Source position measurement by Cherenkov emission imaging from applicators for high‐dose‐rate brachytherapy

Abstract

Purpose We developed a novel and simple method to measure the source positions in applicators directly for high‐dose‐rate (HDR) brachytherapy based on Cherenkov emission imaging, and evaluated the performance. Methods The light emission from plastic applicators used in cervical cancer treatments, irradiated by an 192Ir γ‐ray source, was captured using a charge‐coupled device camera. Moreover, we attached plastics of different shapes, including tapes, tubes, and plates to a metal applicator, to use as screens for the Cherenkov imaging. We determined the source positions and dwell intervals from the light profiles along with the applicator and compared these with preset values and dummy marker measurements. Results The source positions and dwell intervals measured from the light images were comparable to the dummy marker measurements and preset values. The distance from the applicator tip to the first source positions agreed with the dummy marker measurements within 0.2 mm for the plastic tandem. The dwell intervals measured using the Cherenkov method agreed with the preset values within 0.6 mm. The distances measured with three plastic types on the metal applicator also agreed with the dummy marker measurements within 0.2 mm. The dwell intervals measured using the plastic tape agreed with the preset values within 0.7 mm. Conclusions The proposed method should be suitable for rapid and easy quality assurance (QA) investigations in HDR brachytherapy, as it enables source position using a single image. The method allows for real‐time, filmless measurements of the source positions to be obtained and is useful for rapid feedback in QA procedures.

Real-time tracking of source movement by Cherenkov emission imaging for high-dose-rate brachytherapy

“…The method enables the measurement of the source position, source strength, and dose distribution using a single image without corrections, and thus, it should be suitable for rapid and easy QA verification in the HDR brachytherapy. Furthermore, we proposed the use of plastics, in the form of either a plastic applicator itself or plastic attached to a metal applicator, as a "screen" that visualizes the invisible radiation as visible Cherenkov light for the direct measurement of source positions, for commissioning and QA in the HDR brachytherapy [31].…”

“…The Cherenkov light that was induced by the irradiation of water with an 192 Ir source was reflected by a mirror and recorded by the high-sensitivity camera at 30 frames per second (fps). We mounted an image intensifier (VS4-1845, VideoScope, VA, U.S.A.) [32] in front of a CCD camera (BU-60M, BITRAN CORPORATION, Gyoda, Japan) to capture an image of Cherenkov light emission that was much brighter (approximately a few hundred times) than that when our previous tool was used [30,31]. The camera was placed 50.5 cm from the water tank and perpendicular to the source axis.…”

“…The source positions were determined in two manners: 1) the intensity centroids and 2) the midpoint of the brightness profiles [13,30,31]. The time course of the source positions was obtained from a source tracking movie using the ImageJ software (ver.…”

“…The source positions were characterized at the midpoint of the full width at half maximum (FWHM) in the profiles along the applicator axis [13,30,31]. We compared the intervals that were measured from the Cherenkov light images to those of the preset values.…”

“…The source positions derived from the time course (intensity centroids) are summarized in table 2 for different source positions (points 1 to 3). The source positions were defined as the midpoints of the emission profiles, as proposed by the authors in previous studies [13,30,31]. The distances from the upper edge in the image were indicated to compare the two analyses methods (intensity centroids and midpoint).…”