AMENDED AND RESTATED NOTE AND EQUITY PURCHASE AGREEMENT

Exhibit 10.4.5

AMENDMENT NO. 4

to the

AMENDED AND RESTATED

NOTE AND EQUITY PURCHASE AGREEMENT

by and among

GLOBAL DOSIMETRY SOLUTIONS, INC.,

AMERICAN CAPITAL FINANCIAL SERVICES, INC.,

AS AGENT

and

THE PURCHASERS IDENTIFIED ON
ANNEX A HERETO

Date of Amendment No. 4: December 15, 2006
Date of Amendment No. 3: March 28, 2006
Date of Amendment No. 2: February 1, 2006
Date of Amendment No. 1: October 14, 2005

AMENDMENT NO. 4
to the
AMENDED AND RESTATED
NOTE AND EQUITY PURCHASE AGREEMENT

     THIS AMENDMENT NO. 4, dated as of December 15, 2006 (this “ Amendment No. 4 ”), amends the Amended and Restated Note and Equity Purchase Agreement, dated November 10, 2004 (as amended to date, the “ Agreement ”), and is made by and among Global Dosimetry Solutions, Inc., a Delaware corporation (the “ Company ”), the securities purchasers that are now and hereafter at any time parties thereto and are listed in Annex A (or any amendment or supplement thereto) attached thereto (each a “ Purchaser ” and collectively, “ Purchasers ”), and American Capital Financial Services, Inc., a Delaware corporation (“ ACFS ”), as administrative agent for Purchasers (in such capacity “ Agent ”).

RECITALS

     A. The parties hereto were party to a Note and Equity Purchase Agreement, dated as of September 30, 2003 (the “ Original Purchase Agreement ”);

     B. The parties hereto are party to the Agreement, pursuant to which the Original Purchase Agreement was amended and restated;

     C. The Company, Purchasers and the Agent have agreed to enter into this Amendment No. 4 to amend certain terms of the Agreement.

     NOW, THEREFORE, the parties hereto, in consideration of the foregoing premises and their mutual covenants and agreements herein set forth and intending to be legally bound hereby, covenant and agree as follows:

1. Definitions . Capitalized terms used and not defined elsewhere in this Amendment are as defined in the Agreement.

2. Amendments . The Agreement is hereby amended as follows:

     (a) The following definitions set forth in Section 1.1 of the Agreement are hereby amended and restated in their entirety as follows:

     “Revolving Loan Commitment Amount” shall mean $14,000,000.

     “Revolving Loan Rate” shall mean a rate per annum equal to the LIBOR Rate plus 5.0%.

     (b) Section 3.8(b) is hereby amended and restated as follows:

     “(b) [Intentionally omitted.]”

3. Representations and Warranties . The Company hereby represents and warrants as follows: