Brachytherapy Needle Research Articles

Fiber Bragg gratings-based sensing for real-time needle tracking during MR-guided brachytherapy.

The development of MR-guided high dose rate (HDR) brachytherapy is under investigation due to the excellent tumor and organs at risk visualization of MRI. However, MR-based localization of needles (including catheters or tubes) has inherently a low update rate and the required image interpretation can be hampered by signal voids arising from blood vessels or calcifications limiting the precision of the needle guidance and reconstruction. In this paper, a new needle tracking prototype is investigated using fiber Bragg gratings (FBG)-based sensing: this prototype involves a MR-compatible stylet composed of three optic fibers with nine sets of embedded FBG sensors each. This stylet can be inserted into brachytherapy needles and allows a fast measurement of the needle deflection. This study aims to assess the potential of FBG-based sensing for real-time needle (including catheter or tube) tracking during MR-guided intervention. First, the MR compatibility of FBG-based sensing and its accuracy was evaluated. Different known needle deflections were measured using FBG-based sensing during simultaneous MR-imaging. Then, a needle tracking procedure using FBG-based sensing was proposed. This procedure involved a MR-based calibration of the FBG-based system performed prior to the interventional procedure. The needle tracking system was assessed in an experiment with a moving phantom during MR imaging. The FBG-based system was quantified by comparing the gold-standard shapes, the shape manually segmented on MRI and the FBG-based measurements. The evaluation of the MR compatibility of FBG-based sensing and its accuracy shows that the needle deflection could be measured with an accuracy of 0.27 mm on average. Besides, the FBG-based measurements were comparable to the uncertainty of MR-based measurements estimated at half the voxel size in the MR image. Finally, the mean(standard deviation) Euclidean distance between MR- and FBG-based needle position measurements was equal to 0.79 mm(0.37 mm). The update rate and latency of the FBG-based needle position measurement were 100 and 300 ms, respectively. The FBG-based needle tracking procedure proposed in this paper is able to determine the position of the complete needle, under MR-imaging, with better accuracy and precision, higher update rate, and lower latency compared to current MR-based needle localization methods. This system would be eligible for MR-guided brachytherapy, in particular, for an improved needle guidance and reconstruction.

Sci‐Thur AM: YIS – 03: Combining sagittally‐reconstructed 3D and live‐2D ultrasound for high‐dose‐rate prostate brachytherapy needle segmentation

Ultrasound‐guided high‐dose‐rate prostate brachytherapy (HDR‐BT) needle segmentation is performed clinically using live‐2D sagittal images. Organ segmentation is then performed using axial images, introducing a source of geometric uncertainty. Sagittally‐reconstructed 3D (SR3D) ultrasound enables both needle and organ segmentation, but suffers from shadow artifacts. We present a needle segmentation technique augmenting SR3D with live‐2D sagittal images using mechanical probe tracking to mitigate image artifacts and compare it to the clinical standard.Seven prostate cancer patients underwent TRUS‐guided HDR‐BT during which the clinical and proposed segmentation techniques were completed in parallel using dual ultrasound video outputs. Calibrated needle end‐length measurements were used to calculate insertion depth errors (IDEs), and the dosimetric impact of IDEs was evaluated by perturbing clinical treatment plan source positions.The proposed technique provided smaller IDEs than the clinical approach, with mean±SD of −0.3±2.2 mm and −0.5±3.7mm respectively. The proposed and clinical techniques resulted in 84% and 43% of needles with IDEs within ±3mm, and IDE ranges across all needles of [−7.7mm, 5.9mm] and [−9.3mm, 7.7mm] respectively. The proposed and clinical IDEs lead to mean±SD changes in the volume of the prostate receiving the prescription dose of −0.6±0.9% and −2.0±5.3% respectively.The proposed technique provides improved HDR‐BT needle segmentation accuracy over the clinical technique leading to decreased dosimetric uncertainty by eliminating the axial‐to‐sagittal registration, and mitigates the effect of shadow artifacts by incorporating mechanically registered live‐2D sagittal images.

Abstract 3900: Sustained release of PARP inhibitor Talazoparib and chemotherapeutics from biodegradable implants for treatment of breast and prostate cancer

