Characterization of spectral and intensity changes with measurement geometry in various light guides used in scintillation dosimetry

Abstract

The insignificant change in the CLR with delivered dose indicates that a single CLR value over the investigated dose range is sufficient for accurate Čerenkov subtraction. Variations in the stem-effect spectrum shape can occur with changes in irradiation geometry. The magnitude of the changes are governed by the fiber construction and the optical properties of the fiber. The observed spectral shape changes can be explained by a combination of variations in optical path length through the fiber and the fiber fluorescent signal contribution to the stem-effect. These spectral shape variations directly influence the calculated CLR values. This work confirms that careful characterization of scintillation detectors is important as changes in the stem-effect spectrum can cause changes in the CLR. If the CLR changes between the reference and measurement conditions, this could result in an incorrect stem-effect subtraction and reduced measurement accuracy.

Real‐time in vivo dosimetry system based on an optical fiber‐coupled microsized photostimulable phosphor for stereotactic body radiation therapy

“…This approach is very effective if the measurements fall within these ranges of the calibration conditions 29,48–50 . However, it has been reported that the calibration conditions affect the accuracy of stem signal elimination 30,32 . Furthermore, the spectrum during measurement may differ from that at the time of calibration depending on the bending of the optical fiber 32 and temperature, and these factors may also cause errors.…”

“…29,[48][49][50] However, it has been reported that the calibration conditions affect the accuracy of stem signal elimination. 30,32 Furthermore, the spectrum during measurement may differ from that at the time of calibration depending on the bending of the optical fiber 32 and temperature, and these factors may also cause errors. Guillot et al 30 noted that optical fiber attenuation could be an additional source of error.…”

“…Even in the spectral, or chromatic, method [27][28][29][30][31] that is considered to be preferable, the measurement precision may deteriorate depending on the conditions of the calibration performed in advance. 30,32 In particular, when the sensitive volume of the scintillator is small, the ratio of the stem signal to the scintillator signal increases, so correction may be difficult. Furthermore, since the luminous efficiencies of most plastic scintillators with respect to radiation are low, 33 if the sensitive volume is reduced, the signal is significantly reduced.…”

“…Various countermeasures 21–26 against stem signals have been developed, but the effects of these signals cannot be completely eliminated. Even in the spectral, or chromatic, method 27–31 that is considered to be preferable, the measurement precision may deteriorate depending on the conditions of the calibration performed in advance 30,32 . In particular, when the sensitive volume of the scintillator is small, the ratio of the stem signal to the scintillator signal increases, so correction may be difficult.…”

Monte Carlo modeling of the influence of strong magnetic fields on the stem‐effect in plastic scintillation detectors used in radiotherapy dosimetry

“…The main caveat of these detectors, as many have previously highlighted, 1,3–5,8–12 is that they are susceptible to an unwanted background, or stem‐effect, signal that can degrade the accuracy of these detectors if it is not properly removed. The stem‐effect is composed of Čerenkov radiation generated in the light guide and sensitive detector volume and fluorescence generated in the light guide.…”