself a measure of tumor shrinkage, disease control, symptoms, or survival. Its value for interpreting clinical outcomes would depend on information linking dose estimates to such outcomes, which is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: tumor absorbed dose is expressed in Gy and summarized as a mean with standard deviation. In general, a continuous outcome can take a range of numerical values. A mean compresses a set of observations into a central summary, while the standard deviation describes dispersion among those observations. Together, they can convey both the average dose and how much dose values vary. Neither statistic is available as a numerical result in the registry record.

The standard deviation should not be read as a confidence interval. In general, a confidence interval describes uncertainty around an estimated quantity, while standard deviation describes the spread of individual observations. A confidence interval for the mean would require additional information and a specified method. No such interval or method is reported in the registry record. The record also does not give a standard error or a distributional description of the dose values.

The primary outcome depends on image-based tumor measurement. The arm description says the 3D-RD method was applied to imaging data to calculate tumor absorbed doses. The registry notes that tumor data from 3 patients could be analyzed because only tumors that could be reliably imaged were suitable for analysis. This is not simply a matter of a smaller count: image reliability determines which tumors contribute data. In general, when inclusion in an analysis depends on measurement availability or quality, the analyzed observations may not represent all observations initially considered. Whether that occurred in this study cannot be determined from the registry record.

In general, measurement error can affect both the estimated mean and the apparent variability of a continuous endpoint. Patient-specific dosimetry may account for individual imaging information, but the registry description alone does not establish the accuracy or validation of the calculation method. Details such as imaging procedures, dose-calculation specifications, quality checks, and handling of uncertain measurements are not reported in the registry record. It would therefore be inappropriate to infer the degree of measurement error or to compare the method with another approach.

The record lists a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It says the effect to detect is a stated fraction of the observed effect. For time-to-event illustrations, the calculation is expressed as a total number of events; other illustrations are expressed as participants per arm. These are general planning assumptions, not evidence that the study itself used a two-arm design. The actual study is listed as single-group, with allocation recorded as NA.

A planning calculation asks what sample size might be needed under specified assumptions. It is not an observed result and does not show the probability that this completed or terminated study detected an effect. In particular, planning based on an observed effect is conditional on that effect estimate and the assumptions used for the illustration. The registry does not report a sample-size justification for the trial's own design, and the posted record contains no numerical primary outcome result from which to assess an observed effect.

The record lists zero analyses. It therefore does not describe an inferential procedure for the primary endpoint, such as a test, a confidence-interval method, an adjustment for covariates, or a model for repeated observations. Those methods are not reported in the registry record. A stated outcome summary of mean and standard deviation does not by itself tell readers how uncertainty was quantified or whether any hypothesis was tested.

Over-dispersion is a concern in some count-data models when variation exceeds what a simple model assumes. In general, that issue is not the central one for the stated continuous mean endpoint; the more directly relevant questions are how dose values were measured, how image reliability determined inclusion, and how uncertainty around the mean would be estimated. No count model or over-dispersion analysis is reported in the registry record. The general distinction helps prevent methods for one outcome type from being assumed for another.

The main statistical reading is consequently limited to the outcome definition, measurement description, and analysis-population note. No numerical estimate, inferential result, or uncertainty interval is available in the registry record. Any hypothetical sample-size exercise should be treated as a planning illustration under its stated assumptions, not as evidence about the precision or power of this study.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Patient-specific 3D-RD Dosimetry")
n   <- c(3)
m   <- c(6.6)
sp  <- c(4.54)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Patient-specific 3D-RD Dosimetry  3  6.600  4.540  -4.678  17.878

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure and zero analyses. It does not describe a multiplicity plan, a hierarchy of outcomes, or adjustments for testing more than one hypothesis. Because no analyses are listed, there is no posted set of statistical tests from which to assess multiplicity in practice. The broad aims in the summary mention side effects, best dose, and how well iodine I 131 works, but the listed primary outcome is tumor absorbed dose. Whether additional outcomes were planned or assessed is not reported in the registry record.

The record identifies tumor data from 3 patients as analyzable because only tumors that could be reliably imaged were suitable. It does not describe missing-data methods, imputation, sensitivity analyses, or how tumors without reliable images were handled beyond their exclusion from the analysis. In general, missingness can affect interpretation when the availability of a measurement is related to the value being measured or to participant characteristics. The registry does not provide enough information to determine whether such a relationship existed.

The number enrolled is recorded as 9, but the primary outcome description refers to analyzable tumor data from 3 patients. The record does not provide a participant flow account or a complete explanation of how enrollment relates to the imaging-based analysis population. It also does not report an intention-to-treat analysis or another prespecified analysis population. These omissions limit assessment of selection and missing-data effects.

The registry does not report interim analyses, a prespecified statistical analysis plan, or a sample-size justification for the actual study. Such details should not be inferred from the planning assumptions listed for illustrative calculations.

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.

The adverse-event record lists the patient-specific 3D-RD dosimetry group with 3 participants at risk for serious adverse events and 0 affected. It also lists 3 at risk for other adverse events and 0 affected, with 0 deaths. No serious adverse-event terms are listed.

These figures describe the recorded safety counts in the listed group; they do not establish that no adverse events occurred outside the recorded categories or observation period. The registry does not provide event-level details, definitions, observation timing, or an explanation of how safety information was collected. It also does not report a comparison group, so these counts cannot support a comparative safety estimate.

