High‐dose rate intracavitary brachytherapy pretreatment dwell position verification using a transparent applicator

Abstract

PurposeThe major errors in HDR brachytherapy are related to treatment distance, almost all of which are caused by incorrect applicator information. The aim of this study is to propose a quick pretreatment verification method to evaluate channel length and dwell position with a transparent applicator, which, in addition, is suitable as an education tool to assist in the understanding of the applicator structure.MethodsA transparent applicator model was fabricated using a three‐dimensional printer and transparent resin. Its aim is to be a replica of a real gynecological applicator. The pretreatment verification is performed by observing the planned dwell positions of a check cable inside a transparent applicator. A digital camera acquired images and the dwell positions of the radioactive source and check cable were evaluated by comparing them with respect to the theoretical dwell positions marked by the proper x‐ray marker. The potential effectiveness of verification using a transparent applicator was also evaluated using brachytherapy events reported in the literature.ResultsThe transparent applicator closely resembles the real applicator in shape and had an error of less than 0.2 mm. The average dwell position displacement between the radioactive source and check cable was 0.4 mm. The analysis of brachytherapy events showed that channel‐length, dwell‐position, and step‐size errors made up 50% of all events, but affected 64% of all patients.ConclusionsThe transparent applicator model enables a noninvasive, repeatable verification of the channel length and dwell positions to be performed before treatment. This verification has the potential to help prevent common errors in treatment delivery. In addition, the transparent applicator model can be used as a teaching tool to help clinicians understand the operation of the applicator, lowering the risk of events.

First experience of 192Ir source stuck event during high-dose-rate brachytherapy in Japan

“…According to reports from the US NRC and ICRP 97 and the Japanese user community, many of the reported events were related to inappropriate channel length, incorrect residence location, incorrect step size, and incorrect prescription volume. Most causes of these events were human errors that were related to treatment planning or commissioning [1,5,10]. Few reports Reports also revealed the incidence of all brachytherapy events to be 0.02-1.6% [6,8,9].…”

“…The cause of this accident was that the input channel length was continuously incorrect; the treatment was performed 3 cm off the tip of the ovoid applicator tip. In Japan, 9 HDR brachytherapy-related events occurred between March 2008 and March 2017 (reported by a single manufacturer's user community) [10]. Most of those events were classified as occurring because of the wrong dwell position or dwell time of the source.…”

Development of an HDR‐BT QA tool for source position verification

“…To the best of our knowledge, no report has described HDR-BT QA tools having these functions. [11][12][13][14][15][16] Our QA tool allows for verification of actual source positions, as the interaction between Ir-192 gamma ray and radiopaque markers blackens radiographic films (Fig. 2).…”

“…Since errors related to applicator offset cannot be detected by mechanical testing alone (e.g., verification of dummy source positions using radio- Several studies have reported methods for HDR-BT source position verification. [11][12][13][14][15][16][17] Radiochromic dosimetry films have been used to verify active source positions for HDR-BT, 11 although a lack of information on reference positions makes it difficult to quantitatively assess source positions. To address this issue, some have suggested methods to add information on films, such as by superimposing a source autoradiograph on a radiograph of dummy sources inside the applicator, 12 manually marking reference positions, 13 or utilizing a tungsten wire.…”

“…14 Meanwhile, others have reported on methods to obtain source information without using radiographs, for example, with a plastic scintillator block and CCD camera 15 or a transparent applicator. 16 However, none of these methods involved the use of a…”