**Exhibit 10.56****AGREEMENT TO PURCHASE GAMMA KNIFE PERFEXION UNIT**          This AGREEMENT TO PURCHASE GAMMA KNIFE PERFEXION UNIT (this “Agreement”) is dated effective asof the 7th day of May, 2007, and is entered into between GK FINANCING, LLC, a California limitedliability company (“GKF”), and The Regents of the University of California, a Californiacorporation (“University”), with reference to the following facts:**RECITALS**          A. Reference is made to a certain Lease Agreement for a Gamma Knife Unit (the “OriginalLease”) which was dated July 6, 1990, but which first became effective on September 17, 1991,between University and American Shared Hospital Services, a California corporation (“ASHS”).          B. Concurrently with the execution of this Agreement, the Original Lease is being furtheramended pursuant to a certain Amendment Number Five to Lease Agreement for a Gamma Knife Unit,between University and GKF (the “Fifth Amendment”). The Original Lease, as amended by the FifthAmendment and all other prior amendments, is referred to herein as the “Lease.”          C. Pursuant to the Fifth Amendment, the existing Leksell Gamma Knife, Model 4C (the “Model4C”) that is currently being leased by GKF to University pursuant to the Lease will be replacedwith a Leksell Gamma Knife Perfexion unit. GKF intends to trade-in the Model 4C to Elekta, Inc.(“Elekta”) to acquire the Leksell Gamma Knife Perfexion unit (the “Perfexion”) as described in thePurchase Agreement (USBU00001787) between GKF and Elekta (the “Elekta Purchase Agreement”).Concurrently, the Perfexion will be purchased by University from GKF pursuant to the terms of thisAgreement.          NOW THEREFORE, for valuable consideration, the receipt and sufficiency of which areacknowledged, the parties hereby amend the Lease as follows:**1.** **Purchase and Sale of the Perfexion****.** a. Purchase and Sale. Effective upon the payment in full to GKF of the“Purchase Price” and all “Taxes” (as defined below) pertaining to the Perfexion, orwithin five (5) days following the transfer of free and clear title to GKF by Elekta ofthe Perfexion, whichever occurs later (the “Transfer Date”), GKF shall sell, assign,transfer and convey to University, and University shall purchase and acquire thePerfexion from GKF, free and clear of all liens, encumbrances and adverse claims. Onthe Transfer Date, GKF shall deliver to University a duly executed bill of sale insubstantially the form set forth on Exhibit “A” attached hereto.  b. Purchase Price. The purchase price (the “Purchase Price”) for thePerfexion shall be * , plus all Taxes. The Purchase Price shall be paid by Universityas follows:
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 i. * shall be paid by University to GKF upon the issuance ofUniversity’s purchase order.  ii. * shall be paid by University to GKF not later than five (5)days prior to the expected date on which the Perfexion is shipped by Elekta orits affiliate, which shipment date is presently anticipated to be on or aboutApril 30, 2007.  iii. The balance of the Purchase Price shall be paid by Universityto GKF upon the successful completion of the “Installation Test Protocol” (asdefined in the Elekta Purchase Agreement) pertaining to the Perfexion(presently anticipated to be in the summer or fall of 2007). c. Taxes and Import Fees. University shall be responsible for (i) anysales and use taxes levied by any state or political subdivision thereof which maybecome due and owing by reason of the sale of the Perfexion hereunder, (ii) all customsand other charges with respect to the importation of the Perfexion (including theCobalt Supply) or any component thereof into the United States (collectively, “Taxes”).  d. LGK Agreement. On or before March 30, 2007, University shall enterinto a LGK Agreement with Elekta (previously submitted to University under separatecover) to secure an installation date for the Perfexion in the summer or fall of 2007.  e. Installation and Removal Costs. University shall be responsible forall insurance, rigging and positioning, and site preparation and modificationspertaining to the installation of the Perfexion and the de-installation and removal ofthe Model 4C. Pursuant to the Elekta Purchase Agreement, Elekta, and not GKF, shall beresponsible for de-installing the cobalt supply from the Model 4C, removing the Model4C, and installing new cobalt supply into the Perfexion, all at Elekta’s cost, butexcluding rigging and positioning, and site preparation and modifications related tothe Cobalt-60 loader which will be the responsibility of University. GKF shall have noliability with respect to any actions, errors or omissions on the part of Elekta and/orUniversity, and GKF makes no representations, warranties or guarantees concerningdelivery of the Perfexion to the Site or the actual date thereof..  