Zhouping Wei

Brachytherapy needle deflection evaluation and correction.

In prostate brachytherapy, an 18-gauge needle is used to implant radioactive seeds. This thin needle can be deflected from the preplanned trajectory in the prostate, potentially resulting in a suboptimum dose pattern and at times requiring repeated needle insertion to achieve optimal dosimetry. In this paper, we report on the evaluation of brachytherapy needle deflection and bending in test phantoms and two approaches to overcome the problem. First we tested the relationship between needle deflection and insertion depth as well as whether needle bending occurred. Targeting accuracy was tested by inserting a brachytherapy needle to target 16 points in chicken tissue phantoms. By implanting dummy seeds into chicken tissue phantoms under 3D ultrasound guidance, the overall accuracy of seed implantation was determined. We evaluated methods to overcome brachytherapy needle deflection with three different insertion methods: constant orientation, constant rotation, and orientation reversal at half of the insertion depth. Our results showed that needle deflection is linear with needle insertion depth, and that no noticeable bending occurs with needle insertion into the tissue and agar phantoms. A 3D principal component analysis was performed to obtain the population distribution of needle tip and seed position relative to the target positions. Our results showed that with the constant orientation insertion method, the mean needle targeting error was 2.8 mm and the mean seed implantation error was 2.9 mm. Using the constant rotation and orientation reversal at half insertion depth methods, the deflection error was reduced. The mean needle targeting errors were 0.8 and 1.2 mm for the constant rotation and orientation reversal methods, respectively, and the seed implantation errors were 0.9 and 1.5 mm for constant rotation insertion and orientation reversal methods, respectively.

3D TRUS guided robot assisted prostate brachytherapy

This paper describes a system for dynamic intraoperative prostate brachytherapy using 3D ultrasound guidance with robot assistance. The system consists of 3D transrectal ultrasound (TRUS) imaging, a robot and software for prostate segmentation, 3D dose planning, oblique needle segmentation and tracking, seed segmentation, and dynamic re-planning and verification. The needle targeting accuracy of the system was 0.79 mm +/- 0.32 mm in a phantom study.

Robotic-aided 3D TRUS guided intraoperative prostate brachytherapy

We have developed a robotic aided 3D transrectal ultrasound (TRUS) guided, intraoperative prostate brachytherapy. This system allows brachytherapy needles to be inserted into the prostate along various trajectories including oblique to avoid pubic arch interference. We unified the robotic coordinate system with the 3D TRUS image coordinate system. In addition, we also hdeveloped the method to automatically detect the needle in TRUS images for oblique insertion. We have evaluated our prototype system using prostate phantoms in terms of different needle insertion depths and the distances of the needle from the TRUS transducer. We have shown that our robotic aided 3D TRUS guided system was capable of placing the needle tip with approximately 0.74 mm ± 0.24 mm accuracy at a target identified in the 3D TRUS image. Brachytherapy accuracy was tested by dropping 0.8 mm beads into prostate phantoms via various angles up to ± 20°. Our results showed that the bead-dropping accuracy was 2.59 mm ± 0.76 mm with the error due to the needle deflection caused by the needles bevel.

Oblique needle segmentation for 3D TRUS-guided robot-aided transperineal prostate brachytherapy

3D TRUS-guided robot-aided prostate brachytherapy provides tools for dynamic re-optimization of a dose plan by freeing needle insertions from parallel trajectory constraints, i.e., needle trajectories can be positioned with considerable flexibility including oblique. However, oblique insertion results in the needle intersecting the 2D TRUS image and appearing as a dot, leading to blind guidance. Here, we propose a method for oblique needle segmentation and tracking to be used in a 3D TRUS guided and robot aided prostate brachytherapy system. This algorithm applies a grey-level change detection technique to find the location and orientation of needles from 3D images. Three 2D images containing the needle (oblique sagittal, coronal and transverse planes) are extracted and displayed in near real-time. Testing showed that our algorithm can find 3D needle orientation within 0.54/spl deg/ for a chicken tissue phantom, and 0.58/spl deg/ for agar phantoms, over a /spl plusmn/15/spl deg/ insertion orientation. The execution time averaged 0.13s on a 1.2 GHz computer.

