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                                                                   Exhibit 10.20

[Logo of National Research Council of Canada]

                                                     Date drafted: 27 March 2000
                                                              Case Number: 11104

GIVEN BY NATIONAL RESEARCH COUNCIL OF CANADA                  (called "NRC")
      Head     {1200 Montreal Road,        Participating  Institute for National
      Office   {Ottawa, Ontario KIA OR6    Institute      Measurement Standards

TO       NOMOS Corporation (called the "User")
         whose address is:
                  2591 Wexford Bayne Road
                  Sewickley, PA 15143
                  U.S.A.


PREAMBLE

The User desires to use computer software created by NRC and identified as BEAM
99 (called herein the "Software").

IN CONSIDERATION of the preamble and the terms below, the Parties agree as
follows:

SL-1     TITLE AND GRANT

         NRC grants to the User, and User accepts, a non-transferable,
         non-exclusive licence to use the Software only in the manner described
         under the heading "USAGE". All proprietary interest, right, title, and
         copyright in the Software remain with NRC.

SL-2     TERM

         This Licence is in effect until 31 December, 2000 ("Initial Term").
         Thereafter, the User will have the right to continue this licence for
         one year periods upon payment of the annual licence fee, which is due
         on the expiration of the Initial Term and each anniversary thereof.

SL-3     PAYMENTS BY THE USER

         The User must pay an initial licence fee of Thirty thousand U.S.
         Dollars ($ 30,000.00) upon execution of this agreement. Thereafter, to
         continue this licence, the User must pay an annual licence fee of
         Thirty thousand United States Dollars ($30,000.00) as set out in SL-2.
         Neither the initial licence fee or the annual licence fees are
         refundable.

         Invoices will not be sent. The User must remit payment with the
         executed agreement. Cheques are to be made out to "Receiver General -
         National Research Council". Customs duties, if applicable, will be paid
         by the User.






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Cheques must be addressed to:

         Finance and Information Management Services
         National Research Council
         1200 Montreal Road, Ottawa, Ontario, KIA OR6

The case number 11104 should be noted on the check.

SL-4     USAGE

         4.1      The User may install the software on an unlimited number of
                  workstations located solely at the Users address at 2591
                  Wexford Bayne Road, Sewickley, PA 15143, U.S.A.. NRC agrees
                  that the software may also be installed on the workstations of
                  the Users contractor, Lawrence Livermore National Laboratory
                  (LLNL) located solely at 7000 East Avenue, Livermore CA
                  945550, USA provided that LLNL certifies in writing that it
                  agrees to be bound by the terms and conditions of this
                  licence. (letter attached)

         4.2      Subject to clause 4.3, the User may not lease, sublicense,
                  sell or transfer the Software or create and lease, sublicense,
                  sell or transfer any derivative programs that incorporate,
                  embody or are derived in any way from the Software.

         4.3      The User may only use the software for internal work to
                  develop beam characterization models for generic accelerators
                  which it may incorporate into its Peregfine related treatment
                  planning software and provide to third parties. The User
                  agrees not to use the Software to provide services or data to
                  third parties which are in any way based on modelling any
                  third party's individual accelerator.

         4.4      The Software constitutes valuable trade secrets which are
                  provided to the User for the sole internal use of the User and
                  which must not be made available to any other person.

         4.5      NRC agrees to provide, when available, any corrections, bug
                  fixes and updates of the Software to the User under this
                  licence. However, access to a new version of the Software (for
                  example BEAMOO) is not included and shall be the subject of a
                  separate licence.

         4.6      This licence does not include the fight to use the EGS4
                  Software and the User is responsible for independently
                  obtaining all necessary authorizations for such use.




                                      -2-
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SL-5.    TERMINATION PROCEDURE

         5.1      The User may terminate this licence at any time, by notifying
                  NRC in writing. NRC may terminate this licence by notifying
                  the User if the User violates any term of this Agreement and
                  the violation is not corrected to the satisfaction of NRC
                  within thirty (30) days after NRC gives the User notice in
                  writing of the allegation of a violation.

