**Exhibit
      10.1**





**THIRD
      A** **MENDMENT**


**TO**


**LOAN
      AND SECURITY AGREEMENT**





**THIS
      THIRD AMENDMENT** **to
      Loan and Security Agreement** (this **** “Amendment”)
      is entered into on August 24, 2007, by and between




SILICON
      VALLEY BANK (“Bank”)




and
      the
      following (collectively, jointly and severally, the "Borrower") whose address
      is
      20200 Sunburst Street, Chatsworth, California 91311:




NORTH
      AMERICAN SCIENTIFIC ,
      INC., a
      Delaware corporation (“NASI”);




NORTH
      AMERICAN SCIENTIFIC, INC., a California corporation (“NASI-CA”);
      and




NOMOS
      CORPORATION, a Delaware corporation (“NOMOS”).






**Recitals**




**A.**  Bank
      and
      Borrower have entered into that certain Loan and Security Agreement, with an
      Effective Date of October 5, 2005 (as the same has been, and may hereafter
      from
      time to time be amended, modified, supplemented or restated, the “Loan
      Agreement”).




**B.**  Bank
      has
      extended credit to Borrower for the purposes permitted in the Loan Agreement.




**C.**  The
      parties desire to amend the Loan Agreement as herein set forth.




**Agreement**




**Now,
      Therefore,** in
      consideration of the foregoing recitals and other good and valuable
      consideration, the receipt and adequacy of which are hereby acknowledged, and
      intending to be legally bound, the parties hereto agree as follows:




**1.**  **Definitions.** Capitalized terms used but not defined in this Amendment shall have the meanings
      given to them in the Loan Agreement.




**2.**  **Amendments
      to Loan Agreement.** The
      Loan
      Agreement is hereby amended as follows, effective as of the date
      hereof:




1




**2.1**  **Limited
      Waiver Regarding Minimum Tangible Net Worth Financial Covenant
      Defaults.**  Borrower
      has advised Bank that
      Borrower has failed to comply with the Minimum Tangible Net Worth Financial
      Covenant set forth in Section 5 of the Amended and Restated Schedule 2 to Loan
      and Security Agreement for the compliance periods ending May 31, 2007 and June
      30, 2007 (the “Minimum TNW Covenant Defaults”). Bank and Borrower agree that the
      Borrower's Minimum TNW Covenant Defaults are hereby waived. It is understood
      by
      the parties hereto, however, that such waiver does not constitute a waiver
      of
      any other provision or term of the Loan Agreement or any related document,
      nor
      an agreement to waive in the future this covenant or any other provision or
      term
      of the Loan Agreement or any related document.




**2.2**  **Limited
      Waiver Regarding Partners For Growth Cross-Default.**  Borrower
      has advised Bank that Borrower has received a default letter from Partners
      for
      Growth informing the Borrower that it was in default under the Borrower’s loan
      agreement with Partners for Growth (the “PFG Loan Agreement”). The defaults
      under the PFG Loan Agreement constitute an Event of Default under the Loan
      Agreement (the “PFG Cross-Default”). Bank and Borrower agree that the Borrower's
      PFG Cross-Default is hereby waived. It is understood by the parties hereto,
      however, that such waiver does not constitute a waiver of any other provision
      or
      term of the Loan Agreement or any related document, nor an agreement to waive
      in
      the future this covenant or any other provision or term of the Loan Agreement
      or
      any related document.




**2.3**  **Modified
      Credit Limit (Addition of Bridge Loan Sublimit).** Section
      1 of the Amended and Restated Schedule 2 to Loan and Security Agreement is
      hereby amended to read as follows:






**1.** **CREDIT
      LIMIT**


(Section
      2.1.1): An
      amount
      not to exceed:





(a)
            the
                lesser of (1)**$4,000,000**at
                any one time outstanding (the “Revolving
                Line Credit Amount”)
                or (2) the sum of the following (the “Borrowing
                Base”):





(i)
            up
                to**80%**(an
                “Advance Rate”) of the amount of NASI Eligible Accounts,plus




(ii)
            up
                to**80%**(an
                “Advance Rate”) of the amount of NASI-CA Eligible Accounts,plus




(iii)
            up
                to**75%**(an
                “Advance Rate”) of the amount of NOMOS Eligible Accounts;plus





(iv)
            the
                lesser of the following (the “Bridge
                Loan Sublimit”):




2




(A)
            **$1,500,000**or





(B)
            the
                sum of:





(I)
            **20%**(an
                “Advance Rate) of the amount of NASI-CA Eligible Accounts,plus





(II)
            **100%**(an Advance Rate) of the amount of NASI-CA Accounts not deemed to
                be
                Eligible Accounts;





provided , however ,
      in no
      event shall the amount of the Bridge Loan Sublimit exceed **$750,000** until
      such time as Borrower has received a signed term sheet dated after the date
      hereof, satisfactory to Silicon in its sole discretion, for the receipt by
      Borrower of at least $10,000,000 for the issuance of additional equity
      securities of Borrower.


minus




(b) the
      sum
      of the following:





(i)
            the
                amount of all outstanding Letters of Credit (including drawn but
                unreimbursed Letters of Credit);plus





(ii)
            the
                FX Reserve; andplus




3




(iii)
            the
                aggregate amount of Cash Management Services
                utilizations.





provided , however ,
      that
      Bank shall have the right, in Bank’s discretion, to modify the above Advance
      Rates based upon the results of field audits conducted by Bank.





