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Delivery of external beam radiation therapy usually requires relative rotation between the radiation source and the patient. Typically this is achieved by rotating the radiation around the patient using a gantry. An alternative approach is to instead rotate a patient relative to a stationary radiation source i.e. gantry-free radiotherapy. Removing the requirement of a rotating gantry would reduce the costs and space requirements for proton and heavy ion facilities, enable cheaper x-ray systems, facilitate synchrotron-based x-ray treatments and offer a much more practical approach for integrating MRI with proton treatments in the future. In this thesis, four studies were performed to address key barriers to gantry-free RT. Anatomical changes caused by rotation need to be considered for gantry-free treat- ments. In chapter 3, global pelvic rigid and non-rigid deformation was quantified for a cohort of 8 healthy participants rotated 360 degrees in 45-degree increments within a radiotherapy dedicated MRI scanner. Rigid translations of the participants between 5.8 – 30.0 mm were observed, which were most substantial in the left-right direction. Maximum displacement occurred at the 90 and 270 degree couch angles. Non-rigid deformation was greatest around the external body surface, up to 28.0 mm in mag- nitude for some participants. Internal prostate, rectum and bladder motion was then compared to the supine position for a cohort of 9 prostate cancer patients in chapter 4. Organ motion was largest at the 180-degree (prone) couch position. Prostate motion was < 2 mm in the left-right direction, 0 – 14 mm in the superior-inferior direction and -11 – 4 mm in the anterior-posterior direction.

The integration of online magnetic resonance imaging with linear accelerators presents an exciting new era for radiation therapy. A hybrid MRI-linac machine provides improved soft-tissue contrast enabling the target to be visualised at the time of treatment rather than a surrogate, as is currently common practice. With this advancement comes a number of unique challenges related to the presence of a magnetic field during treatment, one of which is the change in the dose distribution. The magnetic field’s associated force vector, the Lorentz force, influences the trajectory of charged particles within it. Dose-depositing secondary electrons are no exception. Using Monte Carlo simulations, point spread dose arrays have been modelled to demonstrate on a fundamental level how dose distributions are perturbed by magnetic fields as a function of magnetic field strength, orientation with respect to the primary beam and the density of the medium. For the case of inline magnetic fields, the point spread distribution maintains its symmetry, but lengthens and becomes more narrow laterally.

The integration of online magnetic resonance imaging with linear accelerators presents an exciting new era for radiation therapy. A hybrid MRI-linac machine provides improved soft-tissue contrast enabling the target to be visualised at the time of treatment rather than a surrogate, as is currently common practice. With this advancement comes a number of unique challenges related to the presence of a magnetic field during treatment, one of which is the change in the dose distribution. The magnetic field’s associated force vector, the Lorentz force, influences the trajectory of charged particles within it. Dose-depositing secondary electrons are no exception. Using Monte Carlo simulations, point spread dose arrays have been modelled to demonstrate on a fundamental level how dose distributions are perturbed by magnetic fields as a function of magnetic field strength, orientation with respect to the primary beam and the density of the medium. For the case of inline magnetic fields, the point spread distribution maintains its symmetry, but lengthens and becomes more narrow laterally.

The integration of online magnetic resonance imaging with linear accelerators presents an exciting new era for radiation therapy. A hybrid MRI-linac machine provides improved soft-tissue contrast enabling the target to be visualised at the time of treatment rather than a surrogate, as is currently common practice. With this advancement comes a number of unique challenges related to the presence of a magnetic field during treatment, one of which is the change in the dose distribution. The magnetic field’s associated force vector, the Lorentz force, influences the trajectory of charged particles within it. Dose-depositing secondary electrons are no exception. Using Monte Carlo simulations, point spread dose arrays have been modelled to demonstrate on a fundamental level how dose distributions are perturbed by magnetic fields as a function of magnetic field strength, orientation with respect to the primary beam and the density of the medium. For the case of inline magnetic fields, the point spread distribution maintains its symmetry, but lengthens and becomes more narrow laterally.

The integration of online magnetic resonance imaging with linear accelerators presents an exciting new era for radiation therapy. A hybrid MRI-linac machine provides improved soft-tissue contrast enabling the target to be visualised at the time of treatment rather than a surrogate, as is currently common practice. With this advancement comes a number of unique challenges related to the presence of a magnetic field during treatment, one of which is the change in the dose distribution. The magnetic field’s associated force vector, the Lorentz force, influences the trajectory of charged particles within it. Dose-depositing secondary electrons are no exception. Using Monte Carlo simulations, point spread dose arrays have been modelled to demonstrate on a fundamental level how dose distributions are perturbed by magnetic fields as a function of magnetic field strength, orientation with respect to the primary beam and the density of the medium. For the case of inline magnetic fields, the point spread distribution maintains its symmetry, but lengthens and becomes more narrow laterally.