f. Licenses and Permits. University shall obtain in a timely fashion alllicenses, permits, approvals and authorizations for a summer/fall 2007 installationdate in connection with the installation, charging, testing and use of the Perfexion,and the unloading of the cobalt supply from the Model 4C (the “Permits”).  g. Assignment of Elekta Purchase Agreement. Pursuant to the terms of acertain Assignment and Novation Agreement to be executed by the parties in the formattached hereto as Exhibit “B”, GKF shall assign to University, and University shallaccept and assume, all of GKF’s rights, duties and obligations under the
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   Elekta Purchase Agreement, including, without limitation, any and all warranties andthe Repair and Service Agreement pertaining to the Perfexion, but excluding thepurchase price set forth in the Elekta Purchase Agreement.  h. Trade-in of Model 4C. Title to the Model 4C shall be retained solelyby GKF, but will be traded-in by GKF to Elekta for the Perfexion. The Purchase Pricefor the Perfexion as set forth above reflects the discounted price based on thetrade-in value of the Model 4C.  i. Risk of Loss. From and after the first delivery of the Perfexion toUniversity’s designated delivery site, the risk of loss or destruction of or damage tothe Perfexion and any portion thereof from any cause whatsoever shall be borne byUniversity.  j. No Warranties by GKF. University warrants that it shall have (a)thoroughly inspected the Perfexion, (b) determined that the Perfexion is consistentwith the size, design, capacity and manufacture selected by it, and (c) satisfieditself that to the best of its knowledge the Perfexion is suitable for University’sintended purposes and is good working order, condition and repair. GKF SUPPLIES THEPERFEXION UNDER THIS AGREEMENT IN ITS “AS IS” CONDITION. GKF, NOT BEING THEMANUFACTURER OF THE PERFEXION OR THE MANUFACTURER’S AGENT, MAKES NO WARRANTY ORREPRESENTATION, EITHER EXPRESSED OR IMPLIED, AS TO THE PERFEXION’S MERCHANTABILITY,FITNESS FOR A PARTICULAR PURPOSE OR USE, DESIGN, CONDITION, DURABILITY, CAPACITY,MATERIAL OR WORKMANSHIP OR AS TO PATENT INFRINGEMENT OR THE LIKE, AND ALL WARRANTIES,EXPRESS OR IMPLIED, ARE EXCLUDED FROM THIS TRANSACTION AND SHALL NOT APPLY TO THE GOODSSOLD. GKF SHALL NOT BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL AND/OR CONSEQUENTIALLOSSES OR DAMAGES SUFFERED BY UNIVERSITY OR BY ANY OTHER PERSON, AND UNIVERSITYEXPRESSLY WAIVES ANY RIGHT TO HOLD GKF LIABLE HEREUNDER FOR, ANY CLAIMS, DEMANDS ANDLIABILITIES ARISING OUT OF OR IN CONNECTION WITH THE DESIGN, MANUFACTURE, POSSESSION OROPERATION OF THE PERFEXION, INCLUDING INJURY TO PERSONS OR PROPERTY RESULTING FROM THEFAILURE OF, DEFECTIVE OR FAULTY DESIGN, OPERATION, CONDITION, SUITABILITY OR USE OF THEPERFEXION. THE PARTIES AGREE THAT, TO THE EXTENT REQUIRED BY LAW, THE DISCLAIMERSCONTAINED HEREIN ARE “CONSPICUOUS” DISCLAIMERS FOR THE PURPOSE OF ANY LAW, RULE ORORDER. As between GKF and University, University shall bear all risks with respect tothe foregoing. All warranty or other similar claims with respect to the Perfexionshall be made by University solely and exclusively against any the manufacturers,suppliers or other third parties, but shall in no event be asserted against GKF. Inthis regard, University shall have the non-exclusive right, at University sole cost andexpense, to enforce all warranties, agreements or representations, if any,
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   which may have been made by the manufacturers, suppliers or other third partiesregarding the Perfexion to GKF or University. GKF shall not be responsible for thedelivery, installation or operation of the Perfexion or for any delay or inadequacyof any or all of the foregoing.**2.** **Conditions Precedent****.**The effectiveness of this Agreement is subject to all of thefollowing conditions: a. The Fifth Amendment shall have been executed by University and GKF.  b. University shall not be in breach of the Lease, and no act or omission shallhave occurred which, with the giving of notice and/or the passage of time, wouldconstitute such a breach under the Lease.  c. At all times prior to the Equipment Transition Date (as defined in the FifthAmendment), procedures will continue to be scheduled on the Model 4C in the ordinarycourse of business.**3.** **Miscellaneous****.** a. Captions. The captions and paragraph headings used herein are forconvenience only and shall not be used in construing or interpreting this Agreement.  