Document:

<PAGE>
                                                                 Exhibit 10.3(b)

                                NOMOS CORPORATION
                             2591 WEXFORD BAYNE ROAD
                               SEWICKLEY, PA 15143

Cross-Atlantic Partners
Cross-Atlantic Partners II
Cross-Atlantic Partners III
650 Madison Avenue
New York, New York 10022
Attn:  John Cassis, Partner

         Re:   Amendment to Letter Agreement dated September 28, 1999
               ------------------------------------------------------

Dear John:

         Reference is made to the letter agreement (the "LETTER AGREEMENT")
dated September 28, 1999 between NOMOS Corporation (the "COMPANY"), each of
Cross-Atlantic Partners, Cross-Atlantic Partners II and Cross-Atlantic Partners
III (collectively, "CROSS-ATLANTIC"), and John A. Friede, individually, with
respect to Sections 1.2 and 1.3 thereof. We would like to amend the Letter
Agreement to clarify that it will terminate it its entirety upon an initial
public offering by the Company of its common stock.

         Therefore, the undersigned, intending to be legally bound, agree as
follows:

         A. TERMINATION UPON QUALIFIED INITIAL PUBLIC OFFERING. The Letter
Agreement shall terminate and shall be of no further force and effect upon the
consummation of a Qualified Public Offering. For purposes of the foregoing, the
term "QUALIFIED PUBLIC OFFERING," means an initial public offering by the
Company of its common stock that results in net proceeds to the Company of at
least $15 million.

         B. OTHER PROVISIONS TO REMAIN IN EFFECT. Except as specifically amended
pursuant to the foregoing Section A, the Letter Agreement shall remain in full
force and effect in accordance with its prior terms.

         If the foregoing accurately sets forth the agreements that the Company
and Cross-Atlantic have reached with respect to the subject matter hereof,
please indicate your agreement to the terms contained herein by countersigning
in the place indicated below.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

<PAGE>

                                  Sincerely,

                                  NOMOS CORPORATION

                                  By:  /s/ John W. Manzetti
                                     ------------------------------------------
                                         John W. Manzetti,
                                         President and Chief Executive Officer

AGREED AND ACCEPTED:

CROSS-ATLANTIC PARTNERS
CROSS-ATLANTIC PARTNERS II
CROSS-ATLANTIC PARTNERS III

By:  /s/ John Cassis
   ---------------------------------

Name:  CASSIS
      ------------------------------

Title:  Partner
       -----------------------------

Date:    4/26/02
     -------------------------------CONFIDENTIAL TREATMENT REQUESTED: CONFIDENTIAL PORTIONS OF THIS DOCUMENT
     HAVE BEEN REDACTED AND HAVE BEEN FILED SEPARATELY WITH THE COMMISSION.

INTEROFFICE MEMO

TO:               Will Wells

FROM:             John Manzetti

Subject:          2002 Incentive Compensation

Date:             February 22, 2002

CC:               Jill Welch, David Haffner

Dear Will,

This letter reconfirms the components of your incentive compensation for 2002,
and outlines the Company Financial Performance component as approved by the
NOMOS Corporation Compensation Committee on February 11, 2002.

For 2002, your incentive compensation plan opportunity will be as follows:

         Personal and Department Objectives:
                  $150,000 bonus opportunity may be earned based on your
                  achievement of personal and department objectives.

         Company Financial Performance:
                  $50,000 bonus opportunity may be earned based on Company
                  Pre-Tax Income thresholds as follows:

                  Pre-Tax           % Bonus
                  INCOME(1)         EARNED (cumulative)
                  ---------         ------
                  $[* * *]          25%
                  $[* * *]          50%
                  $[* * *]          75%
                  $[* * *]          90%
                  $[* * *]          100%

                  (1) Pre-Tax Income is net of the bonuses accrued.

The above is in addition to any bonus you may earn under the 2002 NOMOS
Corporation Profit Sharing Plan.

Any bonus amount earned must be approved by the NOMOS Corporation Compensation
Committee will be paid after the financial closing of fiscal year 2002 on or
about March 15, 2003.

