Abstract
In high-dose-rate (HDR) brachytherapy, verification of the
Ir-192 source's position during treatment is needed because such a
source is extremely radioactive. One of the methods used to measure
the source position is based on imaging the gamma rays from the
source, but the absolute position in a patient cannot be
confirmed. To confirm the absolute position, it is necessary to
acquire an optical image in addition to the gamma ray image at the
same time as well as the same position. To simultaneously image the
gamma ray and optical images, we developed an imaging system
composed of a low-sensitivity, high-resolution gamma camera
integrated with a CMOS camera. The gamma camera has a 1-mm-thick
cerium-doped yttrium aluminum perovskite (YAIO3: YAP(Ce))
scintillator plate optically coupled to a position-sensitive
photomultiplier (PSPMT), and a 0.1-mm-diameter pinhole collimator
was mounted in front of the camera to improve spatial resolution and
reduce sensitivity. We employed the concept of a periscope by
placing two mirrors tilted at 45 degrees facing each other in front
of the gamma camera to image the same field of view (FOV) for the
gamma camera and the CMOS camera. The spatial resolution of the
imaging system without the mirrors at 100 mm from the Ir-192 source
was 3.2 mm FWHM, and the sensitivity was 0.283 cps/MBq. There was
almost no performance degradation observed when the mirrors were
positioned in front of the gamma camera. The developed system could
measure the Ir-192 source positions in optical and gamma ray
images. We conclude that the developed imaging system has the
potential to measure the absolute position of an Ir-192 source in
real-time clinical measurements.
The Absolute Measurement of the Intensity of Sound