b. Binding Effect. This Agreement shall be binding upon and inure to thebenefit of the parties hereto and their respective permitted successors and assigns.University shall not assign this Agreement or any of its rights hereunder without theprior written consent of GKF. An assignment or sublease shall not relieve Universityof any liability for performance of this Agreement. Any purported assignment madewithout GKF’s prior written consent shall be null, void and of no force or effect.  c. Agreement to Perform Necessary Acts. Each party agrees to perform anyfurther acts and execute and deliver any further documents which may be reasonablynecessary or otherwise reasonably required to carry out the provisions of thisAgreement.  d. Validity. If for any reason any clause or provision of this Agreement,or the application of any such clause or provision in a particular context or to aparticular situation, circumstance or person, should be held unenforceable, invalid orin violation of law by any court or other tribunal of competent jurisdiction, then theapplication of such clause or provision in contexts or to situations, circumstances orpersons other than that in or to which it is held unenforceable, invalid or inviolation of law shall not be affected thereby, and the remaining clauses andprovisions hereof shall nevertheless remain in full force and effect.  e. Attorney’s Fees and Costs. In the event of any action, arbitration orother proceedings between or among the parties hereto with respect to this Agreement,the non prevailing party or parties to such action, arbitration or proceedings shall
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   pay to the prevailing party or parties all costs and expenses, including reasonableattorneys’ fees, incurred in the defense or prosecution thereof by the prevailingparty or parties. The party which is a “prevailing party” shall be determined bythe arbitrator(s) or judge(s) hearing the matter and shall be the party who isentitled to recover his, her or its costs of suit, whether or not the matterproceeds to a final judgment, decree or determination. A party not entitled torecover his, her or its costs of suit shall not recover attorneys’ fees. If aprevailing party or parties shall recover a decision, decree or judgment in anyaction, arbitration or proceeding, the costs and expenses awarded to such party maybe included in and as part of such decision, decree or judgment.  f. Entire Agreement; Amendment. This Agreement together with the Exhibitsattached hereto constitutes the full and complete agreement and understanding betweenthe parties hereto concerning the subject matter hereof and shall supersede any and allprior written and oral agreements with regard to such subject matter. This Agreementmay be modified or amended only by a written instrument executed by all of the partieshereto.  g. Governing Law. This Agreement shall be interpreted and enforced inaccordance with the internal laws, and not the law of conflicts, of the State ofCalifornia applicable to agreements made and to be performed in that State.  h. Ambiguities. The general rule that ambiguities are to be construedagainst the drafter shall not apply to this Agreement. In the event that any provisionof this Agreement is found to be ambiguous, each party shall have an opportunity topresent evidence as to the actual intent of the parties with respect to such ambiguousprovision.  i. Non-Waiver. No failure or delay by a party to insist upon the strictperformance of any term, condition, covenant or agreement of this Agreement, or toexercise any right, power or remedy hereunder or under law or consequent upon a breachhereof or thereof shall constitute a waiver of any such term, condition, covenant,agreement, right, power or remedy or of any such breach or preclude such party fromexercising any such right, power or remedy at any later time or times.  j. Force Majeure. Failure to perform by either party will be excused inthe event of any delay or inability to perform its duties under this Agreement directlyor indirectly caused by conditions beyond its reasonable control, including, withoutlimitation, fires, floods, earthquakes, snow, ice, disasters, acts of God, accidents,riots, wars, operation of law, strikes, governmental action or regulations, shortagesof labor, fuel, power, materials, manufacturer delays or transportation problems.Notwithstanding the foregoing, all parties shall make good faith efforts to performunder this Agreement in the event of any such circumstance. Further, once such anevent is resolved, the parties shall again perform their respective obligations underthis Agreement.
