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                                                                  EXHIBIT 10.17

Confidential material appearing in this document has been omitted and filed 
separately with the Securities and Exchange Commission in accordance with Rule 
24b-2, promulgated under the Securities and Exchange Act of 1934, as amended. 
Omitted information has been replaced with asterisks.


                                    ADDENDUM

                    TO LEASE AGREEMENT FOR A GAMMA KNIFE UNIT


        This ADDENDUM TO LEASE AGREEMENT FOR A GAMMA KNIFE UNIT (this
"Addendum") is effective December 1, 1998 between Hoag Memorial Hospital
Presbyterian, a California Corporation ("Hospital"), and GK Financing, LLC, a
California limited liability company ("GKF").

                                    RECITALS

        WHEREAS, on October 31, 1996, GKF and Hospital executed a Lease
Agreement for a Gamma Knife Unit (the "Original Lease");

        WHEREAS, the parties desire to amend the terms and provisions of the
Original Lease as set forth herein.

        NOW, THEREFORE, in consideration of the mutual covenants and agreements
set forth herein, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties agree as follows:

                                    AGREEMENT

        1. DEFINED TERMS. Unless otherwise defined herein, the capitalized terms
used herein shall have the same meaning set forth in the Original Lease.

        2. *

        3. MARKETING. Hospital and GKF agree to cooperatively market Gamma Knife
services at the Hoag/UCI Gamma Knife center.

        4. TERM OF AMENDMENT. This addendum shall be in effect for a one year
period, December 1, 1998, though November 30, 1999.

        5. FULL FORCE AND EFFECT. Except as otherwise amended hereby or provided
herein, all of the terms and provisions of the Original Lease shall remain in
full force and effect.


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        IN WITNESS WHEREOF, the parties have executed this Addendum effective as
of the date first written above.

               "HOSPITAL"                   Hoag Memorial Hospital Presbyterian



               BY:                          /s/ MICHAEL D. STEPHENS
                                            ------------------------------------
                                            MICHAEL D. STEPHENS, PRESIDENT


               "GKF"                        GK Financing, LLC



               BY:                          /s/ CRAIG K. TAGAWA
                                            ------------------------------------
                                            Craig K. Tagawa, 
                                            Chief Executive Officer