Document:

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                                                                   Exhibit 10.21

June 29, 2001

Russell Johnson
49 Campbell Lane
Menlo Park, CA 94025

Re:  Separation Agreement Including A General Release

Dear Russ:

     This letter sets forth the terms of our agreement with respect to your
separation from employment with RITA Medical Systems, Inc. ("COMPANY").

     Your final date of active employment with Company will be June 30, 2001. As
of that date, except as specifically provided in this Agreement, all
compensation, including bonuses, and all other benefits and perquisites of
employment will cease. You will receive your regular base pay through that date
less authorized and required deductions.

     You may elect to continue your medical coverage at the prevailing active
employee rate(s) as provided by the Consolidated Omnibus Budget Reconciliation
Act of 1986 ("COBRA"). Additional information concerning your COBRA rights will
be provided separately.

     If the terms of this Agreement are accepted by you and if you return a
fully executed original of this Agreement as described below and all Company
property in your possession, as described below, by July 20, 2001, following
your compliance with the above conditions, you will be entitled to the
following:

     (1)  Salary continuation payments in an amount equal to your regular salary
          as of June 30, 2001 less authorized and required deductions; for a
          period of two and one half months, from July 1, 2001 until September
          14, 2001. These salary continuation payments shall be paid in
          semi-monthly installments on Company regular paydays. This shall
          include the use of your accrued vacation time, estimated to be 72
          hours by September 14, 2001. Any remaining hours will be paid out with
          your September 14 pay.

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     (2)  The right to retain the laptop computer currently in your possession,
          plus access to Company e-mail and voice mail systems through September
          14, 2001.

     (3)  Continued vacation accrual and stock option vesting through September
          14, 2001.

     (4)  The Company will continue your health care benefits at the group rate
          through September 30, 2001. After that time, you may elect to continue
          them on your own through COBRA.

     In return for the payments and other benefits described above, which you
acknowledge exceed the amount to which you otherwise are entitled under Company
policies and practices, you and your representatives completely release Company
and its present and former directors, officers, and employees from all claims of
any kind, known and unknown, which you may now have or have ever had against
Company, including claims for compensation, bonuses, severance pay, stock
options, and all claims arising from your employment with Company or the
termination of your employment, whether based on contract, tort, statute, local
ordinance, regulation or any comparable law in any jurisdiction ("Released
Claims"). By way of example and not in limitation, the Released Claims shall
include any claims arising under Title VII of the Civil Rights Act of 1964, the
Americans with Disabilities Act, and the California Fair Employment and Housing
Act, as well as any claims asserting wrongful termination, breach of contract,
breach of the covenant of good faith and fair dealing, negligent or intentional
infliction of emotional distress, negligent or intentional misrepresentation,
negligent or intentional interference with contract or prospective economic
advantage, and defamation.

     You acknowledge and understand that the release of claims under the Age
Discrimination in Employment Act ("ADEA"), 29 U.S.C. ss.ss. 621-634, is subject
to special waiver protection under 29 U.S.C. ss. 626 (f). In accordance with
that section, you specifically agree that you knowingly and voluntarily release
and waive any rights or claims of discrimination under the ADEA. In particular,
you represent that you have carefully read this Agreement in its entirety, that
you have had an opportunity to consider fully the terms of this Agreement for
twenty-one (21) days and that you have seven (7) days after you sign this
Agreement in which to revoke this Agreement, and that you have been advised by
Company to consult with an attorney of your choosing in connection with this
Agreement, that you have discussed the Agreement with your independent legal
counsel, or have had a reasonable opportunity to do so and that you are signing
this agreement voluntarily and of your own free will.

                                                                               2

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     You agree that because these releases specifically cover known and unknown
claims, you waive your rights under Section 1542 of the California Civil Code,
or under any comparable law of any jurisdiction. Section 1542 states:

     "A general release does not extend to claims which the creditor does not
     know or suspect to exist in his favor at the time of executing the release,
     which if known by him must have materially affected his settlement with the
     debtor."

     You agree not to disclose any confidential, proprietary or know-how
belonging to Company or acquired by you during your employment with Company as
described in the Confidential Information And Invention Assignment Agreement
("Non-Disclosure Agreement"). You acknowledge that the Non-Disclosure Agreement
entered into by you on June 24,1998 remains in effect after your employment with
Company ends.

     You represent that you have returned to Company all Company property
(including without limitation, keys to all offices and facilities, mobile
telephones, employee handbooks, business cards, client files, corporate credit
cards, telephone calling cards, files, sales material) in your possession and
you have not retained any reproductions of these items.

     This Agreement shall be governed by the laws of the State of California and
the parties in any action arising from this Agreement shall be subject to the
jurisdiction and venue of the federal and state courts, as applicable, in the
County of Santa Clara, State of California.