**Letter
      of Credit Sublimit**


**(Section
                2.1.2):**
            
            
            **$500,000**.





**Foreign
      Exchange Sublimit**


**(Section
                2.1.3):**
            
            
            **$500,000**.





**Cash
      Management Services Sublimit:**


**(Section
                2.1.4):**
            
            
            **$500,000**.





**2.4** **Modified
      Interest Rate.** Interest
      Rate set forth in Section 2 of the Amended and Restated Schedule 2 to Loan
      and
      Security Agreement is hereby amended to read as follows:




**Interest
      Rate**


(Section
      2.3(a)): A
      per
      annum rate equal to the “Prime Rate” in effect from time to time;


provided
      that if the Quick Ratio Test is not met, the interest rate applicable to the Obligations
      shall be a per annum rate equal to the “Prime Rate” in effect from time to time,
      plus 1.50% per annum; provided , however ,
      with
      respect to Obligations pertaining to
      the
      Bridge Loan Sublimit, the interest rate applicable to such Obligations shall
      be
      a per
      annum
      rate equal to the “Prime Rate” in effect from time to time, plus 4.0% per annum.
      Changes in the interest rate based on whether or not the Quick Ratio Test is
      met shall
      go
      into effect as of the first day of the month closest to the date Borrower’s financial
      statements, which show whether or not the Quick Ratio Test is met, are due, even
      if
      the delivery of the financial statements is delayed. ****




**2.5**  **Modified
      Maturity Date.** The
      Maturity Date set forth in Section 4 of the Amended and Restated Schedule 2
      to
      Loan and Security Agreement is hereby amended to read as follows:




4




**4.** **MATURITY
      DATE** ****


(Section
      13.1):  October
      3, 2007.





Notwithstanding
      the foregoing, the Maturity Date with respect to the Bridge Loan Sublimit shall
      be the earlier of (i) October 3, 2007 or (ii) the date Borrower closes the
      private investment public equity transaction of which Silicon has been advised
      by Borrower (which Borrower has informed Silicon would result in the receipt
      of
      more than $15,000,000 net cash proceeds to Borrower).





**2.6**  **Modified
      Minimum Tangible Net Worth Financial Covenant.** The
      Minimum Tangible Net Worth Financial Covenant set forth in Section 5 of the
      Amended and Restated Schedule 2 to Loan and Security Agreement is hereby amended
      to read as follows:




Minimum
      Tangible


Net
      Worth:  Borrower
      shall maintain a Tangible Net Worth of not less than $2,000,000.





**2.7**  **Exhibit
      D.** Exhibit
      D
      to the Loan Agreement, the form of Compliance Certificate, is hereby replaced
      by
      Exhibit D hereto.




**2.8**  **Warrant.** Concurrently
      herewith, Borrower shall issue to Bank a five-year Warrant to Purchase Stock
      for
      the issuance of 300,000 shares of Borrower’s common stock at the issue price set
      forth in the Warrant and on such other terms and conditions as are acceptable
      to
      Bank in its good faith business judgment.




**3.**  **Limitation
      of Amendments.**




**3.1**  The
      amendments set forth in Section 2, above, are effective for the purposes
      set forth herein and shall be limited precisely as written and shall not be
      deemed to (a) be a consent to any amendment, waiver or modification of any
      other term or condition of any Loan Document, or (b) otherwise prejudice
      any right or remedy which Bank may now have or may have in the future under
      or
      in connection with any Loan Document.




**3.2**  This
      Amendment shall be construed in connection with and as part of the Loan
      Documents and all terms, conditions, representations, warranties, covenants
      and
      agreements set forth in the Loan Documents, except as herein amended, are hereby
      ratified and confirmed and shall remain in full force and effect.




**4.**  **Representations
      and Warranties.** To
      induce Bank to enter into this Amendment, Borrower hereby represents and
      warrants to Bank as follows:




5




**4.1**  Immediately
      after giving effect to this Amendment (a) the representations and
      warranties contained in the Loan Documents are true, accurate and complete
      in
      all material respects as of the date hereof (except to the extent such
      representations and warranties relate to an earlier date, in which case they
      are
      true and correct as of such date), and (b) no Event of Default has occurred
      and is continuing;




**4.2**  Borrower
      has the corporate power and authority to execute and deliver this Amendment
      and
      to perform its obligations under the Loan Agreement, as amended by this
      Amendment;




**4.3**  The
      organizational documents of Borrower delivered to Bank on the Effective Date
      remain accurate and complete and have not been amended, supplemented or restated
      since the Effective Date and are, and continue to be, in full force and
      effect;




**4.4**  The
      execution and delivery by Borrower of this Amendment and the performance by
      Borrower of its obligations under the Loan Agreement, as amended by this
      Amendment, have been duly authorized;




**4.5**  The
      execution and delivery by Borrower of this Amendment and the performance by
      Borrower of its obligations under the Loan Agreement, as amended by this
      Amendment, do not and will not contravene (a) any law or regulation binding
      on or affecting Borrower, (b) any material agreement by which Borrower or
      its property is bound, (c) any order, judgment or decree of any court or
      other governmental or public body or authority, or subdivision thereof, binding
      on Borrower, or (d) the organizational documents of Borrower;




**4.6**  The
      execution and delivery by Borrower of this Amendment and the performance by
      Borrower of its obligations under the Loan Agreement, as amended by this
      Amendment, do not require any order, consent, approval, license, authorization
      or validation of, or filing, recording or registration with, or exemption by
      any
      governmental or public body or authority, or subdivision thereof, binding on
      either Borrower, except as already has been obtained or made; and




**4.7**  This
      Amendment has been duly executed and delivered by Borrower and is the binding
      obligation of Borrower, enforceable against Borrower in accordance with its
      terms, except as such enforceability may be limited by bankruptcy, insolvency,
      reorganization, liquidation, moratorium or other similar laws of general
      application and equitable principles relating to or affecting creditors’
rights.