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          IN WITNESS WHEREOF, the parties have executed this Agreement effective as of the date firstwritten above.           **GKF:**   **University:**             **GK FINANCING, LLC**   **THE REGENTS OF THE UNIVERSITY OFCALIFORNIA**             By: /s/ Ernest A. Bates, M.D. Ernest A. Bates, M.D.   By: /s/ Ken Jones Ken Jones    Policy Committee Member     Chief Financial Officer  
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Exhibit “B”ASSIGNMENT AND NOVATION AGREEMENT
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**ASSIGNMENT AND NOVATION AGREEMENT**This agreement is entered into on the 9th day of May 2007 by and between Elekta, Inc., 4775Peachtree Industrial Boulevard, Building 300, Suite 300, Norcross, Georgia 30092, (hereinafterreferred to as ”Elekta”), GK Financing, LLC, 4 Embarcadero Center, suite 2370, San Fransisco, CA94111-5994 (hereinafter referred to as ”GKF”) and The Regents of the University of California, aCalifornia corporation, 500 Parnassus Avenue, San Francisco, CA 94143 (hereinafter referred to as”UCSF”)**WITNESSETH****WHEREAS**Elekta and GKF have entered into Purchase Agreement USBU00001787 for the purchase of oneLeksell Gamma Knife Perfexion unit (the ”Perfexion”) for delivery to UCSF. Such PurchaseAgreement, together with all exhibits, including the Repair Service Agreement is hereinafterreferred to as the ”Elekta Purchase Agreement.”**WHEREAS**UCSF and GKF have entered into a certain Agreement To Purchase Gamma Knife Perfexion Unit(the ”UCSF Purchase Agreement”) pursuant to which UCSF will purchase the Perfexion from GKF.**WHEREAS**the parties have agreed that, on the ”Effective Date” (as defined below), (i) all of therights and obligations of GKF under the Elekta Purchase Agreement (but excluding the purchase priceset forth in the Elekta Purchase Agreement) shall be assigned from GKF to UCSF, and (ii) GKF shallbe discharged and released from the performance of all of its obligations set forth in the ElektaPurchase Agreement.**WHEREAS**Clause 8.1 of the Elekta Purchase Agreement provides that no such assignment can take placewithout the prior written consent of Elekta,**NOW, THEREFORE**, for valuable consideration, the receipt and sufficiency of which are acknowledged,and in order to affect and confirm agreement with such an assignment and novation, the Parties haveagreed as follows.  **1.** **Assignment.**Effective as of the ”Effective Date,” GKF hereby transfers and assigns alloutstanding its rights and obligation under the Elekta Purchase Agreement (but excludingthe purchase price set forth in the Elekta Purchase Agreement), and UCSF hereby acceptsthis transfer and assumes all such outstanding rights and obligations under the ElektaPurchase Agreement. Effective as of the ”Effective Date,” GKF shall be released from allrights, duties and obligations with respect to the Elekta Purchase Agreement, and UCSFagrees to reimburse GKF for and hold GKF harmless against any obligation to perform any ofthe assigned duties and obligations under the Elekta Purchase Agreement. As used herein,the ”Effective Date” shall mean the date on which Elekta receives the
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   final payment due under the Elekta Purchase Agreement from GKF. The parties acknowledge thattransfer of title to GKF will take place as per the Elekta Purchase Agreement.  **2.** **Novation.**Elekta, GKF and UCSF each hereby agrees that, effective as of the EffectiveDate, this Agreement shall constitute a novation of the obligations of GKF under the ElektaPurchase Agreement, and any and all of the rights, duties and obligations of GKF under theElekta Purchase Agreement shall be automatically extinguished.  **3.** **Consent to assignment.**With reference to Section 8.1 of the Elekta Purchase Agreement,Elekta hereby gives its prior, written consent to the transfer as per Section 1 above.  **4.** **Effect of Amendment.**Except as explicitly set forth in this Amendment, and subsequentto the execution hereof, the terms of the Elekta Purchase Agreement shall remain in fullforce and effect between Elekta and UCSF.           **IN WITNESS WHEREOF**, the duly authorized representative of the parties hereto have set theirhands and seals, the day and year first above written.           **GK FINANCING, LLC**   **ELEKTA, INC.**             By: