Exhibit
      10.1

    


    April
      23, 2007

    


    


     

    Michael
      Ryan

    c/o
      NOMOS Corporation

    200
      West Kensinger Drive, Suite 100

    Cranberry
      Township 16066 

    


    


    Dear
      Mike: 

     

    This
      letter shall serve as an amendment to the letter agreement (the “Amendment”)
      between yourself and North American Scientific, Inc. (“the Company”), dated
      January 10, 2006. 

    


    Salary
      Increase and Severance Benefits

    


    The
      Compensation Committee of the Board of Directors of the Company has authorized
      a
      salary increase, effective May 1, 2007, to $218,748 annually. In addition,
      in
      the event your employment is terminated by the Company without Cause (as that
      term is defined below), you will be entitled to receive nine (9) months of
      severance pay (based upon the annual rate of base salary in effect for you
      immediately prior to your termination) in lump sum or in salary continuation,
      at
      the option of the Company. If this nine (9) month severance pay is triggered
      pursuant to this Amendment, you will also receive nine (9) month benefit
      continuation to the extent allowed by law. 

    


    For
      the purposes of this Amendment, termination with cause shall be understood
      to
      mean the Company’s termination of your employment for any of the following
      reasons: (i) your commission of any act of fraud, embezzlement or dishonesty,
      (ii) your unauthorized use or disclosure of any confidential information or
      trade secrets of the Company, (iii) any intentional misconduct by you which
      has
      a materially adverse effect upon the Company’s business or reputation, (iv) your
      continued failure to perform the major duties, functions and responsibilities
      of
      your position after written notice from the Company identifying the deficiencies
      in your performance and a reasonable cure period of not less than thirty (30)
      days or (v) a material breach of your fiduciary duties as an officer of the
      Company. 

    


    Should
      your employment cease by reason of a termination with cause or should you
      voluntarily resign, then the Company will only be required to pay you (i) any
      unpaid compensation earned for services previously rendered through the date
      of
      such termination and (ii) any accrued but unpaid vacation benefits or sick
      days.

     

    Retention
      Bonus

    


    In
      addition to the benefits listed above, the Company will pay you, in lump sum,
      a
      bonus equal to three (3) months of your base salary for retaining your
      employment with the Company until such time as the Company’s NOMOS Corporation
      subsidiary (“NOMOS”) has been: 

    


    
      
         

      

      
         

        
          

        

      

      
         

      

    

    	·  	
            merged
              or consolidated in a transaction where all or substantially all of
              NOMOS’
              assets have been sold or transferred, or, alternatively, where more
              than
              fifty percent (50%) of the total combined voting power of NOMOS securities
              are transferred to a person or persons different from the persons holding
              those securities immediately prior to such transaction;
              

          


    


    	·  	
            dissolved,
              shutdown or otherwise placed into bankruptcy proceedings (or substantially
              similar); or, 

          


    


    	·  	
            substantially
              restructured to an extent which is acceptable to the Company’s Board of
              Directors. 

          


    


    The
      Company and you shall agree in writing, no later than June 1, 2007, upon a
      date
      by which this retention bonus shall be paid. In no event shall this retention
      bonus be paid later than October 31, 2007. 

    


    Guaranteed
      Bonus for Fiscal 2007

    


    Finally,
      for fiscal 2007 only, you will receive a minimum of 50% of your available annual
      bonus (currently a 25% target bonus of your annual base salary) (the “Guaranteed
      Bonus”). In the event your employment terminates for any reason prior to October
      31, 2007, you will receive your Guaranteed Bonus, pro-rated to reflect your
      length of service during fiscal 2007. Nothing in this Amendment shall be
      understood to prevent you from receiving an annual bonus which exceeds the
      amount of the Guaranteed Bonus, in the event that the Compensation Committee
      determines that achievement of personal and corporate goals warrants such an
      award. 

    


    Miscellaneous

    


    All
      other terms and conditions of your letter agreement dated January 10, 2006
      shall
      remain in full force and effect, including, without limitation, the fact that
      your employment with the Company remains at-will. This Amendment may only be
      amended by written instrument signed by you and an authorized officer of the
      Company. With respect to the subject matter hereto, this Amendment supersedes
      and replaces all previous severance or change in control contracts and
      agreements, and, along with the letter agreement dated January 10, 2006
      constitutes the entire agreement between you and the Company. No oral statements
      or prior written material, unless specifically incorporated herein, shall be
      of
      any force and effect. 

    


    


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    Please
      indicate your agreement with the foregoing terms and conditions of your change
      in control severance package by signing the Acceptance section of the enclosed
      copy of this letter and returning it to the Company. 

     

    
      	 	Very truly
              yours,	 	 	 
	 	 	 	 	 	 
	 	NORTH
              AMERICAN SCIENTIFIC, INC.	 	 	 
	 	 	 	 	 	 
	 	 	 	 	 	 
	 	By:	/s/ John
              B.
              Rush	 	 	 
	 	 	
              
John
              B. Rush	 	 	
            
	 	 	 	 	 	 
	 	Title:	President
              and
              Chief Executive Officer	 	 	 
	 	 	
              

            	 	 	 
	 	 	 	 	 	 
	ACCEPTANCE	 	 	 
	 	 	 	 	 	 
	 	I hereby
              agree to all
              the terms and provisions of the foregoing Amendment.	 
	 	 	 	 	 	 
	 	 	 	 	 	 
	 	Signature:	/s/ Michael C. Ryan	 	 	 
	 	 	
              
 	 	 	 
	 	Dated:	04-24-07