Online pretreatment verification of high-dose rate brachytherapy using an imaging panel

Abstract

Brachytherapy is employed to treat a wide variety of cancers. However, an accurate treatment verification method is currently not available. This study describes a pre-treatment verification system that uses an imaging panel (IP) to verify important aspects of the treatment plan. A detailed modelling of the IP was only possible with an extensive calibration performed using a robotic arm. Irradiations were performed with a high dose rate (HDR) Ir source within a water phantom. An empirical fit was applied to measure the distance between the source and the detector so 3D Cartesian coordinates of the dwell positions can be obtained using a single panel. The IP acquires 7.14 fps to verify the dwell times, dwell positions and air kerma strength (Sk). A gynecological applicator was used to create a treatment plan that was registered with a CT image of the water phantom used during the experiments for verification purposes. Errors (shifts, exchanged connections and wrong dwell times) were simulated to verify the proposed verification system. Cartesian source positions (panel measurement plane) have a standard deviation of about 0.02 cm. The measured distance between the source and the panel (z-coordinate) have a standard deviation up to 0.16 cm and maximum absolute error of ≈0.6 cm if the signal is close to sensitive limit of the panel. The average response of the panel is very linear with Sk. Therefore, Sk measurements can be performed with relatively small errors. The measured dwell times show a maximum error of 0.2 s which is consistent with the acquisition rate of the panel. All simulated errors were clearly identified by the proposed system. The use of IPs is not common in brachytherapy, however, it provides considerable advantages. It was demonstrated that the IP can accurately measure Sk, dwell times and dwell positions.

HDR brachytherapy in vivo source position verification using a 2D diode array: A Monte Carlo study

“…Source position verification using EPIDs also requires large and expensive systems that have limited availability. This study has shown that similar source position verification accuracy to EPIDs may be achieved with the MP system. Furthermore, the MP system has been shown to have a superior timing resolution of less than 1 ms .…”

“…Real‐time source identification of dwell positions during HDR prostate brachytherapy treatments based on electronic portal imaging devices (EPIDs) have been performed previously . In one study, the authors retrospectively compared the planned vs measured source positions using an EPID embedded into the couch for eight treatment fractions, and the mean linear distance between the planned and measured dwell positions was found to be 1.8 mm (range 0.7–3.9 mm) .…”

Dosimetric performance of a multipoint plastic scintillator dosimeter as a tool for real‐time source tracking in high dose rate Ir brachytherapy

“…Additionally, previous work explored the sourcetracking capacity of different detectors in HDR brachytherapy. [23][24][25][26][27][28] Some studies used an array of dosimeters placed on the patient's skin, and others a flat-panel detector. In a study of source-position tracking with a single-point detector in HDR brachytherapy, Johansen et al 24 used the dose values from the treatment planning system to develop a method to determine average source shifts within catheters.…”

A Monte Carlo study on the feasibility of real-time in vivo source tracking during ultrasound based HDR prostate brachytherapy treatments

“…This poor signal to noise ratio necessitates the use of longer integration times in the detector system and may therefore preclude the system from performing real-time source tracking analysis. This issue has been discussed in previous publications on the use of EPID devices for source tracking [13][14][15][16]. The Magic Plate system, however, is capable of operating with variable integration times between 14 -9900 μs, with a stable sampling frequency between 0.1 -10 kHz.…”

“…Source tracking of dwell positions during HDR pBT treatments based on electronic portal imaging devices (EPIDs) have been performed previously [13][14][15][16]. However, when used for HDR brachytherapy source tracking, these EPID based devices are required to operate using low frame rates due to poor signal to noise ratios, and when compounded with their inherently slow read out electronics, loss of data for short dwell times can occur [14].…”