The safety figures should be read alongside the outcome-population limitation: the primary outcome description says tumor data from 3 patients could be analyzed, while the adverse-event record separately lists the group counts at risk. The record does not explain whether those populations are identical. Zero recorded events in the listed counts is not proof of zero risk, and it does not establish the safety of iodine I 131 or of dosimetry more generally.

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

The registry record describes a single-group study using patient-specific dosimetry to calculate tumor absorbed dose from imaging data. It identifies the primary endpoint, its unit, its summary measures, and the timeframe. It also reports that only tumors that could be reliably imaged contributed analyzable tumor data, with data from 3 patients identified for analysis.

What the result does not provide is the numerical mean dose or its standard deviation. It also does not provide an inferential analysis, confidence interval, or clinical outcome analysis connecting dose estimates to tumor response, disease control, or survival. As a result, the posted record cannot establish the level or precision of the observed dose distribution, nor can it support a conclusion about how well iodine I 131 works.

The design limits causal interpretation. There is no comparator arm, and the study is not randomized. The primary outcome is a calculated dose rather than a direct measure of treatment benefit. The registry's broader purpose statement should not be mistaken for a posted result on efficacy or dose selection. No best dose can be identified from the information recorded.

The adverse-event counts record 0 serious events, 0 other adverse events, and 0 deaths in the listed group, with 3 at risk in each event category. These descriptive counts do not prove absence of harm, establish a comparative safety profile, or resolve whether the safety population matches the imaging analysis population.

The most supportable conclusion is methodological and descriptive: the record documents an imaging-based, patient-specific dose calculation approach and a restricted analyzable set tied to reliable imaging. Numerical dose results and the analyses needed to assess precision or clinical implications are not reported in the registry record. The study's terminated status is recorded, but its reason and implications for completion are not reported.

14. Why This Trial Matters Statistically

This study illustrates how the definition of an endpoint and the availability of measurements shape what can be learned from a clinical record. The primary outcome is tumor absorbed dose, a continuous quantity calculated using patient-specific imaging. Such a measure can describe radiation dose at the tumor level, but it does not directly answer whether a treatment improves a clinical outcome.

The imaging restriction is particularly important. The registry says only tumors that could be reliably imaged were suitable for analysis and identifies tumor data from 3 patients. This makes the analysis population a central part of interpretation, rather than a technical detail. Readers need to know not only what was measured, but also which measurements were considered reliable enough to include and how that selection may affect representativeness.

The record also demonstrates the limits of a single-group design. Without a comparator, there is no direct estimate of how outcomes would differ under another approach. A calculated dose can be described, but comparisons and causal claims require information this record does not provide. Similarly, event counts without a comparison group and fuller safety details are descriptive rather than comparative.

Finally, a stated mean and standard deviation do not replace the result itself. Without numerical estimates or an inferential analysis, readers cannot evaluate the dose level, variation, or precision. The distinction between an illustrative sample-size calculation and the design actually used is also essential: hypothetical planning assumptions do not become evidence about study power or efficacy.

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 primary outcome is dependent on tumor imaging, and the registry reports that only tumors that could be reliably imaged were suitable for analysis. Tumor data from 3 patients are identified as analyzable, while enrollment is recorded as 9. The record does not describe the characteristics of tumors or participants with unavailable or unreliable imaging, so the potential effect of this selection cannot be assessed.

No numerical result for tumor absorbed dose is reported. Although the endpoint is defined as a mean with standard deviation, the registry does not give either value, individual measurements, a confidence interval, or an analysis method. The listed timeframe is up to 4 years, but the timing of dose measurements and completeness of follow-up are not reported in the registry record.

The design is single-group, allocation is NA, and no comparator is described. The study is not a randomized comparison, so the record does not support a treatment contrast. The intervention entry describes patient-specific dosimetry; further details about treatment delivery or the use of calculated dose in clinical decisions are not reported in the registry record.

The study is listed as terminated, but the reason is not reported. The registry also lists zero analyses, and it does not provide a statistical analysis plan, sample-size justification, interim analysis information, multiplicity approach, or missing-data method. These omissions constrain assessment of how the study was conducted and how robust any intended inference would have been.

Safety reporting is limited to the posted counts and absence of listed serious-event terms. Event definitions, follow-up duration, collection procedures, and the relation between the safety group and the imaging analysis population are not reported. These limitations prevent broader conclusions about safety or clinical effectiveness.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Iodine I 131 in Treating Patients With Thyroid Cancer — NCT00416949.
• Registry record last updated 2018-07-18; status last verified 2018-06.
• Results first posted 2018-07-18.
• 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

NCT00416949 is a terminated, single-group study titled Iodine I 131 in Treating Patients With Thyroid Cancer. Its listed intervention is patient-specific dosimetry using the 3D-RD method, applied to imaging data to calculate tumor absorbed dose. Enrollment is recorded as 9, and the registry lists the phase as NA, no masking, and allocation as NA.

The primary outcome is tumor absorbed dose in Gy, summarized as a mean and standard deviation over up to 4 years. The record says tumor data from 3 patients could be analyzed because only reliably imaged tumors were suitable. It lists one outcome measure and zero analyses, but reports no numerical dose result.

The adverse-event record lists 0 serious events, 0 other events, and 0 deaths, with 3 at risk in each event category. The study start is recorded as 2006-04 and primary completion as 2009-10. The reason for termination and further analysis details are not reported in the registry record.