The application of electron beam delivery using dose rate variation and dynamic couch motion in conformal treatment of the cranial-spinal axis

Radiation therapy to the cranial-spinal axis is typically targeted to the spinal cord and to the cerebrospinal fluid (CSF) in the subarachnoid space adjacent to the spinal cord and brain. Standard techniques employed in the treatment of the whole central nervous system do little to compensate for the varying depths of spinal cord along the length of the spinal field. Lateral simulation films, sagittal magnetic resonance imaging (MRI), or computerized tomography (CT) are used to estimate an average prescription depth for treatment along the spine field. However, due to the varying depth of the target along the spinal axis, even with the use of physical compensators, there can be considerable dose inhomogeneity along the spine field. With the advent of treatment machines that have full dynamic capabilities, a technique has been devised that will allow for more conformal dose distribution along the full length of the spinal field. This project simulates this technique utilizing computer-controlled couch motion to deliver multiple small electron beams of differing energies and intensities. CT planning determines target depth along the entire spine volume. The ability to conform dose along the complete length of the treatment field is investigated through the application of superpositioning of the fields as energies and intensities change. The positioning of each beam is registered with the treatment couch dynamic motion. This allows for 1 setup in the treatment room rather than multiple setups for each treatment position, which would have been previously required. Dose-volume histograms are utilized to evaluate the dose delivered to structures in the beam exit region. This technique will allow for precise localization and delivery of a homogeneous dose to the entire CSF space