Multi-mode Real-time Image Guided Brachytherapy For Cervical Carcinoma

PurposeBrachytherapy is an integral part of radiotherapy treatment for locally advanced cervical cancer.The traditional brachytherapy used the template standard treatment.The evaluation of dose is not accurate.The injury of rectum or bladder is common,even serious complication such as fistula,which affects the life quality of patients,the treatment and prognosis of primary disease.With the rapid development of medical imaging,three-dimensional(3D)conformal radiotherapy technique based on soft tissue imaging has been gradually applied in brachytherapy for precise and individualized treatment of cervical cancer.But the single image technology has many problems,such as complex process,repeated inspection,and high price.The purpose of this study was to develop a new real-time image guided system.Based on the real-time registration technology of ultrasound(US)and CT/MR image,we set up a real-time imaging guided brachytherapy system for cervical cancer with a combined intracavitary/interstitial(IC/IS)applicator by 3D printing technique.The registration between real-time three-dimensional US images and pre-treatment CT/MR diagnostic images was developed to reflect the changes of tumor location and size for accurate radiotherapy more intuitively and truly.MethodsIn this study,a combined IC/IS applicator was designed by 3D printing technology,matched with the uterine cavity tube and implant needle to form an individualized applicator.The combined IC/IS applicator was applied into the pelvic phantom under the guidance of ultrasound and preoperative CT/MR registered image to realize multi-modal real-time image-guided precision brachytherapy for cervical cancer.Part1:A multi-modal real-time image guidance system was constructed,which mainly included: calibration and 3D reconstruction of ultrasonic probe using the prepared calibration template,the fast automatic registration algorithm of ultrasonic image and preoperative image,and a combined IC/IS applicator with a real-time spatial model.Marker experiments on the accuracy of real-time spatial model in CT images were performed using micro electromagnetic sensors.Part2:Pelvic phantom experiments were used to test the registration accuracy between US images and CT/MR images as well as the accuracy of the real-time position of the needle tip in the registered US images.Part3:A constructed animal pelvic model was used to simulate the real human abdominal tissue structure to verify the accuracy of guiding surgical needle placement in the case of US and preoperative CT/MR image registration.ResultsPart1 : In the marker experiments,the ultrasonic probe calibration error was0.272±0.081 mm.The ultrasonic probe calibration error in CT images was0.879±0.149 mm.Part2:In the pelvic phantom experiments,the difference of registration between US images and CT images was 0.935±0.166 mm in the axial plane and 0.916±0.143 mm in the sagittal plane.The difference of registration between needle trajectories and the needle’s real-time trajectories was 0.951±0.202 mm in registered US-CT images.The difference of registration between US images and MR images was1.01±0.223 mm in the axial plane and 1.04±0.207 mm in the sagittal plane.The difference of registration between needle trajectories and the needle’s real-time trajectories was 0.97±0.152 mm in registered US-MR images.No statistically significant differences were observed in the axial plane(p = 0.643),sagittal plane(p =0.072)and the needle’s real-time trajectories(p = 0.643)between the registered US-CT and US-MR images.Part3:In the animal pelvic model experiments,the average registration error of the real-time needle trajectory of the four implanted needles in the registered US-CT image was 1.009±0.012 mm with the average trajectory angle error of 1.91±0.61°.The average registration error in the registered US-MR image was 1.149±0.129 mm with the average trajectory angle error of 1.74 ± 0.57°.There was no significant difference between the registered US-CT images and US-MR images(p = 0.114).Conclusions1.2D ultrasound can complete rapid calibration and 3D reconstruction through the positioning device to realize the rapid registration between the real-time ultrasound images and the preoperative images.2.Under ideal conditions,high-precision image registration between real-time ultrasound-guided images and preoperative CT/MR images could be realized.At the same time,there was no significant difference in registration error between US-CT and US-MR registration images.3.In simulated human tissue,the registration between US images and CT/MR images still had high accuracy for real-time image guidance.During the same path implantation,there was no significant difference in the real-time trajectory of the needle between US-CT and US-MR registration images.