Here is the design of a clinical trial:

Official Title: A Single-centre, Double-blinded, Randomised, Placebo-controlled, Phase II Study to Investigate the Safety and Efficacy of Mesenchymal Stem Cell for Radiation-induced Hyposalivation and Xerostomia in Previous Head and Neck Cancer Patients (MESRIX-III)

Included conditions:
- Xerostomia Following Radiotherapy

Study Armgroups:
- {'label': 'Stem cell group', 'type': 'EXPERIMENTAL', 'description': '60 patients will be randomized to receive adipose-derived allogeneic stem cells', 'interventionNames': ['Biological: Stem cells']}
- {'label': 'Placebo group', 'type': 'PLACEBO_COMPARATOR', 'description': '60 patients will receive placebo consisting of CryoStor10 (BiolifeSolutions), the freeze media for ASCs containing 10% Dimethyl sulfoxide (DMSO).', 'interventionNames': ['Biological: Placebo']}

Interventions:
- {'type': 'BIOLOGICAL', 'name': 'Stem cells', 'description': 'Each participant will be double-blindly randomized to receive either adipose-derived allogeneic stem cells or placebo consisting of CryoStor10 (BiolifeSolutions), the freeze media for ASCs containing 10% Dimethyl sulfoxide (DMSO).', 'armGroupLabels': ['Stem cell group']}
- {'type': 'BIOLOGICAL', 'name': 'Placebo', 'description': 'Each participant will be double-blindly randomized to receive either adipose-derived allogeneic stem cells or placebo consisting of CryoStor10 (BiolifeSolutions), the freeze media for ASCs containing 10% Dimethyl sulfoxide (DMSO).', 'armGroupLabels': ['Placebo group']}

Primary Outcomes:
- {'measure': 'Salivary gland function', 'description': 'Change in salivary gland function measured by a 4 months change in unstimulated whole saliva flow rate in the group receiving ASCs compared with the group of participants receiving placebo (control group receiving injections of CryoStor10 (BiolifeSolutions), the freeze media for ASCs).', 'timeFrame': '4 month'}

Please estimate the sample size based on the assumption: 
Power of 0.8, significance level (alpha) of 0.05, and a dropout rate of about 20%
Sample size
        From our previous study MESRIX-I we assess to increase saliva production for whole unstimulated whole saliva flow rate (in ml/min) by about 33% or in absolute numbers from 0.125 to 0.155 after 4Â months. The power calculation is based on a power of 0.8 and an alpha of 0.05. This means that the total number of patients included would have to be 100 (50 in each group). We expect a dropout rate of about 20% and therefore aim to include 120 participants in total.