**5.**  **Counterparts.** This
      Amendment may be executed in any number of counterparts and all of such
      counterparts taken together shall be deemed to constitute one and the same
      instrument.




**6.**  **Effectiveness** .
      This
      Amendment shall be deemed effective upon (a) the due execution and delivery
      to
      Bank of this Amendment by each party hereto and (b) Borrower’s payment of
      an amendment fee in an amount equal to $25,000 ($15,000 of which Borrower has
      paid to Bank and the receipt of which Bank hereby acknowledges).




[Signature
      page follows.]




6


**In
      Witness Whereof,**  the
      parties hereto have caused this First Amendment to be duly executed and
      delivered as of the date first written above.





“Borrower”:
              
              **NORTH
                AMERICAN SCIENTIFIC, INC.**
              A
                Delaware corporation
              
              
              By     
                /s/John
                B. Rush
              
              President
                or Vice President
            “Bank”:
              
              **SILICON
                VALLEY BANK**
              
              
              By    
                /s/Derek
                Brunelle
              
              
              TitleVice
                President“Borrower”:
              
              **NORTH
                AMERICAN SCIENTIFIC, INC.**
              A
                California corporation
              
              By   
                  /s/John B. Rush
                President or Vice President“Borrower”:
              
              **NOMOS
                CORPORATION**
              
              By   
                  /s/John B. Rush
                
                President
                  or
                  Vice President




7




**EXHIBIT
      D**


**COMPLIANCE
      CERTIFICATE**





TO:  SILICON
      VALLEY BANK


38
      Technology Drive, Suite 150


Irvine,
      CA 92618





FROM: North
      American Scientific, Inc .,
      a
      Delaware corporation


North
      American Scientific, Inc .,
      a
      California corporation; and


NOMOS
      Corporation ,
      a
      Delaware corporation








The
      undersigned authorized officers of each of North
      American Scientific, Inc., a Delaware corporation, North American Scientific,
      Inc., a California corporation, and NOMOS Corporation (collectively “Borrower”) certifies that under the terms and conditions of the
      Loan and Security Agreement between Borrower and Bank (the “Agreement”),
      (i) Borrower is in complete compliance for the period ending
      _______________ with all required covenants except as noted below and
      (ii) all representations and warranties in the Agreement are true and
      correct in all material respects on this date, provided that any representations
      and warranties expressly referring to another date are true and correct in
      all
      material respects as of such other date. In
      addition, the undersigned certifies that (1) Borrower has timely filed all
      required tax returns and paid, or made adequate provision to pay, all material
      taxes, except those being contested in good faith with adequate reserves under
      GAAP and (2) no liens have been levied or claims made against Borrower relating
      to unpaid employee payroll or benefits which Borrower has not previously
      notified in writing to Bank. Attached
      are the required documents supporting the certification. The Officer certifies
      that these are prepared in accordance with Generally Accepted Accounting
      Principles (GAAP) consistently applied from one period to the next except as
      explained in an accompanying letter or footnotes. The Officer acknowledges
      that
      no borrowings may be requested at any time or date of determination that
      Borrower is not in compliance with any of the terms of the Agreement, and that
      compliance is determined not just at the date this certificate is
      delivered.





**Please
      indicate compliance status by circling Yes/No under “Complies”
column.**





**Reporting
                Covenant**
            **Required**
            
            **Complies**Monthly
                financial statements + CC
            Monthly
                within 30 days
            
            YesNoN/AQuarterly
                Reports on Form 10-Q
            Within
                5 days of filing to the SEC
            
            YesNoN/AAnnual
                Report on Form 10-K (Audited)
            FYE
                within 5 days of filing with the SEC
            
            YesNoN/AA/R
                & A/P Agings
            Monthly
                w/in 15 days
            
            YesNoN/AWeekly
                transactions reports and schedules of collections (when required
                under
                Loan Agreement)
            Weekly
            
            YesNoN/AMonthly
                reconciliations of A/R agings, Transaction Reports and general ledger
            Monthly
                within 30 days
            
            YesNoN/A




8




**Financial
                Covenant**
            **Required**
            **Actual**
            **Complies**Maintain
                at all times and measured on a monthly basis: Minimum Tangible Net
                Worth
            $2,000,000
            $______________
            YesNoN/A





Borrower
      only has deposit accounts located at the following institutions:
      ___________________.





