Here is the design of a clinical trial:

Official Title: Randomized Trial Assessing Induction of Double Strand Breaks With Androgen Receptor Partial Agonist in Patients on Androgen Suppression

Included conditions:
- Prostate Cancer

Study Armgroups:
- {'label': 'flutamide', 'type': 'EXPERIMENTAL', 'description': '50mg flutamide prior to brachytherapy and prostatic biopsy', 'interventionNames': ['Drug: Flutamide']}
- {'label': 'placebo', 'type': 'PLACEBO_COMPARATOR', 'description': 'placebo prior to brachytherapy and prostatic biopsy', 'interventionNames': ['Other: Placebo']}

Interventions:
- {'type': 'DRUG', 'name': 'Flutamide', 'description': '50mg flutamide prior to brachytherapy and prostatic biopsy', 'armGroupLabels': ['flutamide']}
- {'type': 'OTHER', 'name': 'Placebo', 'description': 'placebo prior to brachytherapy and prostatic biopsy', 'armGroupLabels': ['placebo']}

Primary Outcomes:
- {'measure': 'DNA double strand break formations', 'description': 'To confirm DNA double strand breaks occur in prostate cancer tissue following pulse-dose flutamide administration in patients who are androgen suppressed, as compared to control patients receiving placebo. Extent of Gamma H2Ax as a measure of DNA double strand break formation.', 'timeFrame': 'Post Flutimide exposure up to 12 hours'}

Please estimate the sample size based on the assumption: 
The study uses a Bayesian monitoring rule with a significance level of 50% for feasibility. The confidence intervals for the treatment group range from 0.35 to 0.42, and for the control group, it is less than 0.5. The dropout and non-evaluable rate is estimated at 20%.
Sample size justification and accrual
        This trial will be utilized to design a larger study to establish measures for such parameters with a reasonable level of precision. We will enroll 30 patients in the trial, with a goal of at least 24 evaluable patients accrued.
        In the run-in phase, a total of 6 evaluable patients will be accrued to receive Flutamide administration. We will use a Bayesian monitoring rule to determine if the study is feasible. Specifically, we would consider it âinfeasibleâ if the probability of not observing greater than or equal to 5% of prostate cancer cells having Î³H2Ax foci is more than 50%. Based on the Bayesian monitoring rule in Section 6.3, if there is less than or equal to 1 out of 6 cases with detectable DNA double-strand breaks (i.e., greater than or equal to 5% of prostate cancer cells having Î³H2Ax foci on patient level), the study will be considered as infeasible and will not proceed into the randomization part.
        If the study proceeds into the randomization part, a total of 18 evaluable patients will be randomized in a 2:1 ratio to either receive flutamide (12 patients) or not (6 patients). A simple randomization method will be utilized. A total of 18 patients treated with flutamide (6 from run-in and 12 from randomization) will produce a two-sided 90% confidence interval with a width ranging from 0.35 to 0.42 (if the true proportion of prostate cancer cells having Î³H2Ax foci is 30%-80%). A total of 6 patients in control will produce a two-sided 90% confidence interval with a width approximately less than 0.5 (if the true proportion of prostate cancer cells having Î³H2Ax foci is less than 10%).
        All eligible patients will be offered enrollment in the study, and we estimate a 20% dropout and non-evaluable rate. Patients who drop out prior to the biopsy/brachytherapy procedure will be replaced; patients who drop out after the biopsy/brachytherapy will not be replaced. In order to ensure at least 24 evaluable patients are available, we plan to enroll ~30 patients in this trial. Given the minimal addition to standard therapy and effort requirement from patients, we expect to accrue at least 2â3 patients/month, and the full accrual will be completed in 2 years.
        The feasibility of detecting DNA double-strand breaks will be based on the proportion of patients in whom Î³H2Ax foci are observed in â¥5% of prostate cancer cells. Conversely, the trial will be considered âinfeasibleâ if the probability of failure to observe DNA double-strand breaks is more than 50% and with more than 70% posterior probability. We assume there will only be a smaller proportion of cases in which DNA double-strand breaks cannot be observed, e.g., on average only 10% of patients will not have detectable DNA double-strand breaks and there will be about 16% chance that the risk will be 20% or more. This corresponds to a Beta (0.1, 0.9) prior distribution. Table 1 summarizes the continuous termination rule for the 18 evaluable patients treated with flutamide. The feasibility termination rule calls for the conclusion of the study without proceeding into the randomization part if there is less than or equal to 1 patient with detectable DNA double-strand breaks within the first 6 patients (in the run-in phase). If the trial enters the randomization phase, the feasibility-stopping rule calls for accrual suspension if the number of patients with detectable DNA double-strand breaks is too low.Table 1Stopping rule for feasibility# patients without detectable DNA double-strand breaks567891011Out of the total # evaluable patients6â78â91112â1314â1516â1718
        Table 2 summarizes the operating characteristics based on 5000 simulations with 18 evaluable patients in terms of how frequently the study would stop based on the stopping rule under different hypothetical feasibility rates, as well as the average sample sizes.Table 2Operating characteristics of the stopping rule for feasibilityUnderlying proportion without detectable DNA double-strand breaks0.40.50.60.70.8% of the time study stops19.3%44%74.8%92.4%99.4%Expected sample size16.314.111.18.76.9