Conformal Radiation Therapy with Cobalt-60 Tomotherapy

Abstract

Intensity-modulated radiation therapy (IMRT) is an advanced mode of high- precision radiation therapy that utilizes computer-controlled x-ray accelerators to deliver precise radiation doses to malignant tumors. The radiation dose is designed to conform to the three-dimensional (3-D) shape of a tumor by modulating the intensity of the radiation beam to focus a higher radiation dose to the tumor while minimizing radiation exposure to surrounding normal tissue. One form of IMRT is known as tomotherapy. Tomotherapy achieves dose conformity to a tumor by modulating the intensity of a fan beam of radiation as the source revolves about a patient. Current available tomotherapy machines use x-ray linear accelerators (linacs) as a source of radiation. However, since linacs are technologically complex, the world- wide use of linac-based tomotherapy is limited. This thesis involves an investigation of Cobalt 60 (Co-60) based tomotherapy. The inherent simplicity of Co-60 has the potential to extend the availability of this technique to clinics throughout the world. The goal of this thesis is to generate two-dimensional (2-D) Co-60 tomotherapy con- formal dose distributions with a computer program and experimentally validate them on ¯lm using a ¯rst generation bench-top tomotherapy apparatus. The bench-top apparatus consists of a rotation-translation stage that can mimic a 2-D tomotherapy delivery by translating the phantom across a thin, "pencil- like" photon beam from various beam orientations. In this thesis, several random and clinical patterns are planned using an in-house inverse treatment planning system and are delivered on ¯lm using the tomotherapy technique. The delivered dose plans are compared with the simulated plans using the gamma dose comparison method. The results show a reasonably good agreement between the plans and the measurements, suggesting that Co-60 tomotherapy is indeed capable of providing state-of-the-art conformal dose delivery.