If, after the initial twenty-four (24) month period of service, and subsequent 12 month periods of service, Medical Center does not provide GKF with a reasonable economic justification to continue providing Gamma Knife services hereunder, then and in that event GKF shall have the option of terminating this Agreement upon the giving of written notice to Medical Center of said termination not less than ninety (90) days prior to GKF's designated termination date.