| Summary: | Radiation therapy treatment of cancer is increasingly concerned with delivering dose
distributions that conform to the tumour volume. For verification of treatment planning
computer dose calculations, these conformal therapies demand an accurate, sensitive, high
resolution three dimensional (3D) dosimeter. Polymer gels are novel, inherently 3D, tissue
equivalent radiation dosimeters. Traditionally, dose distributions recorded in polymer gel are
read out using magnetic resonance imaging (MRI). Presented here is a feasibility study on a
new 3D dosimetry technique that uses x-ray computed tomography (CT) to read dosimetric
information from polymer gels. The technique exploits a gel density change that occurs in
response to ionizing radiation. This study has three main goals: 1) to develop a protocol for
producing quality CT polymer gel images; 2) to evaluate the nature and reproducibility of the
dosimeter's CT number (JVcr)-dose response; and 3) to compare this technique with MRI
polymer gel dosimetry. A quantitative discussion of the density changes occurring in the gel
in response to ionization radiation is also provided. Experiments are conducted using a PAG
(polyacrylamide and gelatin) gel dosimeter irradiated with four intersecting 10 M V photon
beams. The NCT -dose response is found to be linear and reproducible over the range of 200
to 1OOOcGy. At room temperature the response is (8.7 ± 0.3)xl0⁻³ NCT/cGy resulting in a
limited dose resolution, - 100 cGy. Gel temperature during imaging is determined to have
only a small effect, 0.3%/°C, on the dose response. Spatial resolution is 0.5 mm in the image
plane and 10mm-1mm (depending on noise requirements) in the third dimension. Despite
the low dose resolution, preliminary results indicate this technique provides accurate
localization of high dose regions and, given the availability and speed of CT imaging, has the
potential to be a valuable and practical tool for radiation therapy clinics. === Science, Faculty of === Physics and Astronomy, Department of === Graduate
|
|---|
