Technical note: Short‐time sequential high‐energy gamma photon imaging using list‐mode data acquisition system for high‐dose‐rate brachytherapy

Abstract

Purpose Measurement of the dwell time and moving speed of a high‐activity iridium‐192 (Ir‐192) source used for high‐dose‐rate (HDR) brachytherapy is important for estimating the precise dose delivery to a tumor. For this purpose, we used a cerium‐doped yttrium aluminum perovskite (YA1O3:YAP(Ce)) gamma camera system, combined with a list‐mode data acquisition system that can acquire short‐time sequential images, and measured the dwell times and moving speeds of the Ir‐192 source. Methods Gamma photon imaging was conducted using the gamma camera in list mode for the Ir‐192 source of HDR brachytherapy with fixed dwell times and positions. The acquired list‐mode images were sorted to millisecond‐order interval time sequential images to evaluate the dwell time at each position. Time count rate curves were derived to calculate the dwell time at each source position and moving speed of the source. Results We could measure the millisecond‐order time sequential images for the Ir‐192 source. The measured times for the preset dwell times of 2 s and 10 s were 1.98 to 2.00 s full width at half maximum (FWHM) and 10.0 s FWHM, respectively. The dwell times at the first dwell position were larger than those at other positions. We also measured the moving speeds of the source after the dwells while moving back to the afterloader and found the speed increased with the distance from the edge of the field of view to the last dwell position. Conclusion We conclude that millisecond‐order time sequential imaging of the Ir‐192 source is possible by using a gamma camera and is useful for evaluating the dwell times and moving speeds of the Ir‐192 source.

Estimating blurless and noise-free Ir-192 source images from gamma camera images for high-dose-rate brachytherapy using a deep-learning approach

“…Calibration measurement of Ir-192 images using previously developed compact gamma camera The images used in this study were acquired from an Ir-192 source specifically designed for HDR brachytherapy. These images were captured using a compact gamma camera developed in a previous study [16]. The imaging detector of the compact gamma camera consists of a cerium-doped yttrium aluminum perovskite (YA1O 3 :YAP(Ce)) scintillator and an 8 × 8 array of multi-anode flat panel photomultiplier tube (FP-PMT).…”

“…Figure 1 shows a schematic diagram of the compact gamma camera. The camera specifications have been comprehensively described in previous research reports [16].…”

“…Several attempts have been made to image and monitor the position of the Ir-192 source, as documented in various trials reported in the literature [5][6][7][8][9][10][11][12][13]. As part of this effort, a compact gamma camera fitted with a pinhole collimator was developed [14][15][16], successfully acquiring short-term sequential images that showed the movement of the Ir-192 source [16]. At a distance of 100 mm from the camera collimator surface, the pinhole camera exhibited a spatial resolution of approximately 3.0 mm full width at half maximum (FWHM).…”

“…However, as the distance between the camera and the Ir-192 source increased, the spatial resolution deteriorated. Moreover, images acquired with short-time intervals suffered from significant statistical noise [16]. To achieve more precise monitoring of the Ir-192 source position, source images with reduced blurring and statistical noise are highly desirable.…”

“…Moreover, if we can generate images with a significant reduction in blurring and statistical noise fluctuation, it might be possible to calculate the dose delivered to the tumor and surrounding tissue based on radioactivity and the size and exact location of the source relative to the tumor. In this study, we employ a deep-learning (DL) approach to provide an accurate estimation of the size and location of the Ir-192 source from experimental images obtained from a compact gamma camera developed in a previous study [16].…”