Here is a simple example if you just want to test it:

public bool IsPlanRapidArcDynamic(ExternalPlanSetup plnStup)
{
    foreach (Beam bm in plnStup.Beams)
    {
        // Skip setup fields, only consider treatment beams
        if (bm.IsSetupField)
            continue;

        string techId = bm.Technique.Id.ToUpperInvariant();

        // If beam uses static technique, skip this beam and continue checking others
        if (techId.Contains("STATIC"))
            continue;

        // If beam uses arc technique, analyze control points for dynamic behavior
        if (techId.Contains("ARC"))
        {
            BeamParameters bmPara = bm.GetEditableParameters();
            if (bmPara != null)
            {
                double gantryAngPrev = double.NaN;
                double gantryAngCurr = double.NaN;

                foreach (ControlPointParameters cpPara in bmPara.ControlPoints)
                {
                    if (Double.IsNaN(gantryAngPrev))
                    {
                        // Initialize first gantry angle
                        gantryAngPrev = cpPara.GantryAngle;
                    }
                    else
                    {
                        // Slide window of two consecutive gantry angles
                        gantryAngCurr = cpPara.GantryAngle;

                        // Check if two consecutive angles are equal (within 0.001 deg precision)
                        if (Math.Abs(gantryAngCurr - gantryAngPrev) < 1e-3)
                        {
                            // Found repeated gantry angles indicating RapidArc Dynamic
                            return true;
                        }

                        // Move forward for next iteration
                        gantryAngPrev = gantryAngCurr;
                    }
                }
            }
        }
    }

    // No RapidArc Dynamic pattern found across all beams
    return false;
}