Title page for ETD etd-08302006-123936

Type of Document Master's Thesis
Author Ashenafi, Michael Sissay
Author's Email Address mashen1@lsu.edu, michaeleth@gmail.com
URN etd-08302006-123936
Title TomoTherapy for Post-Mastectomy Radiotherapy (PMRT): Comparison with Conventional Electron Beam Technique
Degree Master of Science (M.S.)
Department Physics & Astronomy
Advisory Committee
Advisor Name Title
Robert A. Boyd Committee Chair
Kenneth R. Hogstrom Committee Co-Chair
Gregory Stacy Committee Member
John P. Gibbons Committee Member
  • treatment planning
  • tomotherapy
  • intensity modulated radiation therapy
  • chest wall
  • electron radiation therapy
  • postmastectomy radiation therapy
Date of Defense 2006-06-11
Availability unrestricted
Purpose: TomoTherapy, capable of delivering intensity-modulated, image-guided radiotherapy with a helical fan-beam, multileaf-collimated beam and detector array mounted on a CT ring, is challenging the treatment techniques commonly used in today's radiotherapy clinic. The present works investigates the potential of using TomoTherapy in lieu of electron beams for treatment of the chest wall in post-mastectomy radiotherapy (PMRT). It is hypothesized that TomoTherapy can plan dose distributions for PMRT patients, that a pre-selected radiation oncologist judges to be equal to or better than that of a conventional plan treated with electron beams.

Methods: A patient database of retrospective conventional PMRT treatment plans was generated, including contoured target and critical structure region-of-interest volumes. A TomoTherapy plan was generated for five patients out of the database using the same treatment criteria as the conventional plan. The TomoTherapy plan and the conventional plan was evaluated and compared by a radiation oncologist using a simplified scoring system. Physical and radiobiological dose metrics were generated from the treatment plans to supplement the evaluation of the radiation oncologist.

Results: Four of the five TomoTherapy plans were rated superior to the rival conventional electron beam treatment plan, and the other Tomotherapy plan was rated marginally superior. The TomoTherapy plan was able to spare the ipsilateral lung and heart of excessive dose as well as the conventional plan, while delivering a more homogeneous dose distribution to the target volumes. However, the TomoTherapy plan showed the contralateral breast receiving an average dose of 2.9 Gy as opposed to 0.4 Gy for the conventional electron beam plan, and a greater volume of normal tissue outside the target volumes receiving dose between 5 and 25 Gy (average percent volume was 33% for the TomoTherapy plan and 5 % for the electron beam plan). This could affect the radiation oncologist's decision to use TomoTherapy for younger patients who are at greater risk of developing radiation-induced secondary cancers.

Conclusion: The study showed TomoTherapy can deliver dose distributions the radiation oncologist judges to be equal to or better than that of a conventional electron beam PMRT plan for five treatment plans.

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