The integration of online magnetic resonance imaging with linear accelerators presents an exciting new era for radiation therapy. A hybrid MRI-linac machine provides improved soft-tissue contrast enabling the target to be visualised at the time of treatment rather than a surrogate, as is currently common practice. With this advancement comes a number of unique challenges related to the presence of a magnetic field during treatment, one of which is the change in the dose distribution. The magnetic field’s associated force vector, the Lorentz force, influences the trajectory of charged particles within it. Dose-depositing secondary electrons are no exception. Using Monte Carlo simulations, point spread dose arrays have been modelled to demonstrate on a fundamental level how dose distributions are perturbed by magnetic fields as a function of magnetic field strength, orientation with respect to the primary beam and the density of the medium. For the case of inline magnetic fields, the point spread distribution maintains its symmetry, but lengthens and becomes more narrow laterally.

The integration of online magnetic resonance imaging with linear accelerators presents an exciting new era for radiation therapy. A hybrid MRI-linac machine provides improved soft-tissue contrast enabling the target to be visualised at the time of treatment rather than a surrogate, as is currently common practice. With this advancement comes a number of unique challenges related to the presence of a magnetic field during treatment, one of which is the change in the dose distribution. The magnetic field’s associated force vector, the Lorentz force, influences the trajectory of charged particles within it. Dose-depositing secondary electrons are no exception. Using Monte Carlo simulations, point spread dose arrays have been modelled to demonstrate on a fundamental level how dose distributions are perturbed by magnetic fields as a function of magnetic field strength, orientation with respect to the primary beam and the density of the medium. For the case of inline magnetic fields, the point spread distribution maintains its symmetry, but lengthens and becomes more narrow laterally.

The integration of online magnetic resonance imaging with linear accelerators presents an exciting new era for radiation therapy. A hybrid MRI-linac machine provides improved soft-tissue contrast enabling the target to be visualised at the time of treatment rather than a surrogate, as is currently common practice. With this advancement comes a number of unique challenges related to the presence of a magnetic field during treatment, one of which is the change in the dose distribution. The magnetic field’s associated force vector, the Lorentz force, influences the trajectory of charged particles within it. Dose-depositing secondary electrons are no exception. Using Monte Carlo simulations, point spread dose arrays have been modelled to demonstrate on a fundamental level how dose distributions are perturbed by magnetic fields as a function of magnetic field strength, orientation with respect to the primary beam and the density of the medium. For the case of inline magnetic fields, the point spread distribution maintains its symmetry, but lengthens and becomes more narrow laterally.

The Australian MRI-Linac consists of a fixed horizontal photon beam combined with a MRI. Commissioning required PDD and profiles measured in a horizontal set-up using a combination of water tank measurements and gafchromic film. To validate the methodology, measurements were performed comparing PDD and profiles measured with the gantry angle set to 0 and 90° on a conventional linac. Results showed agreement to within 2.0% for PDD measured using both film and the water tank at gantry 90° relative to PDD acquired using gantry 0°. Profiles acquired using a water tank at both gantry 0 and 90° showed agreement in FWHM to within 1 mm. The agreement for both PDD and profiles measured at gantry 90° relative to gantry 0° curves indicates that the methodology described can be used to acquire the necessary beam data for horizontal beam lines and in particular, commissioning the Australian MRI-linac.

The Australian MRI-Linac consists of a fixed horizontal photon beam combined with a MRI. Commissioning required PDD and profiles measured in a horizontal set-up using a combination of water tank measurements and gafchromic film. To validate the methodology, measurements were performed comparing PDD and profiles measured with the gantry angle set to 0 and 90° on a conventional linac. Results showed agreement to within 2.0% for PDD measured using both film and the water tank at gantry 90° relative to PDD acquired using gantry 0°. Profiles acquired using a water tank at both gantry 0 and 90° showed agreement in FWHM to within 1 mm. The agreement for both PDD and profiles measured at gantry 90° relative to gantry 0° curves indicates that the methodology described can be used to acquire the necessary beam data for horizontal beam lines and in particular, commissioning the Australian MRI-linac.

The Australian MRI-Linac consists of a fixed horizontal photon beam combined with a MRI. Commissioning required PDD and profiles measured in a horizontal set-up using a combination of water tank measurements and gafchromic film. To validate the methodology, measurements were performed comparing PDD and profiles measured with the gantry angle set to 0 and 90° on a conventional linac. Results showed agreement to within 2.0% for PDD measured using both film and the water tank at gantry 90° relative to PDD acquired using gantry 0°. Profiles acquired using a water tank at both gantry 0 and 90° showed agreement in FWHM to within 1 mm. The agreement for both PDD and profiles measured at gantry 90° relative to gantry 0° curves indicates that the methodology described can be used to acquire the necessary beam data for horizontal beam lines and in particular, commissioning the Australian MRI-linac.

