DIRECT READING MEASUREMENT OF ABSORBED DOSE WITH PLASTIC SCINTILLATORS - THE GENERAL CONCEPT AND APPLICATIONS TO OPHTHALMIC PLAQUE DOSIMETRY

We have developed dosemeters based on plastic scintillators for a vari ety of applications in radiation therapy. The dosemeters consist basic ally of a tissue-substituting scintillator probe, an optical fiber lig ht guide, and a photomultiplier tube. The background light generated i n the light guide can be compensated by a simultaneous measurement of the light from a blind fiber. Plastic scintillator dosemeters combine several advantageous properties which render them superior to other do semeter types for many applications: minimal disturbance of the radiat ion field because of the homogeneous detector volume and the approxima te water equivalence; no dependence on temperature and pressure (under standard clinical conditions) and angle of radiation incidence; no hi gh voltage in the probe; high spatial resolution due to small detector volumes; direct reading of absorbed doses; and a large dynamical rang e. The high spatial resolution together with direct reading make these detectors suitable for real-time 3-D dosimetry using multi-channel de tector systems. Such a system has been developed for eye plaque dosime try and successfully employed for dosimetric treatment optimization. T he plaque optimization can be performed by dosimetric measurements for the individual patient (''dosimetric treatment planning''). The time consumption for this procedure is less than for a physically correct c omputer-based therapy planning, e.g., by means of a Monte Carlo simula tion. (C) 1996 American Association of Physicists in Medicine.