Here is the design of a clinical trial:

Official Title: Direct to Implant Extracellular Matrix Hammock Based pre-or Retropectoral Breast Reconstruction

Included conditions:
- Breast Reconstruction

Study Armgroups:
- {'label': 'Retropectoral immediate breast reconstruction', 'type': 'ACTIVE_COMPARATOR', 'description': 'Participants are randomized to immediate breast reconstruction with the implant placed retropectoral.', 'interventionNames': ['Procedure: Retropectoral immediate breast reconstruction']}
- {'label': 'Prepectoral immediate breast reconstruction', 'type': 'ACTIVE_COMPARATOR', 'description': 'Participants are randomized to direct to immediate breast reconstruction with the implant placed prepectoral using acellular dermal matrix for support.', 'interventionNames': ['Procedure: Prepectoral immediate breast reconstruction']}

Interventions:
- {'type': 'PROCEDURE', 'name': 'Retropectoral immediate breast reconstruction', 'description': 'Immediate reconstruction with the implant placed in a standard fashion, i.e. retropectoral in combination with an acellular dermal matrix.', 'armGroupLabels': ['Retropectoral immediate breast reconstruction']}
- {'type': 'PROCEDURE', 'name': 'Prepectoral immediate breast reconstruction', 'description': 'Immediate breast reconstruction with the implant placed prepectoral supported by acellular dermal matrix alone.', 'armGroupLabels': ['Prepectoral immediate breast reconstruction']}

Primary Outcomes:
- {'measure': 'Breast animation deformity', 'description': 'Breast animation deformity (BAD) is one of the more unpleasant cosmetic results that can be seen after breast reconstruction with a retropectoral placed implant. The degree of breast distortion will be evaluated by two experienced plastic surgeons and classified according to the published classification by Spear S. Because the degree of breast distortion will be the primary outcome measure of this randomised trial, the sample size will be based on assumptions regarding the grade of distortion between groups. For this purpose, the distortion will be divided into two groups: 1) Severe distortion containing degree 3 and 4 and 2) Moderate distortion containing degree 1 and 2. In bilateral cases the most severe side will be the one used for comparison', 'timeFrame': '12 months'}

Please estimate the sample size based on the assumption: 
Significance level of 0.05 (one-sided), power of 0.95, and an interim analysis with 60% of the patients included using an O'Brien-Fleming type α-spending function with a significance level of 0.0114 at interim.
Sample size
        A non-parametric calculation of the sample size was made based on our assumptions and experience regarding the degree of BAD in the two groups. We used Fisherâs exact test for small sample sizes. Based on our experience we expected that approximately 60% of the patients who are reconstructed using subpectoral implant placement would suffer from BAD as opposed to 20% of the women who are reconstructed using prepectoral implant placement. By using these assumptions in combination with a significance level of 0.05 (one-sided) and a power of 0.95, the total sample size was calculated to 70 patients, 35 women in each group.
        However, a retrospective cohort study in women over 18âyears of age who had a unilateral or bilateral direct-to-implant breast reconstruction between November 2011 and December 2017 suggested the above sample size assumptions to be too conservative [15]. Therefore, we will conduct an interim analysis with 60% of the patients included (i.e. 0.6âÃâ70â=â42). The primary hypothesis will be tested conservatively with nâ=â42 patients applying an OâBrien-Fleming type Î±-spending function (i.e. Î±1* in [18]), resulting in a significance level of 0.0114 at interim and securing an experiment-wise type 1 error of maximal 0.05.
        The sample size is calculated using STATA, version 14.0 (StataCorp, College Station, TX, USA) using a two-sample proportion test.