Has
      Borrower filed any new Trademark, Patent or Copyright applications?  Yes
      /
      No


(If
      “yes”, please list below and complete the attached Addendum to Intellectual
      Property Security Agreement)





Trademarks:
      ___________________________________________________





Patents:
      _______________________________________________________





Copyrights:
      ______________________________________________________





**Comments
      Regarding Exceptions:** See
      Attached.




Sincerely,
              **BANK
                  USE ONLY****North
                  American Scientific, Inc.**
              Received
                  by:  ________________________**A Delaware
                corporation**
              AUTHORIZED
                  SIGNERDate:
                  ______________________________By: ______________________________
              Verified: ____________________________Authorized
                  Signer
              AUTHORIZED
                  SIGNER**North
                  American Scientific, Inc.**
              Date: ______________________________**A California
                corporation**Compliance
                  Status:  Yes 
                  NoBy: ______________________________Authorized
                  Signer
  9
  **NOMOS
                Corporation****A
                  Delaware corporation**By: ______________________________Authorized
                  Signer_________________________________Date




10





**THIS
      WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE
      SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR THE SECURITIES LAWS OF ANY
      STATE AND, EXCEPT AND PURSUANT TO THE PROVISIONS OF ARTICLE 5 BELOW, MAY NOT
      BE
      OFFERED, SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED UNLESS AND
      UNTIL
      REGISTERED UNDER SAID ACT AND APPLICABLE STATE SECURITIES LAW OR, IN THE OPINION
      OF LEGAL COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE ISSUER OF THESE
      SECURITIES, SUCH OFFER, SALE OR TRANSFER, PLEDGE OR HYPOTHECATION IS EXEMPT
      FROM
      REGISTRATION.**





**WARRANT
      TO PURCHASE STOCK**




Company:
              **NORTH
                  AMERICAN SCIENTIFIC, INC.**,
                  a
                  Delaware corporationNumber
                  of Shares:
              300,000Class
                  of Stock:
              Common
                  StockWarrant
                  Price:
              The
                  lower of: (i) the closing price of the Company’s commonstock
                  on the date the Company’s Board of Directors approves
                  theissuance
                  of this Warrant or (ii) the closing price of the Company’scommon
                  stock on the Issue Date.Issue
                  Date:
              August
                  24, 2007Expiration
                  Date:
              August
                24,
                2012




THIS
      WARRANT CERTIFIES THAT, for the agreed upon value of $1.00 and for other good
      and valuable consideration, SILICON VALLEY BANK ("Holder") is entitled to
      purchase the number of fully paid and nonassessable shares of the common stock,
      $0.01 par value per share (the "Shares") of the company (the "Company") at
      the
      Warrant Price, all as set forth above and as adjusted pursuant to Article 2
      of
      this Warrant, subject to the provisions and upon the terms and conditions set
      forth in this Warrant.





ARTICLE
      1. EXERCISE .





1.1  Method
      of Exercise .
      Holder
      may exercise this Warrant by delivering a duly executed Notice of Exercise
      in
      substantially the form attached as Appendix 1 to the principal office of the
      Company. Unless Holder is exercising the conversion right set forth in Article
      1.2, Holder shall also deliver to the Company a check, wire transfer (to an
      account designated by the Company), or other form of payment acceptable to
      the
      Company for the aggregate Warrant Price for the Shares being
      purchased.





1.2  Conversion
      Right .
      In lieu
      of exercising this Warrant as specified in Article 1.1, Holder may from time
      to
      time convert this Warrant, in whole or in part, into a number of Shares
      determined by dividing (a) the aggregate fair market value of the Shares or
      other securities otherwise issuable upon exercise of this Warrant minus the
      aggregate Warrant Price of such Shares by (b) the fair market value of one
      Share. The fair market value of the Shares shall be determined pursuant to
      Article 1.3.




11




1.3  Fair
      Market Value .
      If the
      Company’s common stock is traded in a public market and the Shares are common
      stock, the fair market value of each Share shall be the closing price of a
      Share
      reported for the business day immediately before Holder delivers its Notice
      of
      Exercise to the Company. . If the Company’s common stock is not traded in a
      public market, the Board of Directors of the Company shall determine fair market
      value in its reasonable good faith judgment.





1.4  Delivery
      of Certificate and New Warrant .
      Promptly after Holder exercises or converts this Warrant and, if applicable,
      the
      Company receives payment of the aggregate Warrant Price, the Company shall
      deliver to Holder certificates for the Shares acquired and, if this Warrant
      has
      not been fully exercised or converted and has not expired, a new Warrant
      representing the Shares not so acquired.





1.5  Replacement
      of Warrants .
      On
      receipt of evidence reasonably satisfactory to the Company of the loss, theft,
      destruction or mutilation of this Warrant and, in the case of loss, theft or
      destruction, on delivery of an indemnity agreement reasonably satisfactory
      in
      form and amount to the Company or, in the case of mutilation on surrender and
      cancellation of this Warrant, the Company shall execute and deliver, in lieu
      of
      this Warrant, a new warrant of like tenor.





1.6  Treatment
      of Warrant Upon Acquisition of Company .





1.6.1  " Acquisition ".
      For
      the purpose of this Warrant, "Acquisition" means any sale, license, or other
      disposition of all or substantially all of the assets of the Company, or any
      reorganization, consolidation, or merger of the Company where the holders of
      the
      Company's securities before the transaction beneficially own less than 50%
      of
      the outstanding voting securities of the surviving entity after the
      transaction.





