A method for routine monitoring and quality assurance of field asymmetry of high energy circular radiation beam producing equipment. The quality assurance process of field symmetry for devices such as stereotactic radiosurgery (SRS) systems is simplified by directly measuring the integration of the half-beam profile. The method of the invention provides that the field symmetry is obtained by positioning the tip of an ion chamber, with a collecting length approximately half the diameter of the beam, at the central axis of the beam, and rotating the ion chamber at varying angular positions, acquiring and comparing readings at desired angular positions. Each pair of readings from positions 180 degrees opposed from each other, are plugged into the equation, Asymmetry=2(R1-R2)/(R1+R2) to compute asymmetry.