Sci‐PM Sat ‐ 03: Conformal dose verification using cone beam optical computed tomography and polymer gel dosimeters: A feasibility study

Abstract

The advent of image guided radiotherapy, particularly with intensity modulation techniques, offers the potential to improve patient outcomes by conforming the dose to a tumour thereby decreasing irradiation of surrounding tissues. This potentially reduces complication rates and enables dose escalation. However, intensity modulated radiation therapy necessarily requires far greater complexity in treatment planning and dose delivery and, ideally, delivery must be verified directly in three‐dimensions to ensure that the planning objectives are achieved. Currently no convenient system exists for such 3D dosimetry. In this work we provide an initial assessment of a modality that could provide exactly this functionality using polymer gel dosimeters that polymerize when exposed to radiation. Two dosimeters based on polyacrylamide gelatin (PAG) and on a new formulation using N‐vinylFormamide are investigated. The dosimeters are prepared with Tetrakis to enable preparation in conventional fumehoods in an oxygen environment. A novel cone beam optical CT unit designed in London Ontario specifically for gel dosimetry provides dose measurements. The radiation induced polymerization, and hence dose, affects light attenuation and, hence CT numbers in optical CT, since the polymers act as scattering centres for light. We will show that apart from an initial threshold region, the relationship between dose and optical CT numbers is linear over the range investigated. An example of the visualization of a treatment failure will be illustrated. Though preliminary, these results suggest that cone beam optical CT polymer gel dosimetry could provide an efficient and economical method for 3D dose delivery verification.