1.6.2
            Treatment
                of Warrant at Acquisition.




A) Upon
      the
      written request of the Company, Holder agrees that, in the event of an
      Acquisition that is not an asset sale and in which the sole consideration is
      cash, either (a) Holder shall exercise its conversion or purchase right under
      this Warrant and such exercise will be deemed effective immediately prior to
      the
      consummation of such Acquisition or (b) if Holder elects not to exercise the
      Warrant, this Warrant will expire upon the consummation of such Acquisition.
      The
      Company shall provide the Holder with written notice of its request relating
      to
      the foregoing (together with such reasonable information as the Holder may
      request in connection with such contemplated Acquisition giving rise to such
      notice), which is to be delivered to Holder not less than ten (10) days prior
      to
      the closing of the proposed Acquisition.




B) Upon
      the
      written request of the Company, Holder agrees that, in the event of an
      Acquisition that is an “arms length” sale of all or substantially all of the
      Company’s assets (and only its assets) to a third party that is not an Affiliate
      (as defined below) of the Company (a “True Asset Sale”), either (a) Holder shall
      exercise its conversion or purchase right under this Warrant and such exercise
      will be deemed effective immediately prior to the consummation of such
      Acquisition or (b) if Holder elects not to exercise the Warrant, this Warrant
      will continue until the Expiration Date if the Company continues as a going
      concern following the closing of any such True Asset Sale. The Company shall
      provide the Holder with written notice of its request relating to the foregoing
      (together with such reasonable information as the Holder may request in
      connection with such contemplated Acquisition giving rise to such notice),
      which
      is to be delivered to Holder not less than ten (10) days prior to the closing
      of
      the proposed Acquisition.




12




C) Upon
      the
      closing of any Acquisition other than those particularly described in
      subsections (A) and (B) above, the successor entity shall assume the obligations
      of this Warrant, and this Warrant shall be exercisable for the same securities,
      cash, and property as would be payable for the Shares issuable upon exercise
      of
      the unexercised portion of this Warrant as if such Shares were outstanding
      on
      the record date for the Acquisition and subsequent closing. The Warrant Price
      and/or number of Shares shall be adjusted accordingly.




As
      used
      herein “ Affiliate ”
shall
      mean any person or entity that owns or controls directly or indirectly ten
      (10)
      percent or more of the stock of Company, any person or entity that controls
      or
      is controlled by or is under common control with such persons or entities,
      and
      each of such person’s or entity’s officers, directors, joint venturers or
      partners, as applicable.





ARTICLE
      2. ADJUSTMENTS
      TO THE SHARES .





2.1  Stock
      Dividends, Splits, Etc .
      If the
      Company declares or pays a dividend on the Shares payable in common stock,
      or
      other securities, then upon exercise of this Warrant, for each Share acquired,
      Holder shall receive, without cost to Holder, the total number and kind of
      securities to which Holder would have been entitled had Holder owned the Shares
      of record as of the date the dividend occurred. If the Company subdivides the
      Shares by reclassification or otherwise into a greater number of shares or
      takes
      any other action which increase the amount of stock into which the Shares are
      convertible, the number of shares purchasable hereunder shall be proportionately
      increased and the Warrant Price shall be proportionately decreased, but the
      aggregate purchase price payable for the total number of shares purchasable
      under this Warrant (as adjusted) shall remain the same. If the outstanding
      shares are combined or consolidated, by reclassification or otherwise, into
      a
      lesser number of shares, the Warrant Price shall be proportionately increased
      (but the aggregate purchase price payable for the total number of Shares
      purchasable under this Warrant, as adjusted, shall remain the same), and the
      number of Shares shall be proportionately decreased.





2.2  Reclassification,
      Exchange, Combinations or Substitution .
      Upon
      any reclassification, exchange, substitution, or other event that results in
      a
      change of the number and/or class of the securities issuable upon exercise
      or
      conversion of this Warrant, Holder shall be entitled to receive, upon exercise
      or conversion of this Warrant, the number and kind of securities and property
      that Holder would have received for the Shares if this Warrant had been
      exercised immediately before such reclassification, exchange, substitution,
      or
      other event. The Company or its successor shall promptly issue to Holder an
      amendment to this Warrant setting forth the number and kind of such new
      securities or other property issuable upon exercise or conversion of this
      Warrant as a result of such reclassification, exchange, substitution or other
      event that results in a change of the number and/or class of securities issuable
      upon exercise or conversion of this Warrant. The amendment to this Warrant
      shall
      provide for adjustments which shall be as nearly equivalent as may be
      practicable to the adjustments provided for in this Article 2 including, without
      limitation, adjustments to the Warrant Price (but not to the aggregate purchase
      price payable for the total number of Shares purchasable under this Warrant
      (as
      adjusted), which shall remain the same) and to the number of securities or
      property issuable upon exercise of the new Warrant. The provisions of this
      Article 2.2 shall similarly apply to successive reclassifications, exchanges,
      substitutions, or other events.




