RADIATION-DOSE DISTRIBUTIONS IN 3 DIMENSIONS FROM TOMOGRAPHIC OPTICAL-DENSITY SCANNING OF POLYMER GELS .1. DEVELOPMENT OF AN OPTICAL SCANNER

A new method of dosimetry of ionizing radiations has been developed th at makes use of tissue-equivalent polymer gels which are capable of re cording three-dimensional dose distributions. The dosimetric data stor ed within the gels are measured using optical tomographic densitometry . The dose-response mechanism relies on the production of light scatte ring microparticles which result from the polymerization of acrylic co monomers dispersed in the gel. The attenuation of a collimated Light b eam caused by scattering in the irradiated optically turbid medium is directly related to the radiation dose over the range 0-10 Gy. An opti cal scanner has been developed which incorporates an He-Ne laser, phot odiode detectors, and a rotating gel platform. Using mirrors mounted o n a translating stage, the laser beam scans across the gel between eac h incremental rotation of the platform. Using the set of optical densi ty projections obtained, a cross sectional image of the radiation fiel d is then reconstructed. Doses in the range 0-10 Gy can be measured to better than 5% accuracy with a spatial resolution approximate to 2 mm using the current prototype scanner. This method can be used for the determination of three-dimensional dose distributions in irradiated ge ls, including measurements of the complex distributions produced by mu lti-leaf collimators, dynamic wedge and stereotactic treatments, and f or quality assurance procedures.