C# exiting while loop in the case of empty parameter.

I've been working on a script that finds points on two lines based a specific area

Currently the way I am getting the points are by intersecting a vertical plane from the point onto the other line. The problem is the projection continues even when the lines stop. The only stop parameter is the max vertical distance between top and bottom line.

Is there a way to terminate the loop by checking there no intersection is happening either through a empty parameter check or something like that?

This is the loop code

List< Point3d > bottoms = new List<Point3d>();
List< Point3d > tops = new List<Point3d>();
Listspan style="color: #3366ff;">double > horiz = new Listspan style="color: #3366ff;">double >();
Listspan style="color: #3366ff;">double > vert = new Listspan style="color: #3366ff;">double >();

int lastVert = 0;
int lastHoriz = 8500;
double lastParam = 0;

while(maxVert > lastVert && minHoriz < lastHoriz ) {
Point3d start = lineB.PointAt(lastParam);
Plane yz = new Plane(start, Vector3d.XAxis);
double param = 0;
Rhino.Geometry.Intersect.Intersection.LinePlane(lineA, yz, out param);
Point3d proj = lineA.PointAt(param);
double dist = start.DistanceTo(proj);
int intdist = (int) Math.Floor((dist / (double) step)) * step;
double length = (area / dist);
int intlength = (int) Math.Round((length / (double) roundfactor), MidpointRounding.AwayFromZero) * roundfactor;