13




2.3  Adjustments
      for Diluting Issuances .
      In the
      event the Company, within one year of the date hereof should issue additional
      shares of Common Stock, or options, warrants or other securities (including
      units comprising shares of Common Stock and other securities or rights)
      convertible into Common Stock (collectively, “Convertible Securities”), at a per
      share Value attributable to Common Stock less than the Warrant Price in effect
      immediately prior to such issuance, the Warrant Price shall be reduced to such
      lower Value; provided however, that no adjustment shall be made with respect
      to
      issuances by the Company of up to an aggregate of 6,968,978 shares of Common
      Stock at not less than the then fair market value per share of Common Stock
      to
      its officers, directors and employees pursuant to its 2006 Stock Plan, 2000
      Employee Stock Purchase Plan and 2003 Non-Employee Directors’ Equity
      Compensation Plan and any other employee incentive plans approved by the
      Company’s stockholders. In addition to a reduction in the Warrant Price as
      aforesaid, the number of shares issuable upon exercise of this Warrant shall
      be
      proportionately increased (such that the percentage of the total equity
      obtainable upon exchange remains the same). For purposes hereof, the term
“Value” shall take into account the effective price of any security which is
      comprised of Common Stock (or Convertible Securities) and other securities
      or
      rights, such as, for example, a unit which includes Common Stock and a warrant
      to purchase Common Stock, a Convertible Security or right (such as a stock
      appreciation right).





2.4  No
      Impairment .
      The
      Company shall not, by amendment of its Certificate of Incorporation or through
      a
      reorganization, transfer of assets, consolidation, merger, dissolution, issue,
      or sale of securities or any other voluntary action, avoid or seek to avoid
      the
      observance or performance of any of the terms to be observed or performed under
      this Warrant by the Company, but shall at all times in good faith assist in
      carrying out of all the provisions of this Article 2 and in taking all such
      action as may be necessary or appropriate to protect Holder's rights under
      this
      Article against impairment.





2.5  Fractional
      Shares .
      No
      fractional Shares shall be issuable upon exercise or conversion of this Warrant
      and the number of Shares to be issued shall be rounded down to the nearest
      whole
      Share. If a fractional share interest arises upon any exercise or conversion
      of
      the Warrant, the Company shall eliminate such fractional share interest by
      paying Holder the amount computed by multiplying the fractional interest by
      the
      fair market value of a full Share.





2.6  Certificate
      as to Adjustments .
      Upon
      each adjustment of the Warrant Price, the Company shall promptly notify Holder
      in writing, and, at the Company’s expense, promptly compute such adjustment, and
      furnish Holder with a certificate of its Chief Financial Officer setting forth
      such adjustment and the facts upon which such adjustment is based. The Company
      shall, upon written request, furnish Holder a certificate setting forth the
      Warrant Price in effect upon the date thereof and the series of adjustments
      leading to such Warrant Price.




14




ARTICLE
      3. REPRESENTATIONS
      AND COVENANTS OF THE COMPANY .





3.1  Representations
      and Warranties .
      The
      Company represents and warrants to the Holder as follows: All Shares which
      may
      be issued upon the exercise of the purchase right represented by this Warrant,
      and all securities, if any, issuable upon conversion of the Shares, shall,
      upon
      issuance, be duly authorized, validly issued, fully paid and nonassessable,
      and
      free of any liens and encumbrances except for restrictions on transfer provided
      for herein or under applicable federal and state securities laws.





3.2  Notice
      of Certain Events .
      If the
      Company proposes at any time (a) to declare any dividend or distribution upon
      any of its stock, whether in cash, property, stock, or other securities and
      whether or not a regular cash dividend; (b) to offer for sale any shares of
      the
      Company's capital stock (or other securities convertible into such capital
      stock), other than (i) pursuant to the Company's stock option or other
      compensatory plans, (ii) in connection with commercial credit arrangements
      or
      equipment financings, or (iii) in connection with strategic transactions for
      purposes other than capital raising; (c) to effect any reclassification or
      recapitalization of any of its stock; (d) to merge or consolidate with or into
      any other corporation, or sell, lease, license, or convey all or substantially
      all of its assets, or to liquidate, dissolve or wind up; or (e) offer holders
      of
      registration rights the opportunity to participate in an underwritten public
      offering of the Company's securities for cash, then, in connection with each
      such event, the Company shall give Holder: (1) at least 10 days prior written
      notice of the date on which a record will be taken for such dividend,
      distribution, or subscription rights (and specifying the date on which the
      holders of common stock will be entitled thereto) or for determining rights
      to
      vote, if any, in respect of the matters referred to in (a) and (b) above; (2)
      in
      the case of the matters referred to in (c) and (d) above at least 10 days prior
      written notice of the date when the same will take place (and specifying the
      date on which the holders of common stock will be entitled to exchange their
      common stock for securities or other property deliverable upon the occurrence
      of
      such event); and (3) in the case of the matter referred to in (e) above, the
      same notice as is given to the holders of such registration rights.





3.3  Registration
      Under Securities Act of 1933, as amended .
      The
      Company represents and warrants that no shareholders or warrant holders of
      the
      Company have contractual rights to cause the Company to register their shares
      under the Securities Act of 1933, as amended, and accordingly no such rights
      are
      being granted to Holder with respect to the Shares.





3.4  No
      Shareholder Rights .
      Except
      as provided in this Warrant, the Holder will not have any rights as a
      shareholder of the Company until the exercise of this Warrant.





ARTICLE
      4. REPRESENTATIONS,
      WARRANTIES OF THE HOLDER .
      The
      Holder represents and warrants to the Company as follows:





4.1  Purchase
      for Own Account .
      This
      Warrant and the securities to be acquired upon exercise of this Warrant by
      the
      Holder will be acquired for investment for the Holder’s account, not as a
      nominee or agent, and not with a view to the public resale or distribution
      within the meaning of the Act. Holder also represents that the Holder has not
      been formed for the specific purpose of acquiring this Warrant or the
      Shares.