Best regards,

/s/ John

John [Manzetti]

-------------
* * * Confidential material redacted and filed separately with the Commission.

<PAGE>

Confidential Treatment

                            [NOMOS Corporation Logo]

June 21, 1999

PERSONAL AND CONFIDENTIAL

Mr. William W. Wells
7425 Craigleith Drive
Duluth, GA 30097

Dear Will:

On behalf of NOMOS Corporation, I am delighted to extend the following offer of
employment to you. The terms of the offer are presented below:

1.   TITLE: Vice President - Sales and Marketing of the NOMOS Corporation. In
     this capacity, you will report to Anil Rastogi, Ph.D., CEO and President of
     NOMOS Corporation. Your responsibilities will include the worldwide Sales
     and Marketing functions of NOMOS Corporation as well as managing the
     Technical Support organization.

2.   COMPENSATION:

     a.   SALARY: Your initial salary will be $175,000 per annum payable in
          accordance with normal company guidelines.

     b.   INCENTIVE: Your incentive will be $125,000 per annum. For each of your
          first two years of employment, $50,000 of the incentive will be
          guaranteed, and $75,000 will be based on mutually agreed upon sales
          and profit goals. Beyond your first two years of employment, this
          incentive will be entirely based on the achievement of mutually agreed
          upon sales and profit goals. At the end of each 12-month period, you
          will receive a salary and incentive opportunity review based upon your
          performance.

     c.   STOCK OPTIONS: You will be granted 100,000 shares of incentive stock
          options at an option price of $10.00 per share. These options will
          vest in four equal installments over four years. Where required by
          federal regulation, these stock options may be granted as
          non-qualified stock options.

3.   SIGN ON BONUS: You will receive a sign-on bonus of $50,000, payable within
     10 days of your start date.

<PAGE>

Confidential Treatment

4.   SEVERANCE AGREEMENT: In the event of termination without cause, NOMOS
     agrees to continue to pay you your base salary for the longer of
       (a) THE BALANCE OF THE TWO YEAR PERIOD ENDING, MAY 31, 2001, OR
       (b) 12 MONTHS.
     The minimum 12-month severance arrangement for termination other than for
     cause shall continue during the term of your employment.

5.   EXPENSES: You will be reimbursed for reasonable travel and business
     expenses as well as reasonable expenses associated with setting up an
     office in your home including fax and other office equipment.

6.   BENEFITS: You will receive standard company benefits, which will include
     four weeks vacation. Also included is UI medical, dental and disability
     insurance.

Additionally, enclosed is a confidentiality agreement for your review and
acceptance. Please sign and return that agreement with this letter.

We are looking forward to your joining NOMOS on Monday, June 28, 1999. We know
you will make many contributions to NOMOS as a member of the senior leadership
team.

Best regards,

/s/ John W. Manzetti

John W. Manzetti
Executive Vice President and CFO
NOMOS Corporation

                                        Agreed and accepted by:

                                       /s/ William W. Wells             7/14/99
                                       -----------------------------------------
                                       William W. Wells                   Date

cc:  Cynthia A. Stokvis<PAGE>

                                                                EXHIBIT 10.19(c)

CONFIDENTIAL TREATMENT REQUESTED: CONFIDENTIAL PORTIONS OF THIS DOCUMENT HAVE
BEEN REDACTED AND HAVE BEEN FILED SEPARATELY WITH THE COMMISSION.

