Characterization of a tissue equivalent plastic scintillator dosimetry system

High precision techniques in radiation therapy such as IMRT offer the potential for improved target coverage and increased normal tissue sparing. The complex fluence maps used in many of these techniques, however, lead to more challenging quality assurance with dose verification being labor‐intensive and time consuming. We have developed a dose verification system using tissue equivalent plastic scintillator that provides easy to acquire, rapid electronic and directly digital dose measurements in a plane perpendicular to the beam. The prototype system consists of a water‐filled Lucite phantom with a scintillator screen built into the top surface. The phantom contains a plastic mirror to reflect scintillation light towards a viewing window where it is captured using a CCD camera and a personal computer. Optical photon spread is removed using a micro‐louvre optical collimator and by deconvolving a glare kernel from the raw images. System characterization tests indicate excellent dose and spatial linearity. The system was found to have good signal uniformity and to be independent of dose rate. Spatial resolution was determined to be 0.53 mm/pixel. The system's ability to verify a dynamic treatment field was evaluated using a 60° enhanced dynamic wedge and comparing the results to 2‐D film dosimetry. Results indicate agreement within 5% of 2‐D film dosimetry. With further development this system promises to provide a fast, directly digital, and tissue equivalent alternative to current dose verification systems. © 2005, American Association of Physicists in Medicine. All rights reserved.