         5.2      Immediately upon notice of termination by either the User or
                  NRC, the User must certify that no copies, portions, modified
                  versions, or translations of the Software remain accessible to
                  the User, and that none have been passed from the User to
                  third parties.

         5.3      Termination by either the User or NRC does not erase any debt
                  already due pursuant to this Agreement.

SL-6     LIMITED WARRANTY AND REMEDIES

         6.1      NRC makes no warranty with respect to the accuracy of the
                  software code. NRC will use its best efforts to attempt to
                  correct any minor defects reported by the User to NRC. NRC
                  will not provide any technical assistance or support under
                  this licence but, at its discretion, will respond to minor
                  requests from the User. The provision of any other support or
                  technical services will be the subject of a separate agreement
                  between the parties.

         6.2      NRC warrants that the Software does not infringe any copyright
                  or violate any obligation of confidentiality. NRG also
                  warrants that NRC is not actually aware of any patent which
                  may be infringed by the Software. If a breach of a warranty
                  mentioned in this paragraph is proved in a court, NRC will
                  cancel all debts owing and refund all payments made pursuant
                  to this Agreement within the three (3) years preceding the
                  commencement of the court action.

         6.3      EXCEPT AS EXPRESSLY STATED HEREIN, NRG DISCLAIMS ANY
                  WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, OF ANY KIND OR
                  NATURE WITH RESPECT TO THE SOFTWARE, INCLUDING WITHOUT
                  LIMITATION ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A
                  PARTICULAR PURPOSE. NRC SHALL NOT BE LIABLE IN ANY EVENT FOR
                  ANY DAMAGES, WHETHER DIRECT OR INDIRECT, SPECIAL OR GENERAL,
                  CONSEQUENTIAL OR INCIDENTAL, ARISING FROM THE USE OF THE
                  SOFTWARE.





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SL-7     GENERAL

         7.1      This Agreement supersedes all prior communications,
                  negotiations and agreements, written or oral, concerning the
                  Software. No amendment or waiver of terms is effective unless
                  it is in writing, signed by both Parties, and specifically
                  states the intention to affect this Agreement.

SIGNED by the User in duplicate at .....Sewickley, PA..........................

NOMOS CORPORATION

                                    Date:            3-28-00
                                            -----------------------------------


                                            John W. Manzetti
                                            Executive Vice President and
                                            Chief Financail Officer
                                            NOMOS Corporation
                                    per:                   /s/ John W. Manzetti
                                            -----------------------------------
                                            Print name and title


SIGNED by NRC in duplicate at Ottawa, Ontario, Canada:

NATIONAL RESEARCH COUNCIL OF CANADA



                                    Date:
                                            -----------------------------------



                                    per:
                                            -----------------------------------
                                            Print name and title




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Letter to be signed by NOMOS and LLNL. Copy to be returned to NRC with the
executed agreement.


Date:



Mr. Ralph Patterson
Lawrence Livermore National Laboratory
7000 East Avenue, L-051
Livermore, California  94550

Dear Mr. Patterson:

As our contractor for the PEREGRINE project under the terms of Work for others
Agreement L-8788, NOMOS is furnishing you a copy of BEAM99 for use in performing
the required tasks of this agreement. BEAM99 is owned by the National Research
Council of Canada, and licensed by NOMOS for the purposes of developing beam
characterization models for generic accelerators. The license specifically
excludes providing services or data to third parties which are in any way based
on modeling any third party's individual accelerator.

By cosigning this letter, Lawrence Livermore National Laboratory agrees to use
this software solely in accordance with the terms of the National Research
Council licence in performing agreement L-8788, and that it will return the
software when requested by NOMOS.

Signed,



Robert M. Oates, Vice President Engineering
NOMOS Corporation


Agreed,




Ralph W. Patterson, Product Manager
Lawrence Livermore National Laboratory