A brachytherapy
treatment was simulated in a water phantom while real-time IVD was performed
(phantom size: 25x30x30 cm3, water temperature: 37.5±1oC). A ZnSe:O-based scintillation detector [1] with an
in-house developed treatment verification software was used for IVD, and the
procedure resembled a clinical routine. Prior to irradiation, a calibration of
the scintillator was performed in a plastic phantom. For the simulated
treatment, six needles were used for irradiation and the dosimeter was placed in
a dedicated needle (distances to the other needles, 1, 1, 2, 2, 3 and 4 cm). A
treatment plan (exported from Oncentra Prostate) was loaded into the treatment
verification software to generate the expected dose rates, fig. 1. The
treatment plan consisted of 5-12 dwell positions in each needle with dwell
times in the range of 0.7-2 s.
During irradiation, the
software recorded and converted the signal into dose rate including a
correction of the energy-dependency based on the signal height. A graphical
user interface provided a direct comparison of the measured and expected dose
rates every 50 ms, fig. 1. After the irradiation of each needle, an IVD-based
source tracking methodology was used to determine the position of the needle. The
discrepancy between expected and tracked position of the given needle was displayed.
The irradiation was
repeated ten times while the treatment verification software was giving
real-time feedback. Furthermore, two irradiations with induced errors were
performed: A swap of guide tubes for channel 5 and 6, and a 5 mm radial shift
of channel 3.