                                 AMENDMENT TWO
                                       TO
                               LIMITED EXCLUSIVE
                             PATENT, COPYRIGHT AND
                          TRADEMARK LICENSE AGREEMENT

                                      FOR

                     PEREGRINE(TM) DOSE CALCULATION SYSTEM

                        FOR RADIATION TREATMENT PLANNING

                                    BETWEEN

                  THE REGENTS OF THE UNIVERSITY OF CALIFORNIA

                                      AND

                               NOMOS CORPORATION

                            LLNL CASE NO. TL-1613-99

                     LAWRENCE LIVERMORE NATIONAL LABORATORY
                            UNIVERSITY OF CALIFORNIA
                    P.O. BOX 808, L-795, LIVERMORE, CA 94551
                 INDUSTRIAL PARTNERSHIPS AND COMMERCIALIZATION

                                   JUNE 2002
<PAGE>

CONFIDENTIAL TREATMENT

                                 AMENDMENT TWO

NOMOS Corporation                                   Radiation Treatment Planning
                                                                   Amendment Two
--------------------------------------------------------------------------------

                                 AMENDMENT TWO
                                   June 2002

                                       to

                License Agreement - LLNL Case Number TL-1613-99
                   For PEREGRINE(TM) DOSE CALCULATION SYSTEM
                        For Radiation Treatment Planning
                         between NOMOS Corporation and
                  The Regents of the University of California
                            effective July 20, 1999

This Amendment Two to the License Agreement by and between The Regents of the
University of California ("THE REGENTS") and NOMOS Corporation ("LICENSEE")
will be effective as of the date of execution of this Amendment by both
Parties. This Amendment and the associated License Agreement are subject to
overriding obligations to the Federal Government pursuant to the provisions of
THE REGENTS' Contract No. W-7405-ENG-48 with the United States Department of
Energy ("DOE") for the operation of the Lawrence Livermore National Laboratory
("LLNL").

This Amendment Two will modify the field of use, some performance obligations,
and royalty fees as reflected in the amended Exhibits B (RIGHTS GRANTED AND
PERFORMANCE OBLIGATIONS) and C (FEES AND ROYALTIES). All other terms and
conditions remain the same.

Therefore, in consideration of the mutual covenants and obligations recited
herein, THE REGENTS and LICENSEE hereby amend the License Agreement as follows:

1.  EXHIBIT B (RIGHTS GRANTED AND PERFORMANCE OBLIGATIONS) AND EXHIBIT C (FEES
    AND ROYALTIES) are replaced in their entirety as follows:

--------------------------------------------------------------------------------

                                       1
<PAGE>

CONFIDENTIAL TREATMENT

                                 AMENDMENT TWO

NOMOS Corporation                                   Radiation Treatment Planning
                                                                   Amendment Two
--------------------------------------------------------------------------------

             EXHIBIT B - RIGHTS GRANTED AND PERFORMANCE OBLIGATIONS

                                     NOTICE
                                     ------

      LICENSEE CONSIDERS INFORMATION IN THIS EXHIBIT B TO BE PROPRIETARY.

B.1   RIGHTS GRANTED

      B.1.1  Rights to Licensed Patents

             Subject to the limitations set forth in this Agreement, THE REGENTS
             hereby grants to LICENSEE an exclusive, nontransferable,
             royalty-bearing license to: 1) make, have made, use, sell, offer
             for sale, and import Licensed Products in the Field of Use, and b)
             practice Licensed Methods in the Field of Use.

      B.1.2  Rights to Licensed Copyrights

             Subject to the terms and conditions of this Agreement, THE REGENTS
             grants to LICENSEE an exclusive, nontransferable, royalty-bearing
             license to duplicate, display, perform, make Derivative Works,
             distribute and have distributed, and sell Licensed Products covered
             by Licensed Copyrights in the Field of Use.

      B.1.3  Rights to Licensed Trademarks

             Subject to the terms and conditions of this Agreement, THE REGENTS
             hereby grants LICENSEE an exclusive license to use Licensed
             Trademarks, in corresponding Territories, as specified in Exhibit E
             (LICENSED TRADEMARKS), on Licensed Products or for Licensed Methods
             in the Field of Use.

--------------------------------------------------------------------------------

                                       2

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CONFIDENTIAL TREATMENT

                                 AMENDMENT TWO
NOMOS Corporation                                   Radiation Treatment Planning
                                                                   Amendment Two
--------------------------------------------------------------------------------

          B.1.4     "Field of Use" means planning human and animal cancer
                    therapies based on tumor radiation with photons or electrons
                    that are generated either by a radiation source external to
                    the patient (teletherapy) or an encapsulated radiation
                    source internal to the patient (brachytherapy).

