Draw a Circle on Map

Hi everyone.
I need to draw a circle with the desired radius on the map, which is filled inside the circle with a transparent color and visible inside it. I did this according to the telerik tips, but the circle drawn on the map does not change its radius.
Can anyone help in this matter?
This is also my code:

**************draw circle Class **************

public class DrawCricleOnMap : MapPoint
    {
        private int radiusInMeters;

        public DrawCricleOnMap(PointG location) : base(location)
        { }

        public DrawCricleOnMap(PointG location, Size size)
            : base(location, size)
        { }

        public int RadiusInMeters
        {
            get
            {
                return this.radiusInMeters;
            }
            set
            {
                this.radiusInMeters = value;
            }
        }

        public override void ViewportChanged(IMapViewport viewport, ViewportChangeAction action)
        {
            double onePixelInMeters = MapTileSystemHelper.GroundResolution(this.Location.Latitude, viewport.ZoomLevel);

            int scale = -1;
            scale = (int)(this.RadiusInMeters * 2 / onePixelInMeters);
            Size newSize = Size.Empty;
            if (scale > 1)
                newSize = new Size(scale, scale);

            this.Size = newSize;

            base.ViewportChanged(viewport, action);
        }

    }

************** use the class in my code by a method ***************

public void DrawCircleOnMap()
        {
            var dbContex = new My_DBEntities();
            var data = dbContex.CarTables.Select(x => new { x.MaxRange, x.CarLat, x.CarLong }).ToList();
            foreach (var item in data)
            {
                DrawCricleOnMap element = new DrawCricleOnMap(new PointG((double)item.CarLat, (double)item.CarLong));
                //element.RadiusInMeters = int.Parse(((double)item.MaxRange).ToString());
                element.RadiusInMeters = 100;
                element.BackColor = Color.FromArgb(125, Color.LightBlue);
                element.BorderColor = Color.Red;
                radMap1.Layers["CircleLayer"].Add(element);
                //DrawCricleOnMap circle = new DrawCricleOnMap(new PointG((double)item.CarLat, (double)item.CarLong))
                //{
                //    RadiusInMeters=int.Parse("200")
                //};
                //radMap1.Layers["CircleLayer"].Add(element);
            }
        }