15




4.2  Disclosure
      of Information .
      The
      Holder has received or has had full access to all the information it considers
      necessary or appropriate to make an informed investment decision with respect
      to
      the acquisition of this Warrant and its underlying securities. The Holder
      further has had an opportunity to ask questions and receive answers from the
      Company regarding the terms and conditions of the offering of this Warrant
      and
      its underlying securities and to obtain additional information (to the extent
      the Company possessed such information or could acquire it without unreasonable
      effort or expense) necessary to verify any information furnished to the Holder
      or to which the Holder has access.





4.3  Investment
      Experience .
      The
      Holder understands that the purchase of this Warrant and its underlying
      securities involves substantial risk. The Holder has experience as an investor
      in securities of companies in the development stage and acknowledges that the
      Holder can bear the economic risk of such Holder’s investment in this Warrant
      and its underlying securities and has such knowledge and experience in financial
      or business matters that the Holder is capable of evaluating the merits and
      risks of its investment in this Warrant and its underlying securities and/or
      has
      a preexisting personal or business relationship with the Company and certain
      of
      its officers, directors or controlling persons of a nature and duration that
      enables the Holder to be aware of the character, business acumen and financial
      circumstances of such persons.





4.4 Accredited
      Investor Status .
      The
      Holder is an “accredited investor” within the meaning of Regulation D
      promulgated under the Act.





4.5  The
      Act .
      The
      Holder understands that this Warrant and the Shares issuable upon exercise
      or
      conversion hereof have not been registered under the Act in reliance upon a
      specific exemption therefrom, which exemption depends upon, among other things,
      the bona fide nature of the Holder’s investment intent as expressed herein. The
      Holder understands that this Warrant and the Shares issued upon any exercise
      or
      conversion hereof must be held indefinitely unless subsequently registered
      under
      the Act and qualified under applicable state securities laws, or unless
      exemption from such registration and qualification are otherwise available.





ARTICLE
      5. MISCELLANEOUS .





5.1  Term :
      This
      Warrant is exercisable in whole or in part at any time and from time to time
      on
      or before the Expiration Date.





5.2  Legends .  This
      Warrant and the Shares (and the securities issuable, directly or indirectly,
      upon conversion of the Shares, if any) shall be imprinted with a legend in
      substantially the following form:





THIS
      WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE
      SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR THE SECURITIES LAWS OF ANY
      STATE AND, EXCEPT AND PURSUANT TO THE PROVISIONS OF ARTICLE 5 BELOW, MAY NOT
      BE
      OFFERED, SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED UNLESS AND
      UNTIL
      REGISTERED UNDER SAID ACT AND APPLICABLE STATE SECURITIES LAW OR, IN THE OPINION
      OF LEGAL COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE ISSUER OF THESE
      SECURITIES, SUCH OFFER, SALE OR TRANSFER, PLEDGE OR HYPOTHECATION IS EXEMPT
      FROM
      REGISTRATION.




16




5.3  Compliance
      with Securities Laws on Transfer .
      This
      Warrant and the Shares issuable upon exercise of this Warrant (and the
      securities issuable, directly or indirectly, upon conversion of the Shares,
      if
      any) may not be transferred or assigned in whole or in part without compliance
      with applicable federal and state securities laws by the transferor and the
      transferee (including, without limitation, the delivery of investment
      representation letters and legal opinions reasonably satisfactory to the
      Company, as reasonably requested by the Company). The Company shall not require
      Holder to provide an opinion of counsel if the transfer is to Holder’s parent
      company, SVB Financial Group (formerly Silicon Valley Bancshares), or any other
      affiliate of Holder. Additionally, the Company shall also not require an opinion
      of counsel, so long as Rule 144 remains in effect in relevant part in
      substantially its current form, if (a) in the reasonable judgment of the
      Company, based in part upon reasonably detailed representations by the Holder
      or
      the selling broker, as appropriate, there is no material question as to the
      availability of current information as referenced in Rule 144(c), Holder has
      complied with Rule 144(d) and the selling broker has complied with Rule 144(f),
      and (b) the Company is provided with a copy of Holder's notice of proposed
      sale.





5.4  Transfer
      Procedure .
      Upon
      receipt by Holder of the executed Warrant, Holder may transfer all of this
      Warrant to Holder’s parent company, SVB Financial Group, by execution of an
      Assignment substantially in the form of Appendix 2. Subject to the provisions
      of
      Article 5.3 and upon providing Company with written notice, SVB Financial Group
      and any subsequent Holder may transfer all or part of this Warrant or the Shares
      issuable upon exercise of this Warrant (or the Shares issuable directly or
      indirectly, upon conversion of the Shares, if any) to any transferee, provided,
      however, in connection with any such transfer, SVB Financial Group or any
      subsequent Holder will give the Company notice of the portion of the Warrant
      being transferred with the name, address and taxpayer identification number
      of
      the transferee and Holder will surrender this Warrant to the Company for
      reissuance to the transferee(s) (and Holder if applicable). The Company may
      refuse to transfer this Warrant or the Shares to any person who directly
      competes with the Company, unless, in either case, the stock of the Company
      is
      publicly traded.





