Direct reading measurement of absorbed dose with plastic scintillators—The general concept and applications to ophthalmic plaque dosimetry

Abstract

We have developed dosemeters based on plastic scintillators for a variety of applications in radiation therapy. The dosemeters consist basically of a tissue-substituting scintillator probe, an optical fiber light guide, and a photomultiplier tube. The background light generated in 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 dosemeter types for many applications: minimal disturbance of the radiation field because of the homogeneous detector volume and the approximate water equivalence; no dependence on temperature and pressure (under standard clinical conditions) and angle of radiation incidence; no high voltage in the probe; high spatial resolution due to small detector volumes; direct reading of absorbed doses; and a large dynamical range. The high spatial resolution together with direct reading make these detectors suitable for real-time 3-D dosimetry using multi-channel detector systems. Such a system has been developed for eye plaque dosimetry and successfully employed for dosimetric treatment optimization. The 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 computer-based therapy planning, e.g., by means of a Monte Carlo simulation.

NCS Report 14: Quality control of sealed beta sources in brachytherapy

“…Measurements on ophthalmic applicators ( 125 I and 106 Ru/ 106 Rh) showed a contribution of Cherenkov light of no more than 2%. This system has been used for measurements on both ophthalmic plaques [59] and intravascular brachytherapy sources [60][61][62]. The Optidos TM is a commercial version of this system developed by PTW (PTW Freiburg GmbH, Freiburg, Germany).…”

Rare Earth Doped Silica Optical Fibre Sensors for Dosimetry in Medical and Technical Applications

“…As examples, de Boer and colleagues [6] performed spectral measurement of radiation-induced light in plastic scintillator dosimeters and investigated the feasibility of optical filtering for the stem effect subtraction. Flühs and colleagues [7] developed dosimeters based on plastic scintillators for a variety of applications in radiation therapy and, in particular, employed such systems for eye plaque dosimetric treatment optimization. Létourneau and colleagues [8] studied the properties of a miniature scintillating detector, suitable for small field radiation dosimetry, using a configuration similar to that of Beddar [4] for facing the limitation due to the stem effect.…”

Photon dosimetry using plastic scintillators in pulsed radiation fields

“…This is the primary reason why plastic scintillators have been so extensively studied for use as in-situ real-time dosimetry probes for high-energy bremsstrahlung medical radiation treatment monitoring. 1,[6][7][8][9][10] Medical dosimetry research has shown common plastic scintillators to have water equivalent (tissue equivalent) energy deposition properties from 0.2 to 20 MeV, with the ratio of dose deposited in plastic to that deposited in water Dose Scintillator /Dose Water of about 0.98. 3,4,11,12 It is worth noting that most of the work cited here has involved placing small scintillators ( <1 cm 2 ) within the body or a water-equivalent phantom, therefore establishing a charge particle equilibrium (CPE) condition that satisfies the Bragg-Gray principle.…”