B.2       SUBLICENSING RIGHTS

          THE REGENTS also grants to LICENSEE the right to issue royalty-bearing
          sublicenses to third parties in the Field of Use, having rights no
          greater than those granted to LICENSEE, provided that LICENSEE has
          exclusive rights in such Licensed Patents, Licensed Copyrights, and
          Licensed Trademarks in the Field of Use at the time of sublicensing.
          LICENSEE may issue sublicenses to Licensed Trademarks only in
          conjunction with LICENSEE's sublicensing of Licensed Patents and
          Licensed Copyrights.

          A Use Sublicense is considered to be a Licensed Product and not a
          sublicense as contemplated in this B.2.

B.3       RIGHTS EXCLUDED

          Rights that are not specifically granted in this Exhibit B or
          elsewhere in this Agreement are specifically excluded from the
          license. In particular, no license, express or implied, is granted to
          LICENSEE to Licensed Trademarks outside the corresponding Territory as
          specified in Exhibit E (LICENSED TRADEMARKS).

B.4       FUTURE RIGHTS

          Licensable WFO Subject Inventions and Licensable WFO Computer Software
          will be added to Exhibit A by amendment.

--------------------------------------------------------------------------------
                                       3
<PAGE>

CONFIDENTIAL TREATMENT

                                 AMENDMENT TWO
NOMOS Corporation                                   Radiation Treatment Planning
                                                                   Amendment Two
--------------------------------------------------------------------------------

B.5      PERFORMANCE OBLIGATIONS

         B.5.1 LICENSEE will proceed diligently to develop, file relevant
               regulatory applications for and attempt to obtain relevant
               regulatory commercialization approvals with respect to the
               manufacturing, marketing, and sale of Licensed Products for all
               uses in the Field of Use.  LICENSEE will file with the U.S. Food
               and Drug Administration at least one 510k Application or PMA
               (Pre-Market Approval) for clearance of Licensed Products for at
               least teletherapy uses within one (1) year of the Effective Date.

               Notwithstanding any other term of this Agreement, for the
               purposes of (a) invoking/complying with the Hatch-Waxman Act (35
               U.S.C. Section 156) and any corresponding rules and regulations
               of the U.S. Patent & Trademark Office regarding patent term
               extension, and (b) seeking regulatory approval of LICENSEE's
               Licensed Products and Licensed Methods, LICENSEE shall act as THE
               REGENTS' agent. To the extend deemed necessary by LICENSEE, in
               good faith, the Parties will cooperate to secure regulatory
               approval of LICENSEE's Licensed Products and Licensed Methods.

         B.5.2 LICENSEE will release for distribution and offer Sales of
               Licensed Products by the later date of either October 1, 2000, or
               within sixty (60) days after the date of FDA clearance for
               teletherapy uses of Licensed Products.

         B.5.3 LICENSEE will have gross revenues from Sales of Licensed Products
               or use of Licensed Methods of at least [***] per calendar year,
               as measured at the close of LICENSEE'S business on December 31 of
               the relevant calendar year, commencing with the later of

---------------
***Confidential material redacted and filed separately with the Commission.

--------------------------------------------------------------------------------

                                       4
<PAGE>

CONFIDENTIAL TREATMENT

                                 AMENDMENT TWO
                                                    Radiation Treatment Planning
NOMOS Corporation                                                  Amendment Two
--------------------------------------------------------------------------------

              calendar year 2004, or the first full calendar year after a
              Licensed Product has been released for distribution and offered
              for sale in accordance with paragraph B.5.2.

     B.5.4    LICENSEE will release for distribution and offer first OEM sale of
              Licensed Products that interface with radiation treatment planning
              systems that are manufactured and sold, or otherwise distributed
              to third parties, by entities other than LICENSEE by the later
              date of either October 1, 2001, or one year after initial release
              for distribution and offer of Sales of Licensed Products as
              defined in B.5.2. To the extent that some commercial entities may
              prefer to sublicense Licensed Patents and Licensed Copyrights
              rather than to purchase Licensed Products on an OEM basis,
              LICENSEE's sublicenses may satisfy this OEM performance
              obligation.