     You understand and agree that this Agreement shall be maintained in strict
confidence, and that you shall not disclose this Agreement or any of its terms
to any other person unless required by law.

     You and the Company further agree that any and all disputes arising out of
the terms, interpretation, application, or alleged breach of this Agreement
shall be subject to binding arbitration, which shall be conducted in Santa Clara
County, California, in accordance with the National Rules for the Resolution of
Employment Disputes of the American Arbitration Association, as amended. The
costs of the arbitrator shall be shared equally between the parties. If any
legal or equitable action or arbitration is necessary to enforce the terms of
this Agreement, the prevailing party shall be entitled to a reasonable sum for
attorneys' fees and costs.

     You and Company also agree that this letter contains all of our agreements
and understandings, and fully supersedes any prior agreements or

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understandings that we may have had regarding the subject matter of this
Agreement.

     Finally, by your signature below, you acknowledge each of the following:
(a) that you have read this Agreement or have been afforded every opportunity to
do so; (b) that you are fully aware of the Agreement's contents and legal
effect; and (c) that you have chosen to enter into this Agreement freely,
without coercion and based upon your own judgment and not in reliance upon any
promises made by Company other than those contained in this letter.

     If this letter comports with your understanding of our Agreement, please
sign on the line provided below and return the original to Harriet Bell, HR
Director in a confidential envelope by July 20, 2001.

                                   Sincerely,

                                   /s/ Donald Stewart
                                   ----------------------------
                                   Donald Stewart, CFO
                                   For RITA Medical Systems, Inc.

     I have read and understand the Agreement above and agree to be bound by its
terms and conditions.

/s/ Russell Johnson                                January 21, 2001
---------------------------                        -----------------------------
Name                                               Date<PAGE>

                                                                   Exhibit 10.22

                               AMENDMENT TO LEASE
                               ------------------

                          967 North Shoreline Boulevard
                            Mountain View, California

     THIS AMENDMENT TO LEASE (this "Amendment") is dated for reference purposes
June 4, 2001 by and between 967 SHORELINE ASSOCIATES, L.P., a California limited
partnership, successor in interest to Brown Mountain View Joint Venture, a
California Joint Venture ("Lessor"), and RITA MEDICAL SYSTEMS, INC., a Delaware
corporation, successor to ZoMed International ("Lessee").

                                    RECITALS
                                    --------

     A. Brown Mountain View Joint Venture, as Lessor, and Lessee entered into a
Standard Industrial/Commercial Single-Tenant Lease - Net dated July 12, 1994
(the "Lease") of approximately 18,000 square feet of office/R&D space in a
freestanding building (the "Premises") of the real property commonly referred to
as 967 Shoreline Boulevard, Mountain View, California. The term of the Lease
commenced on August 15, 1994. The Lease was extended to August 14, 2004 by
letter agreement dated May 12, 1999. Lessee is currently in possession of the
Premises. 967 Shoreline Associates, L.P. is successor to Brown Mountain View
Joint Venture.

     B. Lessor and Lessee wish to enter into this Amendment to reflect their
agreement with respect to reinstating and amending the provisions of Paragraph
49 - Option to Extend in the Lease, as set forth herein.

                                    AGREEMENT
                                    ---------

     NOW THEREFORE, in consideration of the mutual covenants of the parties
contained herein, and other good and valuable consideration, the receipt and
adequacy of which are hereby acknowledged, the parties agree as follows:

     1. Defined Terms. Terms defined in the Lease shall have the same meaning in
        -------------
this Amendment as they have in the Lease.

     2. Option to Extend. Paragraph 49, of the Lease is hereby reinstated and
        ----------------
Paragraph 9(a) Grant of Option is amended to modify the option term from (5)
years to (4) years. Upon exercise of Option, the Extended Term shall be August
15, 2004 through August 14, 2008.

     3. Continuing Effect. Except as amended hereby, the Lease remains in full
        -----------------
force and effect.

     4. Counterparts. This Amendment may be executed in one or more
        ------------
counterparts, each of which shall be deemed an original but all of which shall
constitute one and the same instrument.

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     IN WITNESS WHEREOF, the parties have executed this Amendment to Lease on
the dates shown opposite their signatures below.

                                    "Lessor"

                                    967 SHORELINE ASSOCIATES, L.P.,
                                    a California limited partnership

                                    By:  Vance Brown, Inc.
                                         A California corporation,
                                         Its General Partner

June 13           , 2001            By:  /s/ Ray Freschi
------------------                     ---------------------------------------
                                       Its Property Manager

                                    "Lessee"

                                    RITA MEDICAL SYSTEMS, INC.
                                    A Delaware corporation

June 12           , 2001            By: /s/  Ronald Steckel
------------------                     ---------------------------------------
                                       Its Senior Vice President

                  , 2001            By:
------------------                     ---------------------------------------
                                       Its

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