Exhibit 10.1

SECOND AMENDMENT TO EMPLOYMENT AGREEMENT
(Non CEO)

This Second Amendment to Employment Agreement is executed as of May 5, 2011, by and between TomoTherapy Incorporated, a Wisconsin corporation (the “Company”), and Thomas Rockwell Mackie, an individual (“Employee”), and amends that certain Employment Agreement between the Employee and Company entered into as of November 5, 2008, which was amended by the First Amendment effective July 1, 2009 (the “Agreement”).

RECITALS

The Company wishes to revise the provision of the Agreement limiting benefits payable in connection with a change in control, and the Employee agrees to such revised provision as set forth herein.

NOW, THEREFORE, in consideration of the premises and the mutual agreements and covenants contained herein, and for other good and valuable consideration, the receipt and sufficiency of which is hereby acknowledged by the Company and Employee,

IT IS HEREBY AGREED AS FOLLOWS:

1. Section 3.2(d) of the Agreement is amended to delete the words “, subject to Section 3.2(g)” as they appear therein.

2. Section 3.2(g) of the Agreement is deleted in its entirety and replaced by the following:

(g) Certain Additional Payments by the Company. (i) Anything in this Agreement to the contrary notwithstanding, in the event it shall be determined that any payment, distribution or benefit by the Company or its affiliated companies to or for the benefit of Employee (whether paid or payable or distributed or distributable pursuant to the terms of this Agreement or otherwise, but determined without regard to any additional payments required under this Section 3.2(g)) (a “Payment”) would be subject to the excise tax imposed by Section 4999 of the Code, or any interest or penalties are incurred by Employee with respect to such excise tax (such excise tax, together with any such interest and penalties, are hereinafter collectively referred to as the “Excise Tax”), then Employee shall be entitled to receive an additional payment (a “Gross-Up Payment”) in an amount such that after payment by Employee of all taxes (including any interest or penalties imposed with respect to such taxes), including, without limitation, any income taxes (and any interest and penalties imposed with respect thereto) and Excise Tax imposed upon the Gross-Up Payment, Employee retains an amount of the Gross-Up Payment equal to the Excise Tax imposed upon the Payments.

(ii) Subject to the provisions of Section 3.2(g)(iii), all determinations required to be made under this Section 3.2(g), including whether and when a Gross-Up Payment is required and the amount of such Gross-Up Payment and the assumptions to be utilized in arriving at such determination, shall be made by the Company’s public accounting firm (the “Accounting Firm”) which shall provide detailed supporting calculations both to the Company and Employee within 15 business

days of the receipt of notice from Employee that there has been a Payment, or such earlier time as is requested by the Company. In the event that the Accounting Firm is serving as accountant or auditor for the individual, entity or group effecting the Change of Control, Employee shall appoint another nationally recognized public accounting firm to make the determinations required hereunder (which accounting firm shall then be referred to as the Accounting Firm hereunder). All fees and expenses of the Accounting Firm shall be borne solely by the Company. Any Gross-Up Payment, as determined pursuant to this Section 3.2(g), shall be paid by the Company to Employee within five days of the receipt of the Accounting Firm’s determination, but in no event later than the last day of the calendar year following the calendar year in which the related tax is remitted to the Internal Revenue Service. If the Accounting Firm determines that no Excise Tax is payable by Employee, it shall furnish Employee with a written opinion that failure to report the Excise Tax on Employee’s applicable federal income tax return would not result in the imposition of a negligence or similar penalty. Any determination by the Accounting Firm shall be binding upon the Company and Employee. As a result of the uncertainty in the application of Section 4999 of the Code at the time of the initial determination by the Accounting Firm hereunder, it is possible that Gross-Up Payments which will not have been made by the Company should have been made (“Underpayment”), consistent with the calculations required to be made hereunder. In the event that the Company exhausts its remedies pursuant to Section 3.2(g)(iii) and Employee thereafter is required to make a payment of any Excise Tax, the Accounting Firm shall determine the amount of the Underpayment that has occurred and any such Underpayment shall be promptly paid by the Company to or for the benefit of Employee.

(iii) Employee shall notify the Company in writing of any claim by the Internal Revenue Service that, if successful, would require the payment by the Company of the Gross-Up Payment. Such notification shall be given as soon as practicable but no later than 10 business days after Employee is informed in writing of such claim and shall apprise the Company of the nature of such claim and the date on which such claim is requested to be paid. Employee shall not pay such claim prior to the expiration of the 30-day period following the date on which Employee gives such notice to the Company (or such shorter period ending on the date that any payment of taxes with respect to such claim is due). If the Company notifies Employee in writing prior to the expiration of such period that it desires to contest such claim, Employee shall:

(A) give the Company any information reasonably requested by the Company relating to such claim,

(B) take such action in connection with contesting such claim as the Company shall reasonably request in writing from time to time, including, without limitation, accepting legal representation with respect to such claim by an attorney reasonably selected by the Company,

(C) cooperate with the Company in good faith in order effectively to contest such claim, and

(D) permit the Company to participate in any proceedings relating to such claim;

provided, however, that the Company shall bear and pay directly all costs and expenses (including additional interest and penalties) incurred in connection with such contest and shall

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indemnify and hold Employee harmless, on an after-tax basis, for any Excise Tax or income tax (including interest and penalties with respect thereto) imposed as a result of such representation and payment of costs and expenses. Without limitation on the foregoing provisions of this Section 3.2(g)(iii), the Company shall control all proceedings taken in connection with such contest and, at its sole option, may pursue or forgo any and all administrative appeals, proceedings, hearings and conferences with the taxing authority in respect of such claim and may, at its sole option, either direct Employee to pay the tax claimed and sue for a refund or contest the claim in any permissible manner, and Employee agrees to prosecute such contest to a determination before any administrative tribunal, in a court of initial jurisdiction and in one or more appellate courts, as the Company shall determine; provided further, that if the Company directs Employee to pay such claim and sue for a refund, the Company shall advance the amount of such payment to Employee on an interest-free basis and shall indemnify and hold Employee harmless, on an after-tax basis, from any Excise Tax or income tax (including interest or penalties with respect thereto) imposed with respect to such advance or with respect to any imputed income with respect to such advance; and provided further, that any extension of the statute of limitations relating to payment of taxes for the taxable year of Employee with respect to which such contested amount is claimed to be due is limited solely to such contested amount. Furthermore, the Company’s control of the contest shall be limited to issues with respect to which a Gross-Up Payment would be payable hereunder and Employee shall be entitled to settle or contest, as the case may be, any other issue raised by the Internal Revenue Service or any other taxing authority.

(iv) If, after the receipt by Employee of an amount advanced by the Company pursuant to Section 3.2(g), Employee becomes entitled to receive, and receives, any refund with respect to such claim, Employee shall (subject to the Company’s complying with the requirements of Section 3.2(g)(iii)) promptly pay to the Company the amount of such refund (together with any interest paid or credited thereon after taxes applicable thereto). If, after the receipt by Employee of an amount advanced by the Company pursuant to Section 3.2(g)(iii), a determination is made that Employee shall not be entitled to any refund with respect to such claim and the Company does not notify Employee in writing of its intent to contest such denial of refund prior to the expiration of 30 days after such determination, then such advance shall be forgiven and shall not be required to be repaid and the amount of such advance shall offset, to the extent thereof, the amount of Gross-Up Payment required to be paid.

3. All other provisions of the Agreement are not altered by this Second Amendment and remain in full force and effect.

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IN WITNESS WHEREOF, the parties have executed this Amendment as of the day and year written above.