Abstract Sustained localized delivery of cancer therapeutics is a safe and effective unique option for non-metastatic cancers. Here we report a novel biodegradable implant with the capability to encapsulate therapeutics, molecular agents, or nanoparticles for local intratumoral delivery. We have successfully demonstrated in vivo the delivery of PARP inhibitor Talazoparib to treat Brca1-mutated cancers and Docetaxel to treat localized or recurring prostate cancers. This one-time intratumoral injection provides a safe vehicle for the sustained release of PARP inhibitor Talazoparib and chemotherapeutic Docetaxel in contrast to low bioavailability and toxicity associated with oral or systemic delivery. Methods: Biodegradable implants of 1-2mm length and 0.8mm diameter were loaded with ∼50μg Talazoparib (BMN) for BRCA1-mutated breast cancer (BCa) studies and ∼500μg Docetaxel (DTX) for prostate cancer (PCa) studies. Implants were characterized using SEM and HPLC, and release studies were carried out in pH 6.0 PBS buffer at 37°C. The IC50's were determined using an MTS assay in cell lines W0069 and W780 (BCa) and PC3 (PCa). In vivo studies were carried out in Brca1 Co/Co;MMTV-Cre; p53+/− spontaneous tumored mice for BCa studies. Subcutaneous PC3 tumors were xenografted in nude mice. PCa studies were done with and without radiation. Implants were injected once intratumorally using an 18G brachytherapy needle. Results: The release profile of the drug from the implant in buffer showed a highly sustained release for multiple weeks at therapeutically relevant doses for both DTX and BMN loaded implants. BCa cell lines W0069 and W780 were highly sensitive to BMN, most likely due to Brca1 mutation. Following a one-time intratumoral implantation of BMN, tumors reduced in size by an average of 50%, while untreated tumors increased ∼5X in size. BMN dosing appeared to be well tolerated by the mice. DTX implants proved to be an effective method for PCa treatment in vivo with no weight loss observed. The local DTX group showed sustained tumor inhibition compared to empty implants and an equivalent DTX dose given systemically. At 40 days 89% survival was observed for mice treated with localized DTX implants compared with 0% in all other treatment groups. Histology samples were taken from sacrificed mice and immunohistochemistry is currently underway. Conclusions: Sustained local release of therapeutically relevant doses of BMN and DTX were observed in vitro and in vivo. Therapeutics loaded in implants represent a novel delivery modality that is well-tolerated. Sustained release of BMN appears to amplify the therapeutic efficacy of PARP inhibition in BRCA1 mutated breast cancers and sustained release of DTX is an effective chemotherapy option alone or in combination with radiation therapy. These results lay a strong foundation for the use of localized biodegradable implants for the treatment of breast and prostate cancer. Citation Format: Jodi Belz, Noelle Castilla Ojo, Paige Baldwin, Rajiv Kumar, Anne van de Ven, Karen Liby, Robert Cormack, Mike Makrigiorgos, Srinivas Sridhar. Sustained release of PARP inhibitor Talazoparib and chemotherapeutics from biodegradable implants for treatment of breast and prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3900.

WE-FG-BRA-02: Docetaxel Eluting Brachytherapy Spacers for Local Chemo-Radiation Therapy in Prostate Cancer

Purpose: We propose an innovative combinatorial treatment strategy of Local ChemoRadiation Therapy (LCRT) using a sustained drug delivery platform in the form of a spacer to locally radio-sensitize the prostate with Docetaxel (DTX) enabling a synergistic cure with the use of lower radiation doses. These biodegradable spacers are physically similar to the inert spacers routinely used in prostate brachytherapy but are now loaded with formulations of DTX. Methods: Spacers were loaded with ∼500µg Docetaxel (DTX) for prostate cancer studies. The implants were characterized in vitro using SEM and HPLC. The release kinetic studies were carried out in buffer (pH 6.0) at 37°C. Subcutaneous PC3 tumors were xenografted in nude mice. Prostate cancer studies were done with and without radiation using SARRP at 5Gy, 10Gy, and 15Gy. Drug-loaded implants were injected once intratumorally using an 18G brachytherapy needle. Results: The release study in vitro showed a highly sustained release for multiple weeks at therapeutically relevant doses. The monotherapy with local DTX spacer showed sustained tumor inhibition compared to empty implants and an equivalent DTX dose given systemically. At 40 days, 89% survival was observed for mice treated with DTX implants compared with 0% in all other treatment groups. The combined treatment with local DTX spacer and radiation (10Gy) showed the highest degree of tumor suppression (significant tumor growth inhibition by day 90). The control mice showed continuous tumor growth and were scarified by day 56. Groups of mice treated with DTX-spacer or radiation alone showed initial tumor suppression but growth continued after day 60. A larger experiment is ongoing. Conclusion: This approach provides localized delivery of the chemotherapeutic sensitizer directly to the tumor and avoids the toxicities associated with both brachytherapy and current systemic delivery of docetaxel. Sustained release of DTX is an effective chemotherapy option alone or in combination with radiation therapy.

Source strength verification and quality assurance of preloaded brachytherapy needles using a CMOS flat panel detector.

Current methods of low dose rate brachytherapy source strength verification for sources preloaded into needles consist of either assaying a small number of seeds from a separate sample belonging to the same lot used to load the needles or performing batch assays of a subset of the preloaded seed trains. Both of these methods are cumbersome and have the limitations inherent to sampling. The purpose of this work was to investigate an alternative approach that uses an image-based, autoradiographic system capable of the rapid and complete assay of all sources without compromising sterility. The system consists of a flat panel image detector, an autoclavable needle holder, and software to analyze the detected signals. The needle holder was designed to maintain a fixed vertical spacing between the needles and the image detector, and to collimate the emissions from each seed. It also provides a sterile barrier between the needles and the imager. The image detector has a sufficiently large image capture area to allow several needles to be analyzed simultaneously.Several tests were performed to assess the accuracy and reproducibility of source strengths obtained using this system. Three different seed models (Oncura 6711 and 9011 (125)I seeds, and IsoAid Advantage (103)Pd seeds) were used in the evaluations. Seeds were loaded into trains with at least 1 cm spacing. Using our system, it was possible to obtain linear calibration curves with coverage factor k = 1 prediction intervals of less than ±2% near the centre of their range for the three source models. The uncertainty budget calculated from a combination of type A and type B estimates of potential sources of error was somewhat larger, yielding (k = 1) combined uncertainties for individual seed readings of 6.2% for (125)I 6711 seeds, 4.7% for (125)I 9011 seeds, and 11.0% for Advantage (103)Pd seeds. This study showed that a flat panel detector dosimetry system is a viable option for source strength verification in preloaded needles, as it is capable of measuring all of the sources intended for implantation. Such a system has the potential to directly and efficiently estimate individual source strengths, the overall mean source strength, and the positions within the seed-spacer train.