Automated seed localization for intraoperative prostate brachytherapy based on 3D line segment patterns

Transrectal ultrasound (TRUS)-guided brachytherapy is a treatment option for localized prostate cancer, in which 125I or 103Pd radioactive seeds are implanted into the prostate. In this procedure, automated seed localization is important for intra-operative evaluation of dose delivery, which permits the identification of under-dosed regions and remedial seed placement, and ensures that the entire prostate receives the prescribed dose. In this paper, we describe the development of an automated seed segmentation method for use with 3D TRUS images. It is composed of five steps: 1) 3D needle segmentation; 2) volume cropping along the detected needle; 3) non-seed structure removal based on tri-bar model projection; 4) seed candidate recognition using 3D line segment detection; and 5) localization of seed positions. Experiments with the agar and chicken phantom images demonstrated that our method could segment 93% of the seeds in the 3D TRUS images with a mean distance error of 1.0 mm in an agar phantom and 1.7 mm in a chicken phantom, both with respect to manual segmented seed positions. The false positive rate was 7% while the segmentation time on a PC computer with dual AMD Athlon 1.8GHz processor was 280 seconds.

3D TRUS Image Segmentation in Prostate Brachytherapy

Brachytherapy is a minimally invasive interventional surgery used to treat prostate cancer. It is composed of three steps: dose pre-planning, implantation of radioactive seeds, and dose post-planning. In these procedures, it is crucial to determine the positions of needles and seeds, measure the volume of the prostate gland. Three-dimensional transrectal ultrasound (TRUS) imaging has been demonstrated to be a useful technique to perform such tasks. Compared to CT, MRI or X-ray imaging, US image suffers from low contrast, image speckle and shadows, making it challenging for segmentation of needles, the prostates and seeds in the 3D TRUS images. In this paper, we reviewed 3D TRUS image segmentation methods used in prostate brachytherapy including the segmentations of the needles, the prostate, as well as the seeds. Furthermore, some experimental results with agar phantom, turkey and chicken phantom, as well as the patient data are reported

Sci-Sat AM (2) Therapy-07: Feasibility of 3D ultrasound guided brachytherapy for lung cancer using a porcine lung tumour model

The standard treatment of localized early stage non‐small cell lungcancer is surgical resection. However, most patients are not candidates for surgery due to poor lung function and comorbidities. Minimally invasive interstitial brachytherapy may be an option for these patients. An in vivodosimetry test box was constructed to simulate the thoracic cavity and allow 3D ultrasound imaging of the brachytherapy needles. The box stabilizes the ultrasound probe and facilitates insertion of brachytherapy needles parallel to the probe axis. Seeds were implanted, targeted at the centre of a 1.5 cm agar sphere in 6% gelatin and then imaged using the 3D ultrasound and CT scans. The dosimetric impact of seed location was examined using Theraplan Plus. The DVH (dose volume histogram) was calculated assuming an I 125 seed activity that would cover the sphere with an arbitrary D90 of 25Gy if the seed was located at the centre of the sphere. DVH D90 values for the actual implanted seed positions will be presented comparing CT to ultrasound. This procedure was repeated in an ex vivolungtumourmodel consisting of agar spheres implanted into excised collapsed porcine lungs. Initial 3D ultrasound measurements were done with a probe designed for prostate brachytherapy. However, the measurements will be repeated with a smaller diameter thoracoscopic ultrasound probe that will be used clinically. This pilot work demonstrates the feasibility of using 3D ultrasound to target seed insertion and calculate dosimetry in a brachytherapylungtumourmodel.