5.5  Notices .
      All
      notices and other communications from the Company to the Holder, or vice versa,
      shall be deemed delivered and effective when given personally or mailed by
      first-class registered or certified mail, postage prepaid, at such address
      as
      may have been furnished to the Company or the Holder, as the case may (or on
      the
      first business day after transmission by facsimile) be, in writing by the
      Company or such Holder from time to time. Effective upon receipt of the fully
      executed Warrant and the initial transfer described in Article 5.4 above, all
      notices to the Holder shall be addressed as follows until the Company receives
      notice of a change of address in connection with a transfer or
      otherwise:





SVB
      Financial Group


Attn:
      Treasury Department


3003
      Tasman Drive, HA 200


Santa
      Clara, CA 95054


Telephone:
      408-654-7400


Facsimile:
      408-496-2405




17


Notice
      to
      the Company shall be addressed as follows until the Holder receives notice
      of a
      change in address:







NORTH
      AMERICAN SCIENTIFIC, INC.


20200
      Sunburst Street


Chatsworth,
      California 91311


Telephone:
      (818) 734-8600


Facsimile:
      (818) 734-5223





5.6  Waiver .
      This
      Warrant and any term hereof may be changed, waived, discharged or terminated
      only by an instrument in writing signed by the party against which enforcement
      of such change, waiver, discharge or termination is sought.





5.7  Attorney’s
      Fees .
      In the
      event of any dispute between the parties concerning the terms and provisions
      of
      this Warrant, the party prevailing in such dispute shall be entitled to collect
      from the other party all costs incurred in such dispute, including reasonable
      attorney’s fees.





5.8  Automatic
      Conversion upon Expiration .
      In the
      event that, upon the Expiration Date, the fair market value of one Share (or
      other security issuable upon the exercise hereof) as determined in accordance
      with Section 1.3 above is greater than the Exercise Price in effect on such
      date, then this Warrant shall automatically be deemed on and as of such date
      to
      be converted pursuant to Section 1.2 above as to all Shares (or such other
      securities) for which it shall not previously have been exercised or converted,
      and the Company shall promptly deliver a certificate representing the Shares
      (or
      such other securities) issued upon such conversion to the Holder.





5.9  Counterparts .
      This
      Warrant may be executed in counterparts, all of which together shall constitute
      one and the same agreement.





5.10  Governing
      Law .
      This
      Warrant shall be governed by and construed in accordance with the laws of the
      State of Delaware, without giving effect to its principles regarding conflicts
      of law.








“COMPANY”
              
              **NORTH
                AMERICAN SCIENTIFIC, INC.**
              
              
              By:   
                /s/John
                B. Rush
              
              
              Name:John
                B. Rush
              
              (Print)
              Title:Chairman
                of the Board, President or
              Vice
                President
            By   
                /s/James
                W. Klingler
              
              
              Name:James
                W. Klingler
              
              (Print)
              Title:Chief
                Financial Officer, Secretary,
              Assistant
                Treasurer or Assistant Secretary




18




“HOLDER”
              
              **SILICON
                VALLEY BANK**
              
              
              By:/s/Derek
                Brunelle
              
              Name:Derek
                Brunelle
              
              (Print)
              Title:Vice
                President




19


**APPENDIX
      1**




**NOTICE
      OF EXERCISE**





1.  Holder
      elects to purchase ___________ shares of the Common/Series _____ Preferred
      [strike one] Stock of __________________ pursuant to the terms of the attached
      Warrant, and tenders payment of the purchase price of the shares in
      full.




[or]




1.  Holder
      elects to convert the attached Warrant into Shares/cash [strike one] in the
      manner specified in the Warrant. This conversion is exercised for
      _____________________ of the Shares covered by the Warrant.




[Strike
      paragraph that does not apply.]




2.  Please
      issue a certificate or certificates representing the shares in the name
      specified below:





___________________________________________


Holders
      Name








___________________________________________





___________________________________________


(Address)





3.  By
      its
      execution below and for the benefit of the Company, Holder hereby restates
      each
      of the representations and warranties in Article 4 of the Warrant as the date
      hereof.







HOLDER:





_________________________








By:__________________________





Name:________________________





Title:_________________________





(Date):_______________________





20


**APPENDIX
      2**




**ASSIGNMENT**





For
      value
      received, Silicon Valley Bank hereby sells, assigns and transfers
      unto




Name: SVB
      Financial Group




Address: 3003
      Tasman Drive (HA-200)


Santa Clara, CA 95054




Tax
      ID: 91-1962278




that
      certain Warrant to Purchase Stock issued by North American Scientific, Inc.
      (the
“Company”), on August 24, 2007 (the “Warrant”) together with all rights, title
      and interest therein.




SILICON
              VALLEY
              BANKDate: August
              24, 2007
            By:
            /s/Derek
              BrunelleName:Derek
              BrunelleTitle:Vice
              President









By
      its
      execution below, and for the benefit of the Company, SVB Financial Group makes
      each of the representations and warranties set forth in Article 4 of the Warrant
      and agrees to all other provisions of the Warrant as of the date
      hereof.




SVB
              FINANCIAL
              GROUPBy:
            /s/ Paulette
              M. MeansName:  
Paulette
              M. MeansTitle:
                Treasurer




21