Here is the design of a clinical trial:

Official Title: Internet-based WOrk-related Cognitive Rehabilitation for Cancer Survivors: a Randomized Controlled Trial

Included conditions:
- Cognitive Problems

Study Armgroups:
- {'label': 'Basic Cognitive Rehabilitation', 'type': 'EXPERIMENTAL', 'description': 'The basic arm will consist of a brief cognitive training programme without individual guidance throughout the intervention, involving three to five sessions (each approximately 60 minutes in duration), which have to be completed in a period of 12 weeks.', 'interventionNames': ['Behavioral: online cognitive rehabilitation']}
- {'label': 'Extensive Cognitive Rehabilitation', 'type': 'EXPERIMENTAL', 'description': "The extensive arm will consist of a comprehensive training program, involving five to eight sessions (each approximately 60 minutes in duration), which have to be completed in a period of 12 weeks. After the first session, each further session in the extensive group involves tailored therapy guidance . Cognitive strategy modules will be assigned by the therapist depending on the participants' cognitive profile and personal treatment goals.", 'interventionNames': ['Behavioral: online cognitive rehabilitation']}
- {'label': 'Waitlist control group', 'type': 'NO_INTERVENTION', 'description': 'Participants in the waiting list control group will be offered the opportunity to follow the basic cognitive rehabilitation program after completion of the 26-week follow-up measurement.'}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'online cognitive rehabilitation', 'description': 'The cognitive rehabilitation program will be based on the protocol of a frequently used meta-cognitive strategy approach applied in many rehabilitation centers in the Netherlands. The program consists of several modules that can be used in a flexible way, depending on the specific individual problems and goals. Therapists have undergone additional training in issues related to cancer-related cognitive impairment and problems occupationally active cancer survivors might experience at work. In both intervention arms, participants will receive access to a secured personal webpage, where all content relevant to the treatment sessions can be obtained.', 'armGroupLabels': ['Basic Cognitive Rehabilitation', 'Extensive Cognitive Rehabilitation']}

Primary Outcomes:
- {'measure': 'Change from baseline Goal Attainment Scaling (GAS) at 3 and 6 months follow-up.', 'description': "Individually defined work-related treatment goals will be measured using the 6-point Goal Attainment Scale (GAS) on personal outcome (-3, achievement of the goal after training is worse; -2, achievement of the goal is the same; 1, partial achievement of the goal; 0, achievement of the goal; 1, exceeding the goal, and 2, greatly exceeding the goal). Patients will formulate three treatment goals at baseline, in collaboration with their cognitive therapist. Attainment of the goals is measured in a standardized way, i.e., an overall GAS T-score will be computed for each participant on basis of aggregated GAS scores involving attainment of multiple personal treatment goals, according a summary scoring algorithm that calculates the extent to which patients' goals are met.", 'timeFrame': 'T0 (baseline), T1 (12 weeks), T2 (26 weeks)'}

Please estimate the sample size based on the assumption: 
Alpha = 0.05, 80% power, and an attrition rate of approximately 20%.
Sample size calculation
        This longitudinal study design will allow for testing of the main effect of the intervention over time, with the GAS score as the primary outcome measure. With a sample size of 65, and an alphaâ=â0.05, the study will allow for an attrition rate of approximately 20% and have 80% power to detect an effect size of fÂ =â0.2 (equivalent to Cohens dÂ =â0.4) for the main effect of the intervention between both the basic and extended cognitive rehabilitation treatment group versus the waitlist control group (first hypothesis). To perform subgroup analysis, used to test our second hypothesis, sample size should be inflated fourfold [50]. Therefore, we strive for a sample size of 261, with 87 patients in each group.