Inorganic scintillation detectors for Ir brachytherapy.

Many brachytherapy (BT) errors could be detected with real-time in vivo dosimetry technology. Inorganic scintillation detectors (ISDs) have demonstrated promising capabilities for BT, because some ISD materials can generate scintillation signals large enough that (a) the background signal emitted in the fiber-optic cable (stem signal) is insignificant, and (b) small detector volumes can be used to avoid volume averaging effects in steep dose gradients near BT sources. We investigated the characteristics of five ISD materials to identify one that is appropriate for BT. ISDs consisting of a 0.26 to 1.0 mm volume of ruby (AlO:Cr), a mixture of YO:Eu and YVO:Eu, ZnSe:O, or CsI:Tl coupled to a fiber-optic cable were irradiated in a water-equivalent phantom using a high-dose-rate Ir BT source. Detectors based on plastic scintillators BCF-12 and BCF-60 (0.8 mm volume) were used as a reference. Measurements demonstrated that the ruby, YO:Eu+YVO:Eu, ZnSe:O, and CsI:Tl ISDs emitted scintillation signals that were up to 19, 19, 250, and 880 times greater, respectively, than that of the BCF-12 detector. While the total signals of the plastic scintillation detectors were dominated by the stem signal for source positions 0.5 cm from the fiber-optic cable and  >3.5 cm from the scintillator volume, the stem signal for the ruby and YO:Eu+YVO:Eu ISDs were  <1% of the total signal for source positions  <3.4 and  <4.4 cm from the scintillator, respectively, and  <0.7% and  <0.5% for the ZnSe:O and CsI:Tl ISDs, respectively, for positions  ⩽8.0 cm. In contrast to the other ISDs, the YO:Eu+YVO:Eu ISD exhibited unstable scintillation and significant afterglow. All ISDs exhibited significant energy dependence, i.e. their dose response to distance-dependent Ir energy spectra differed significantly from the absorbed dose in water. Provided that energy dependence is accounted for, ZnSe:O ISDs are promising for use in error detection and patient safety monitoring during BT.