High resolution small‐scale inorganic scintillator detector: HDR brachytherapy application

Abstract

Purpose: Brachytherapy (BT) deals with high gradient internal dose irradiation made up of a complex system where the source is placed nearby the tumor to destroy cancerous cells. A primary concern of clinical safety in BT is quality assurance to ensure the best matches between the delivered and prescribed doses targeting small volume tumors and sparing surrounding healthy tissues. Hence, the purpose of this study is to evaluate the performance of a point size inorganic scintillator detector (ISD) in terms of high dose rate brachytherapy (HDR-BT) treatment. Methods: A prototype of the dose verification system has been developed based on scintillating dosimetry to measure a high dose rate while using an 192 Ir BT source. The associated dose rate is measured in photons/s employing a highly sensitive photon counter (design data: 20 photons/s). Dose measurement was performed as a function of source-to-detector distance according to TG43U1 recommendations. Overall measurements were carried out inside water phantoms keeping the ISD along the BT needle; a minimum of 0.1 cm distance was maintained between each measurement point. The planned dwell times were measured accurately from the difference of two adjacent times of transit. The ISD system performances were also evaluated in terms of dose linearity, energy dependency, scintillation stability, signal-to-noise ratio (SNR), and signal-to-background ratio (SBR). Finally, a comparison was presented between the ISD measurements and results obtained from TG43 reference dataset. Results: The detection efficiency of the ISD was verified by measuring the planned dwell times at different dwell positions. Measurements demonstrated that the ISD has a perfectly linear behavior with dose rate (R 2 = 1) and shows high SNR (>35) and SBR (>36) values even at the lowest dose rate investigated at around 10 cm from the source. Standard deviation (1σ) remains within 0.03% of signal magnitude, and less than 0.01% STEM signal was monitored at 0.1 cm source-to-detector distance. Stability of 0.54% is achieved, and afterglow stays less than 1% of the total signal in all the irradiations. Excellent symmetrical behavior of the dose rate regarding source position was observed at different radiation planes. Finally, a comparison with TG-43 reference dataset shows that corrected measurements agreed with simulation data within 1.2% and 1.3%, and valid for the source-to-detector distance greater than 0.25 cm. Conclusion:The proposed ISD in this study anticipated that the system could be promoted to validate with further clinical investigations. It allows an appropriate dose verification with dwell time estimation during source tracking and suitable dose measurement with a high spatial resolution both nearby (high dose gradient) and far (low dose gradient) from the source position.

In Vivo Verification of Treatment Source Dwell Times in Brachytherapy of Postoperative Endometrial Carcinoma: A Feasibility Study

“…This calibration distance is larger than the separation of the detector from the source in the patient measurements, ensuring that the SNR in these cases is much higher than the values reported in the SNR section. Although Debnath et al reported a higher SNR for their inorganic scintillator detector, the energy dependence of this type of detector is an important disadvantage in comparison with the PSD in the present study [ 27 ].…”

“…Despite these differences of the individual dwell positions, it is important to note that the maximum total treatment time difference was below 0.3% in all the patients measured. The average accuracy reported by Debnath et al was 0.09%, while the percent deviation of all the measured dwell times in this work was below 0.01% [ 27 ].…”

“…The excellent repeatability behaviour of the PRO-DOSE will be an advantage in future in vivo measurements in intracavitary (IC)–interstitial (IS) cervical cancer treatments because considerably smaller dwell times are used in the active positions of needles, and the transit and interdwell contributions are considerable [ 26 ]. Debnath et al reported results for the repeatability test using their inorganic scintillator detector with a variation lower than 0.35% in all measurements, with a maximum deviation of 0.54% [ 27 ]. The detector response reported by Jorgensen et al across 11 irradiations conducted for the short-term stability test was 0.6% [ 28 ].…”

Development of Experimental Brachytherapy Dosimetry Using Monte Carlo Simulations for Detector Characterization

“…That is, when the ratios ofD det and D wat are taken at a given position (r 0 , θ), the source anisotropy effect does not cancel out. As a result, the absorbed-dose energy dependence correction factor can have multiple values at the same radial distance r. The findings demonstrate that a single absorbed-dose energy correction function is not sufficient for high-Z detectors although it is adopted in some experimental studies (e.g., Ruiz-Arrebola et al 2020, Debnath et al 2021).…”

“…(Kertzscher and Beddar 2019, Linares Rosales et al 2020b, Debnath et al 2021, Jørgensen et al 2021a.…”