An irradiation treatment planning method constituted of: controlling a patient support member to rotate about a first axis by an initial rotation angle; imaging the patient; receiving treatment prescriptions; and responsive to the patient image, the treatment prescriptions and allowable ranges of rotation about at least two orthogonal axes, determining an irradiation treatment plan, wherein in the event that the irradiation treatment plan does not meet the treatment prescriptions, the method further comprises: responsive to the patient image, the treatment prescriptions and the allowable rotation ranges, determining rotation angles of the patient support member about the first axis; for each rotation angle, controlling the patient support member to rotate about the first axis by the rotation angle and imaging the patient; and for each rotation angle, determining an irradiation treatment plan portion responsive to the patient image, the treatment prescriptions and the allowable rotation ranges.