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Sample size considerations for single-arm clinical trials with time-to-event endpoint using the gamma distribution
Junqiang Dai1, Jianghua He1, Milind A Phadnis1
1Department of Biostatistics and Data Science, University of Kansas Medical Center, Kansas City, KS, USA.
Contemporary Clinical Trials Communications
|September 4, 2024
Summary
This study introduces gamma distribution for calculating sample sizes in single-arm clinical trials with time-to-event endpoints. This offers a more flexible alternative to existing methods, improving accuracy when disease patterns deviate from standard assumptions.
Area of Science:
- Biostatistics
- Clinical Trial Design
- Survival Analysis
Background:
- Single-arm clinical trials frequently utilize time-to-event (TTE) endpoints.
- Current statistical software has limited options for sample size calculations in these trials.
- Commonly used parametric models assume exponential or Weibull distributions for survival times.
Purpose of the Study:
- To propose gamma distribution as a flexible parametric option for sample size calculations in single-arm trials with TTE endpoints.
- To develop a method for estimating the gamma shape parameter from existing literature.
- To assess the accuracy of this estimation and the impact of distribution misspecification.
Main Methods:
- A sample size calculation approach using gamma distribution with a known shape parameter was outlined.
- Methods for extracting gamma shape estimates from published data (median, IQR) were detailed.
- Simulations were conducted to evaluate the accuracy of extracted parameters and the effects of misspecification.
Main Results:
- Reasonably accurate gamma shape estimates can be obtained from studies with small sample sizes (<60) and low censoring (<20%).
- Using these estimates enables the design of new single-arm studies.
- Misspecification of the true survival time distribution can lead to under- or overestimation of sample size.
Conclusions:
- Gamma distribution provides a valuable alternative to exponential and Weibull distributions for single-arm TTE trial design.
- Simulation-based assessment confirms the reliability of gamma shape estimation.
- Caution is advised to prevent misspecification of the underlying survival time distribution.
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