     B.5.5    LICENSEE will release for distribution and offer first sale of
              Licensed Products in the Field of Use for brachytherapy by the
              later date of either [***], or within sixty (60) days after the
              date of FDA clearance for brachytherapy uses of Licensed Products.

     B.5.6    LICENSEE will release for distribution and offer first sale of
              Licensed Products in the Field of Use for inverse treatment
              planning by the later date of either [***], or within sixty (60)
              days after the date of FDA clearance for inverse treatment
              planning uses of Licensed Products.

     B.5.7    LICENSEE will release for distribution and offer first sale of
              Licensed Products in the Field of Use for electron radiotherapy by
              the later date of either [***], or within sixty (60) days after
              the date of FDA clearance for electron radiotherapy uses of
              Licensed Products.

---------------
***Confidential material redacted and filed separately with the Commission.

--------------------------------------------------------------------------------

                                       5
<PAGE>

CONFIDENTIAL TREATMENT

                                 AMENDMENT TWO
                                                    Radiation Treatment Planning
NOMOS Corporation                                                  Amendment Two
--------------------------------------------------------------------------------

     B.5.8    The sales and other performance requirements specified above may,
              by mutual written consent of LICENSEE and THE REGENTS, be amended
              and/or extended at the written request of LICENSEE to THE REGENTS,
              based upon legitimate business or technical reasons specified in
              reasonable detail in such written request. THE REGENTS will not
              unreasonably withhold its consent to requests made in accordance
              with this paragraph.

     B.5.9    The first progress report will be due on February 28, 2000.

--------------------------------------------------------------------------------

                                       6
<PAGE>

CONFIDENTIAL TREATMENT

                                 AMENDMENT TWO

NOMOS Corporation                                   Radiation Treatment Planning
                                                                   Amendment Two
--------------------------------------------------------------------------------
                         EXHIBIT C - FEES AND ROYALTIES

                                     NOTICE
                                     ------

       LICENSEE CONSIDERS INFORMATION IN THIS EXHIBIT C TO BE PROPRIETARY.

C.1    LICENSE ISSUE FEE

       C.1.1  As partial consideration for this Agreement, LICENSEE will pay to
              THE REGENTS a nonrefundable issue fee of [***] (License Issue Fee)
              as follows:

              C.1.1.1 [***] to be paid when LICENSEE executes the Agreement.

              C.1.1.2 [***] to be paid no later than October 1, 1999.

              C.1.1.3 [***] to be paid no later than November 1, 1999.

              C.1.1.4 [***] to be paid no later than December 1, 1999.

              C.1.1.5 [***] to be paid no later than January 1, 2000.

              C.1.1.6 [***] to be paid no later than February 1, 2000.

       C.1.2  THE REGENTS will execute the Agreement after receipt of LICENSEE's
              executed copies of the Agreement and payment of the first
              installment of the License Issue Fee specified in C.1.1.1 above.

---------------
***Confidential material redacted and filed separately with the Commission.

--------------------------------------------------------------------------------

                                       7
<PAGE>

CONFIDENTIAL TREATMENT

                                 AMENDMENT TWO
NOMOS Corporation                                   Radiation Treatment Planning
                                                                   Amendment Two
--------------------------------------------------------------------------------

         C.1.3      The License Issue Fee will not be credited against any other
                    royalty or fee due from LICENSEE to THE REGENTS.

         C.1.4      In the event that LICENSEE grants sublicenses, LICENSEE will
                    collect an issue fee equal to or greater than the License
                    Issue Fee. LICENSEE will pay to THE REGENTS [***] of any
                    issue fee from sublicensing.