MO‐E‐T‐618‐03: Dynamic Intraoperative Prostate Brachytherapy Using 3D TRUS Guidance with Robotic Assistance

Purpose: Develop a dynamic intraoperative prostate brachytherapy system, in which all phases of the procedure are performed in one session, including planning, monitoring of prostate changes, dynamic re-planning, optimal needle insertion including oblique trajectories and automatic seed localization in US images, to deal with variabilities in the current procedure. Method and Materials: The system consists of 3D TRUS imaging, a robot and software tools for prostate segmentation, intraoperative planning, oblique needle segmentation and tracking, seed segmentation, and 3D dose planning. The robot and 3D TRUS coordinate systems are unified with robot and image calibrations. In 3D TRUS images, the prostate is segmented using discrete dynamic contour method, and optimal implantation plan is performed by applying geometric optimization followed by simulated annealing. The robot can be controlled to guide the needle to target points in 3D TRUS images along oblique trajectories accurately and consistently. The inserted needles are segmented and tracked using grey-level change, and seed segmentation is performed using 3D line segment patterns. Results: Needle placement accuracy of the robot at “patient” skin was 0.15mm±0.06mm, and needle angulation error was 0.07°. Needle targeting accuracy was 0.79mm±0.32mm. The average difference between manual and the prostate segmentation algorithm of prostate boundaries was −0.20±0.28mm. In our needle tracking tests, errors in determining needle orientation were less than 2° in robot yaw and 0.7° in robot pitch orientations, for up to 20° needle insertion angles when the needle insertion distance was greater than 15mm. The true-positive rates for the seed segmentation algorithm in 3D TRUS images were 100% for agar and 93% for chicken phantoms. With optimal planning tools provided, 98% of prostate volume receives 80% of dose coverage. Conclusion: The result of this work provides a tool to achieve dynamic intraoperative prostate brachytherapy using 3D TRUS imaging and robotic assistance together with efficient segmentation software.

Segmentation of implanted radioactive seeds in 3D TRUS images for intraoperative prostate brachytherapy

Intraoperative prostate brachytherapy has potential to solve the problems in current brachytherapy, and verification of implanted seed locations in ultrasound (US) images is a necessary step in an intraoperative procedure. However, due to low quality of US images, and small size of radioactive seeds, it is difficult to achieve seed segmentation in US images. In this paper, we introduce an intraoperative seed segmentation algorithm in three-dimensional transrectal US images. A volumetric cone-beam flat-panel micro-CT scanner was used to evaluate the accuracy of the algorithm. We found that the rms error in determining seed locations using the algorithm was 0.98 mm in agar phantoms, and 1.02 mm in chicken phantoms

WE‐C‐330A‐05: Segmentation of Radioactive Seed in 3D Ultrasound Images for Intraoperative LDR Prostate Brachytherapy

Purpose: Develop and evaluate an algorithm to automatically localize implanted radioactive seeds in 3D ultrasoundimages for dynamic intraoperative low dose rate (LDR) brachytherapy procedures, in which all phases of the procedure are performed in one session to deal with variability in the current prostate brachytherapy.Method and Materials: Intraoperative seed segmentation in 3D TRUSimages is achieved by performing a subtraction of the image before the needle has been inserted, and the image after the seeds have been implanted. The seeds are searched through a thresholding operation in a “local” space determined by the needle position and orientation information, which are obtained from a needle segmentation algorithm. To test this approach, 3D TRUSimages of the agar and chicken tissue phantoms were obtained. Within these phantoms, dummy seeds were implanted. The seed locations determined by the seed segmentation algorithm were compared with those obtained from a volumetric cone‐beam flat‐panel micro‐CT scanner and human observers. Results: Evaluation of the algorithm showed that, the rms error in determining the seed locations using the seed segmentation algorithm was 0.98mm in agar phantoms, and 1.02mm in chicken phantoms. In both agar and chicken phantoms, 100% of the implanted seeds were correctly identified using the seed segmentation algorithm. Conclusions: The seed segmentation algorithm is insensitive to different materials, as the errors of the algorithm are almost the same in agar and chicken phantoms. This work indicates the potential to achieve an intraoperative post‐implant dosimetry. Integration of this algorithm into a clinical brachytherapy system is now ongoing and clinical testing with patients will take place in the near future.