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                                                                 Exhibit 10.9(b)



                          AMENDMENT TO LEASE AGREEMENT
                SPECTRA OFFICE BUILDING II - EXPANSION ON LEVEL I


         THIS AMENDMENT to Lease Agreement is made the 10th day of April 1995,
by and between Spectra Development Company, (the "Lessor")

                                      A N D

         The NOMOS Corporation, (the "Lessee").

                                    RECITAL
                                    -------

Lessee has leased 17,489 square feet of Rentable Area in the Spectra Office
Building II under a Lease Agreement dated August 18, 1994 (the "Lease
Agreement").

NOW THEREFORE, intending to be legally bound hereby, and for good and valuable
consideration, the parties agree to amend the Lease Agreement as follows:

1) The Recital set forth above are incorporated herein and made a part hereof.

2) During the Effective Term of this Amendment to Lease Agreement ("Amendment"),
the Lease Agreement shall be amended as follows:

         a) Section 1.01 of the Lease Agreement is hereby amended to include
that certain 839 square feet of rentable area, as defined in Exhibit "I",
attached hereto and made a part hereto.

         b) Section 1.02 of the Lease Agreement is hereby amended to provide
that Rentable Area is increased by 839 rentable square feet for the term of this
Amendment.

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         c) Section 2.01(j) of the Lease Agreement is hereby amended to provide
that the Lessee's Percentage of Operating Expense is increased by 2.64% for the
term of this Amendment.

         d) Section 2.01(k) of the Lease Agreement is to provide that Lessee's
Percentage of Taxes is increased by 2.64% for the term of this Amendment.

         e) Section 4.01 of the Lease Agreement is hereby amended to provide
that the monthly rental is increased by $1,258.50 for the term of this
Amendment.

3) The effective Term of this Amendment shall be as follows:

         a) The Effective Term shall commence on MARCH 1, 1996 and terminate 60
months from this commencement date of this Amendment.

4) Section 5.01 of the Lease Agreement is hereby amended to provide that the
Lessee shall pay 57.75% of the excess of Taxes and 2.64% of the excess of
Operating Expense from the Base Year as Additional Rent.

5) Section 9.01 shall be amended to provide that all Rent shall be payable to
the Lessor or its agents at the address of Spectra Development Company at 2591
Wexford Bayne Road, Sewickley, PA 15143.

6) Lessee agrees to the build out improvements and cost of construction as
defined in Exhibit "II" attached and hereby made a part hereof.

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7) Upon termination of the Effective term hereof, all of the terms and
conditions of this Amendment shall be null and void and the terms and conditions
of the Lease Agreement (as amended by other instruments, if any) shall be in
full force and effect.

8) Lessor and Lessee do hereby ratify all other terms and conditions set forth
in the Lease Agreement which are not affected hereby and do hereby acknowledge,
agree, and affirm that all of the other terms and conditions of the Lease
Agreement are in full force and effect, except as specifically modified hereby.

         IN WITNESS WHEREOF, the parties have set their hands and seals the day
and year first above written.

WITNESS:                                SPECTRA DEVELOPMENT CO.


/s/ Susan A. Majeski                    By: /s/ Gary A. Sippel
---------------------------------          -------------------------------------
                                           Gary A. Sippel




WITNESS:                                NOMOS CORPORATION


/s/ [Illegible]                         By: /s/ R. L. Graham
---------------------------------          -------------------------------------



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                                   EXHIBIT "I"
                                  [FLOOR PLAN]