Meaghen Shiha (Carleton University)
Dosimetric impact of intra-fraction motion on hypo-fractionated radiation therapy
The spine is one of the most common sites for cancer metastases. These metastases are often painful and can lead to complications such as vertebral fractures and spinal cord compression. Radiation therapy is a common palliative treatment for these types of metastases. Stereotactic Body Radiation Therapy (SBRT) is a technique where large doses are delivered in a small number of treatment fractions to a target. For patients with spinal metastases, SBRT has been shown to provide better pain relief compared to conventional radiation therapy. Due to the high doses delivered and proximity to the spinal cord, there are stringent patient immobilization and intra-fraction imaging requirements for SBRT delivery. This presentation will discuss the different SBRT modalities available at the Ottawa Hospital Cancer Center. Preliminary work and results towards the development of a simulation tool to compare the dosimetric accuracy of these treatment modalities for spine SBRT will be presented.
Rolf Clackdoyle (Université Grenoble Alpes)
Estimation of Radiotherapy Dose Fields from a Few Projections. How Many?
Multi-leaf collimators (MLCs) play an essential role in radiotherapy by shaping the treatment beam to the target tumour. The MLC consists of opposing pairs of rectangular ‘leaves’ whose role is to allow the beam to pass through a small rectangular region. The leaves can be slid along their long axis and fixed in the desired position for treatment. Typically, there are about 100 pairs of leaves. There are various methods of quality assurance, to verify that the delivered dose matches what was intended. A novel technique of measuring the dose field in real time is being developed in Lyon, using six layers of scintillating fibers with each layer providing a parallel projection of the beam cross-section at different angles. Ignoring the effect of beam penumba and other (smaller) confounding effects, these 6 measurement functions are parallel projections of a constant dose function inside the shape defined by the collimator leaves. The objective is to determine (verify) the dose field, i.e., the dose intensity and the pattern of the collimator leaves. Here, we consider this binary image reconstruction problem, and ask whether the six projections provide enough information to unambiguously determine the dose field.