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. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2008-04-25 02:20:56.102 / Canadian Institutes of Health Research (CIHR) and the ORDCF’s Ontario Consortium for Image-guided Therapy and Surgery.

Cobalt-60 (Co-60) units played an integral role in radiation therapy from the mid-1950s to the 1970s. Although they continue to be used to treat cancer in some parts of the world, their role has been significantly reduced due to the invention of medical linear accelerators. A number of groups have indicated a strong potential for Co-60 units in modern radiation therapy. The Medical Physics group at the Cancer Center of the Southeastern Ontario and Queen’s University has shown the feasibility of Intensity Modulated Radiation Therapy (IMRT) via simple conformal treatment planning and dose delivery using a Co-60 unit. In this thesis, initial Co-60 tomotherapy planning investigations on simple uniform phantoms are extended to actual clinical cases based on patient CT data. The planning is based on radiation dose data from a clinical Co-60 unit fitted with a multileaf collimator (MLC) and modeled in the EGSnrc Monte Carlo system. An in house treatment planning program is used to calculate IMRT dose distributions. Conformal delivery in a single slice on a uniform phantom based on sequentially delivered pencil beams is verified by Gafchromic film. Volumetric dose distributions for Co-60 serial tomotherapy are then generated for typical clinical sites that had been treated at our clinic by conventional 6MV IMRT using Varian Eclipse treatment plans. The Co-60 treatment plans are compared with the clinical IMRT plans using conventional matrices such as dose volume histograms (DVH). Dose delivery based on simultaneously opened MLC leaves is also explored and a novel MLC segmentation method is proposed. In order to increase efficiency of dose calculations, a novel convolution based fluence model for treatment planning is also proposed. The ion chamber measurements showed that the Monte Carlo modeling of the beam data under the MIMiC MLC is accurate. The film measurements from the uniform phantom irradiations confirm that IMRT plans from our in-house treatment planning system are deliverable. Comparing the Co-60 dose distributions and DVHs to the IMRT plans from the clinic indicates that Co-60 is able to provide similar dose conformality to targets and dose sparing to critical organs. The results of the novel MLC segmentation algorithm and the photon fluence model proposed in this work compared well with the Monte Carlo calculations. In summary, the investigations presented in this thesis confirm that Co-60 tomotherapy is indeed capable of providing state-of-the-art conformal dose delivery. We have shown that the perceived beam limitations often identified with Co 60 (e.g., lower penetration, source size artifacts under small field collimation, and larger penumbra) are negligible when using intensity modulated techniques. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-08-22 11:34:14.861

Cobalt-60 (Co-60) units played an integral role in radiation therapy from the mid-1950s to the 1970s. Although they continue to be used to treat cancer in some parts of the world, their role has been significantly reduced due to the invention of medical linear accelerators. A number of groups have indicated a strong potential for Co-60 units in modern radiation therapy. The Medical Physics group at the Cancer Center of the Southeastern Ontario and Queen’s University has shown the feasibility of Intensity Modulated Radiation Therapy (IMRT) via simple conformal treatment planning and dose delivery using a Co-60 unit. In this thesis, initial Co-60 tomotherapy planning investigations on simple uniform phantoms are extended to actual clinical cases based on patient CT data. The planning is based on radiation dose data from a clinical Co-60 unit fitted with a multileaf collimator (MLC) and modeled in the EGSnrc Monte Carlo system. An in house treatment planning program is used to calculate IMRT dose distributions. Conformal delivery in a single slice on a uniform phantom based on sequentially delivered pencil beams is verified by Gafchromic film. Volumetric dose distributions for Co-60 serial tomotherapy are then generated for typical clinical sites that had been treated at our clinic by conventional 6MV IMRT using Varian Eclipse treatment plans. The Co-60 treatment plans are compared with the clinical IMRT plans using conventional matrices such as dose volume histograms (DVH). Dose delivery based on simultaneously opened MLC leaves is also explored and a novel MLC segmentation method is proposed. In order to increase efficiency of dose calculations, a novel convolution based fluence model for treatment planning is also proposed. The ion chamber measurements showed that the Monte Carlo modeling of the beam data under the MIMiC MLC is accurate. The film measurements from the uniform phantom irradiations confirm that IMRT plans from our in-house treatment planning system are deliverable. Comparing the Co-60 dose distributions and DVHs to the IMRT plans from the clinic indicates that Co-60 is able to provide similar dose conformality to targets and dose sparing to critical organs. The results of the novel MLC segmentation algorithm and the photon fluence model proposed in this work compared well with the Monte Carlo calculations. In summary, the investigations presented in this thesis confirm that Co-60 tomotherapy is indeed capable of providing state-of-the-art conformal dose delivery. We have shown that the perceived beam limitations often identified with Co 60 (e.g., lower penetration, source size artifacts under small field collimation, and larger penumbra) are negligible when using intensity modulated techniques. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-08-22 11:34:14.861