Here is the design of a clinical trial:

Official Title: Active Surveillance or Surgery for Primary Management of Very Low Risk Papillary Thyroid Cancer: How Often Are the Long-term Disease Management Goals Achieved?

Included conditions:
- Papillary Thyroid Cancer
- Papillary Thyroid Carcinoma
- Papillary Microcarcinoma of the Thyroid

Study Armgroups:
- {'label': 'Active Surveillance', 'description': 'Patients under active surveillance choose to not have immediate thyroid surgery. Patients are closely monitored with respect to clinical status, ultrasound imaging, biochemical indices (thyroid function, thyroglobulin, and thyroglobulin antibodies) and any thyroid cancer-related treatments (if received). Active surveillance is conducted at a participating study site. Criteria defining disease progression are established, and if such criteria are met, thyroid surgery is recommended to the patient. However, patients are free to choose to have thyroid surgery at any time, in the absence of disease progression. Thyroid cancer clinical and treatment outcomes are tracked by the study team.'}
- {'label': 'Immediate Thyroid Surgery (total or partial thyroidectomy)', 'description': "Patients who choose surgery, undergo thyroidectomy, as per current standards of care, by a surgeon of their choice in an institution of their choice. The treating surgeon, in discussion with the patient, will choose the extent of thyroid surgery that may be appropriate for the individual case. Post-surgical follow-up is per the discretion of the treating surgeon, endocrinologist, or other healthcare providers involved in the patient's thyroid cancer care. Thyroid cancer clinical and treatment outcomes are tracked by the study team."}

Interventions:

Primary Outcomes:
- {'measure': "Number of Participants in the Active Surveillance Group who Experience 'Failure' of Active Surveillance Disease Management", 'description': "'Failure' of Active Surveillance Disease Management is defined as: surgery for the indication of thyroid cancer that has progressed during study monitoring. Thyroid cancer disease progression under active surveillance includes: a) thyroid cancer enlargement \\> 3mm in largest dimension, b) thyroid cancer growth in a location that is concerning (e.g. extension outside of the thyroid, concerning proximity to critical structures such as the trachea or recurrent laryngeal nerve), or c) development of metastatic disease (in lymph nodes or distant organs). The specific type of disease progression will be reported.", 'timeFrame': 'Through study completion, an estimated average of 3 years'}
- {'measure': "Number of Participants in the Surgical Group who Experience 'Failure' of Surgical Disease Management", 'description': "For patients who choose immediate surgery for management of thyroid cancer, the intent of surgery is curative. Thus, 'failure' of surgical disease management is defined by receiving additional treatment for structural thyroid cancer detected at follow-up (i.e. treatment of thyroid cancer detected on imaging or biopsy during follow-up). Additional thyroid cancer treatment may include additional surgery, radioactive iodine, ethanol ablation of lymph nodes, or external beam radiation treatment. The specific treatment used for recurrent or persistent thyroid cancer and the indication for the treatment will be reported.", 'timeFrame': 'Through study completion, an estimated average of 3 years'}

Please estimate the sample size based on the assumption: 
The sample size is calculated to achieve a 95% confidence interval half-width of 2% around the estimate of 3% disease management 'failure' in the AS arm, with an 80% chance that the CI half-width will be narrower than 2.1%.
Sample Size Calculation
        Statistical assumptions justifying our proposed total sample size of 450 patients (in total, including consenting patients from the original Toronto study as well as patients from all participating sites recruited in the multi-center study) are as follows, as they relate to the primary outcome analysis: i) Based on our current preliminary data from Toronto (September, 2020), the ratio of those choosing AS to those choosing surgery will be 3:1. ii) Based on published data from a prior published retrospective study of Toronto patients under the care of a primary investigator (AMS), it is expected that within an approximately 5-year time frame, approximately 3.4% of low risk papillary thyroid cancer patients in the surgical arm will receive treatment for recurrent disease (17). For purpose of sample size calculations this number is rounded down to 3%, in the time frame of about 2 to 3 years. Based on published data on active surveillance of VL-PTC, which is largely based on papillary microcarcinomas (7), we estimate that after about 2 - 3 years of follow-up, the cumulative incidence of disease progression requiring surgery in the AS arm will be approximately 3% (including both tumor growth and incident nodal metastatic disease). The sample size is guided by estimation of disease management âfailureâ (absence of success) in the AS arm, as outcomes with surgery are better established. To estimate the risk of âfailureâ of disease management in the AS group with an expected 95% confidence interval half-width of 2% (e.g., a confidence interval of 2% around the estimate of 3%), the required sample size is 328; there is an 80% chance the CI half-width will be narrower than 2.1%. Under the 3:1 ratio assumption above, approximately 110 surgical patients need to be recruited to obtain 328 AS patients. In order to accommodate some attrition in both groups, we plan to recruit a total of 450 patients (including patients consenting to long-term follow-up from the original Toronto study) and expect approximately 330 in AS group and 120 in the surgical group). Recruitment of surgical arm patients will enable controlled comparisons for the secondary outcomes. The sample size will be re-evaluated on a yearly basis, and the total sample size may be adjusted accordingly to maintain the desired precision in the AS arm.