Monte Carlo simulation study of an in vivo four-dimensional tracking system with a diverging collimator for monitoring radiation source (Ir-192) location during brachytherapy: proof of concept and feasibility

Introduction: The aim of this study was to demonstrate the potential of an in vivo four-dimensional (4D) tracking system to accurately localize the radiation source, Iridium-192 (Ir-192) in high-dose rate brachytherapy. Methods: To achieve time-dependent 3D positioning of the Ir-192 source, we devised a 4D tracking system employing multiple compact detectors. During the system's design phase, we conducted comprehensive optimization and analytical evaluations of the diverging collimator employed for detection purposes. Subsequently, we executed 3D reconstruction and positioning procedures based on the 2D images obtained by six detectors, each equipped with an optimized diverging collimator. All simulations for designing and evaluating the 4D tracking system were performed using the open-source GATE (v9.1) Monte Carlo platform based on the GEANT4 (v10.7) toolkit. In addition, to evaluate the accuracy of the proposed 4D tracking system, we conducted simulations and 3D positioning using a solid phantom and patient data. Finally, the error between the reconstructed position coordinates determined by the tracking system and the original coordinates of the Ir-192 radiation source was analyzed. Results: The parameters for the optimized diverging collimator were a septal thickness of 0.3 mm and a collimator height of 30 mm. A tracking system comprising 6 compact detectors was designed and implemented utilizing this collimator. Analysis of the accuracy of the proposed Ir-192 source tracking system found that the average of the absolute values of the error between the 3D reconstructed and original positions for the simulation with the solid phantom were 0.440 mm for the x coordinate, 0.423 mm for the y coordinate, and 0.764 mm for the z coordinate, and the average Euclidean distance was 1.146 mm. Finally, in a simulation based on data from a patient who underwent brachytherapy, the average Euclidean distance between the original and reconstructed source position was 0.586 mm. Discussion: These results indicated that the newly designed in vivo 4D tracking system for monitoring the Ir-192 source during brachytherapy could determine the 3D position of the radiation source in real time during treatment. We conclude that the proposed positioning system has the potential to make brachytherapy more accurate and reliable.

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

Objective. Precise monitoring of the position and dwell time of iridium-192 (Ir-192) during high-dose-rate (HDR) brachytherapy is crucial to avoid serious damage to normal tissues. Source imaging using a compact gamma camera is a potential approach for monitoring. However, images from the gamma camera are affected by blurring and statistical noise, which impact the accuracy of source position monitoring. This study aimed to develop a deep-learning approach for estimating ideal source images that reduce the effect of blurring and statistical noise from experimental images captured using a compact gamma camera.Approach. A double pix2pix model was trained using the simulated gamma camera images of an Ir-192 source. The first model was responsible for denoising the Ir-192 images, whereas the second model performed super resolution. Trained models were then applied to the experimental images to estimate the ideal images.Main results. At a distance of 100 mm between the compact gamma camera and the Ir-192 source, the difference in full width at half maximum (FWHM) between the estimated and actual source sizes was approximately 0.5 mm for a measurement time of 1.5 s. This difference has been improved from approximately 2.7 mm without the use of DL. Even with a measurement time of 0.1 s, the ideal images could be estimated as accurately as in the 1.5 s measurements. This method consistently achieved accurate estimations of the source images at any position within the field of view; however, the difference increased with the distance between the Ir-192 source and the compact gamma camera.Significance. The proposed method successfully provided estimated images from the experimental images within errors smaller than 0.5 mm at 100 mm. This method is promising for reducing blurring and statistical noise from the experimental images, enabling precise real-time monitoring of Ir-192 sources during HDR brachytherapy.

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

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.

High dose rate192Ir versus high dose rate60Co brachytherapy: an overview of systematic reviews of clinical responses of gynecological cancers from 1984 to 2020

The Purpose. Radioisotope of192Iradium (192Ir) has a half-life (74 days) and is not easily accessible in developing countries. As a result, by the time source shipment clearance and the customs paperwork are completed, a large proportion of useful activity had already been decayed away. In fact,60Cobalt (60Co) remote afterloading systems are commercially available by many venders. As a result, it may well become an alternative source to192Ir and conform many of these challenges. The aim of this study is that to report clinical responses of different types of gynaecological cancers treated with high dose rate (HDR)192Ir and HDR60Co brachytherapy in order to check whether HDR60Co could be used as an alternative brachytherapy, source to HDR192Ir.Materials and Methods. A retrospective study of clinical responses of different types of gynaecological cancers, staged from I to IV according to recommendations of International Federation of Gynaecology and Obstetrics (FIGO), treated by brachytherapy alone, radiotherapy alone (combined brachytherapy and radiotherapy) and combined radiotherapy and chemotherapy (brachytherapy, radiotherapy and chemotherapy) between 1984 and December 2020 was conducted. The patients were treated with external beam radiotherapy 45-51 Gy boosted with HDR192Ir and HDR60Co afterloading brachytherapy of 18-30 Gy to point A.The results. The study scrutinized the data of 11086 patients with different types of gynaecological cancers. Most of the patients, 70 percent of them, were diagnosed with gynaecological cancers in stages II and III. For patients treated with192Ir brachytherapy source 5-years overall survival rate (OS), local control, 2-years, 5-years and 10-years disease free survival (DFS), complications of gastro-intestine (GI) and complications of genito-urinary (GU) were 63.5%, 92%, 72.6%, 64.07%, 43.75%, 3.9% and 5.92%, but for those treated with60Co they were 57.7%, 86.63%, 82.5%, 53.35%, 43.75%, 4.8% and 3.7%, respectively.Conclusions.The use of HDR60Co brachytherapy has the capacity to produce overall survival rate and disease control in patients with carcinoma of the gynaecology comparable to that reported for HDR192Ir brachytherapy. Currently, the toxicity and damage of the normal tissues and radiation-related second cancers are of a similar incidence to that of standard HDR192Ir brachytherapy. Source exchange frequency is not a serious concern because it requires less frequency of replacement, and commissioning can be accomplished within years; hence, replacing HDR192Ir with HDR60Co brachytherapy achieves significant cost saving. Therefore, we recommend that60Co source ought to be the first choice for low resource radiotherapy setting as it offers economic advantages over192Ir and have comparable clinical outcomes to that of192Ir source.