C.2.     EARNED ROYALTIES

         In addition to the License Issue Fee, LICENSEE will pay THE REGENTS an
         earned royalty equal to [***] of Net Sales by LICENSEE and any
         sublicensees. The earned royalty on sales of any Licensed Product that
         is sold as part of a larger product system, shall be based on the
         average Net Sales of that Licensed Product sold separately on a non-OEM
         basis over the relevant royalty reporting period. For the purposes of
         calculating earned royalties, the minimum value of any License Product
         shall be [***] for the first two (2) full years after the date of
         initial release for distribution and offer of Sales of Licensed
         Products as specified in B.5.2. The minimum value shall be [***] for
         the next two (2) full years, and [***] thereafter.

         Payments of earned royalties will be in accordance with the
         requirements of Article 4.2 (SUBLICENSING RIGHTS AND OBLIGATIONS),
         Article 5 (FEES, ROYALTIES AND PAYMENTS) and Article 7 (PROGRESS AND
         ROYALTY REPORTS) of this Agreement.

---------------
***Confidential material redacted and filed separately with the Commission.

--------------------------------------------------------------------------------
                                       8

<PAGE>

CONFIDENTIAL TREATMENT

                                 AMENDMENT TWO

NOMOS Corporation                                   Radiation Treatment Planning
                                                            Amendment Two
--------------------------------------------------------------------------------

C.3  MINIMUM ANNUAL ROYALTIES

     LICENSEE will pay to THE REGENTS a minimum annual royalty according to the
requirements of Article 5 (FEES, ROYALTIES AND PAYMENTS) and the schedule
below. Earned royalties paid to THE REGENTS for Net Sales during a calendar
year will be accrued and credited against the minimum annual royalty paid for
that same calendar year.

--------------------------------------------------------------------------------
CALENDAR YEAR                    MINIMUM ANNUAL             DUE DATE IN CALENDAR
                                 ROYALTY                            YEAR
--------------------------------------------------------------------------------
    2000                         [***]                           February 28
--------------------------------------------------------------------------------
    2001                         [***]                           February 28
--------------------------------------------------------------------------------
    2002                         [***] of cumulative             February 28
                                 annual revenue* sales
                                 up to [***]

                                 [***] of cumulative
                                 annual revenue sales
                                 greater than [***]
                                 but less than
                                 [***]

                                 [***] of cumulative
                                 annual revenue sales
                                 greater than
                                 [***]
--------------------------------------------------------------------------------
    2003                         Same as 2002                    February 28
--------------------------------------------------------------------------------
    2004                         [***]                           February 28
--------------------------------------------------------------------------------
2005 and thereafter for the      [***]                           February 28
  life of this Agreement
--------------------------------------------------------------------------------

* As used herein, the term "cumulative annual revenue" means any revenue
generated from sales of the Licensed Products or use of the Licensed Methods,
accumulated or realized during the period January 1 to December 31 of a given
year, in this instance, the years 2002, and 2003.

---------------
***Confidential material redacted and filed separately with the Commission.

--------------------------------------------------------------------------------
                                       9

<PAGE>

CONFIDENTIAL TREATMENT

                                AMENDMENT TWO

NOMOS Corporation                                   Radiation Treatment Planning
                                                                   Amendment Two
--------------------------------------------------------------------------------

THE REGENTS and LICENSEE execute this Amendment, in duplicate originals, by
their respective officers who are duly authorized on the day and year that is
written.

NOMOS CORPORATION                            THE REGENTS OF THE
                                             UNIVERSITY OF CALIFORNIA

                                             LAWRENCE LIVERMORE
                                             NATIONAL LABORATORY

By:  /s/ Fred L. Marroni                     By: /s/ Karena McKinley
   ---------------------------------            -------------------------------
           (Signature)                                    (Signature)

Name:       Fred L. Marroni                  Name: Karena McKinley
     -------------------------------              -----------------------------

Title: VP - Engineering & Development        Title: Director, IPAC
      ------------------------------                ---------------------------

Date signed:  June 3            , 2002       Date signed:  June 4        , 2002
            --------------------                         ----------------

--------------------------------------------------------------------------------

                                       10

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