The Australian MRI-Linac consists of a fixed horizontal photon beam combined with a MRI. Commissioning required PDD and profiles measured in a horizontal set-up using a combination of water tank measurements and gafchromic film. To validate the methodology, measurements were performed comparing PDD and profiles measured with the gantry angle set to 0 and 90° on a conventional linac. Results showed agreement to within 2.0% for PDD measured using both film and the water tank at gantry 90° relative to PDD acquired using gantry 0°. Profiles acquired using a water tank at both gantry 0 and 90° showed agreement in FWHM to within 1 mm. The agreement for both PDD and profiles measured at gantry 90° relative to gantry 0° curves indicates that the methodology described can be used to acquire the necessary beam data for horizontal beam lines and in particular, commissioning the Australian MRI-linac.

PURPOSE:Magnetic fields are known to alter radiation dose deposition. Before patients receive treatment using an MRI-linear accelerator (MRI-Linac), preclinical studies are needed to understand the biological consequences of magnetic-field-induced dose effects. In the present study, the authors sought to identify a beam energy and magnetic field strength combination suitable for preclinical murine experiments. METHODS:Magnetic field dose effects were simulated in a mouse lung phantom using various beam energies (225 kVp, 350 kVp, 662 keV [Cs-137], 2 MV, and 1.25 MeV [Co-60]) and magnetic field strengths (0.75, 1.5, and 3 T). The resulting dose distributions were compared with those in a simulated human lung phantom irradiated with a 6 or 8 MV beam and orthogonal 1.5 T magnetic field. RESULTS:In the human lung phantom, the authors observed a dose increase of 45% and 54% at the soft-tissue-to-lung interface and a dose decrease of 41% and 48% at the lung-to-soft-tissue interface for the 6 and 8 MV beams, respectively. In the mouse simulations, the magnetic fields had no measurable effect on the 225 or 350 kVp dose distribution. The dose increases with the Cs-137 beam for the 0.75, 1.5, and 3 T magnetic fields were 9%, 29%, and 42%, respectively. The dose decreases were 9%, 21%, and 37%. For the 2 MV beam, the dose increases were 16%, 33%, and 31% and the dose decreases were 9%, 19%, and 30%. For the Co-60 beam, the dose increases were 19%, 54%, and 44%, and the dose decreases were 19%, 42%, and 40%. CONCLUSIONS:The magnetic field dose effects in the mouse phantom using a Cs-137, 3 T combination or a Co-60, 1.5 or 3 T combination most closely resemble those in simulated human treatments with a 6 MV, 1.5 T MRI-Linac. The effects with a Co-60, 1.5 T combination most closely resemble those in simulated human treatments with an 8 MV, 1.5 T MRI-Linac.

PURPOSE:Magnetic fields are known to alter radiation dose deposition. Before patients receive treatment using an MRI-linear accelerator (MRI-Linac), preclinical studies are needed to understand the biological consequences of magnetic-field-induced dose effects. In the present study, the authors sought to identify a beam energy and magnetic field strength combination suitable for preclinical murine experiments. METHODS:Magnetic field dose effects were simulated in a mouse lung phantom using various beam energies (225 kVp, 350 kVp, 662 keV [Cs-137], 2 MV, and 1.25 MeV [Co-60]) and magnetic field strengths (0.75, 1.5, and 3 T). The resulting dose distributions were compared with those in a simulated human lung phantom irradiated with a 6 or 8 MV beam and orthogonal 1.5 T magnetic field. RESULTS:In the human lung phantom, the authors observed a dose increase of 45% and 54% at the soft-tissue-to-lung interface and a dose decrease of 41% and 48% at the lung-to-soft-tissue interface for the 6 and 8 MV beams, respectively. In the mouse simulations, the magnetic fields had no measurable effect on the 225 or 350 kVp dose distribution. The dose increases with the Cs-137 beam for the 0.75, 1.5, and 3 T magnetic fields were 9%, 29%, and 42%, respectively. The dose decreases were 9%, 21%, and 37%. For the 2 MV beam, the dose increases were 16%, 33%, and 31% and the dose decreases were 9%, 19%, and 30%. For the Co-60 beam, the dose increases were 19%, 54%, and 44%, and the dose decreases were 19%, 42%, and 40%. CONCLUSIONS:The magnetic field dose effects in the mouse phantom using a Cs-137, 3 T combination or a Co-60, 1.5 or 3 T combination most closely resemble those in simulated human treatments with a 6 MV, 1.5 T MRI-Linac. The effects with a Co-60, 1.5 T combination most closely resemble those in simulated human treatments with an 8 MV, 1.5 T MRI-Linac.