A Hand-Held Assistant for Semiautomated Percutaneous Needle Steering.

Permanent prostate brachytherapy is an effective and popular treatment modality for prostate cancer in which long needles are inserted into the prostate. Challenges associated with manual needle insertion such as needle deflection limit this procedure to primarily treat the entire prostate gland even for patients with localized cancer. In this paper, we present a new semiautomated hand-held needle steering assistant designed to help surgeons improve needle placement accuracy. Regular clinical brachytherapy needles are connected to a compact device that the surgeon holds. As the surgeon inserts the needle, the device rotates the needle base on a measured and calculated basis in order to produce a desired trajectory of the needle tip. A novel needle-tissue interaction model and a steering algorithm calculate such control actions based on ultrasound images of the needle in tissue. The assistant can also apply controlled longitudinal microvibrations to the needle that reduce needle-tissue friction. Experimental validation of the proposed system in phantom and ex-vivo biological tissue report an average needle targeting accuracy of 0.33 mm over 72 needle insertions in 12 different experimental scenarios. We introduce a new framework for needle steering in prostate brachytherapy in which the surgeon remains in charge of the needle insertion. The device weighs 160 g, making it easy to incorporate with current insertion techniques. Expected benefits of the proposed system include more precise needle targeting accuracy, which can result in improved focal treatment of prostate cancer.

Abstract B42: Sustained release of PARP inhibitor Talazoparib from bioedgradable implant for treatment of BRCA1-mutated breast cancer

Abstract The breast cancer-associated gene 1 (Brca1) is the most frequently mutated tumor suppressor gene found in familial breast cancers. Mutations of the gene modulate many cellular functions including DNA damage and repair, homologous recombination, cell-cycle regulation, and apoptosis. Poly-ADP-Ribose Polymerase (PARP) inhibitor therapy can produce cell death in cancers with genetic predispositions for impaired DNA repair or transcription pathways such as Brca1 mutants. Here we report a novel biodegradable implant for the local delivery of PARP inhibitor Talazoparib to treat Brca1-mutated cancers. This one-time intratumoral injection provides a safe vehicle for the sustained release of PARP inhibitor Talazoparib in contrast to low bioavailability and toxicity associated with oral delivery. Methods: Biodegradable implants of 1-2mm length and 0.8mm diameter were loaded with ∼50μg Talazoparib. The implants were characterized in vitro using SEM and HPLC, and the release kinetic studies were carried out in PBS buffer (pH 6.0) at 37°C. The IC50 was determined using an MTS assay in breast cancer cell lines derived from Brca1 Co/Co; MMTV-Cre; p53+/−mice. In vivo studies were carried out in Brca1 Co/Co; MMTV-Cre; p53+/− mice. Drug-loaded implants were injected once intratumorally using an 18G brachytherapy needle. Results: In vitro studies The release profile of the drug from the implant in buffer showed a highly sustained release for multiple weeks at therapeutically relevant doses. Breast cancer cell lines W0069 and W780, derived from Brca1 Co/Co; MMTV-Cre; p53+/− mice were highly sensitive to Talazoparib, most likely due to Brca1 mutation. PARP expression was examined via western blot analysis. In vivo studies In vivo studies using sustained drug release implants loaded with Talazoparib were also carried out in Brca1Co/Co;MMTV-Cre;p53+/- genetically engineered mice with 1 or more spontaneous breast tumors. Following a one-time implantation, tumors reduced in size by an average of 50%, while untreated tumors increased ∼5X in size. Talazoparib dosing appeared to be well tolerated by the mice. Histology samples were taken from sacrificed mice and immunohistochemistry are currently underway. Conclusions: Sustained local release of therapeutically relevant doses of Talazoparib was observed in vitro and in vivo. The Talazoparib-loaded implants represent a novel delivery route that was well-tolerated. Sustained release of Talazoparib appears to amplify the therapeutic efficacy of PARP inhibition and is a promising new route for the treatment of highly aggressive breast cancer models. We would like to acknowledge the Breast Cancer Research Foundation. This work was supported by the Army- W81XWH-14-1-0092 and Northeastern University – Dana Farber Cancer Institute collaborative grant. Citation Format: Jodi Belz, Karen Liby, Paige Baldwin, Rajiv Kumar, Anne L. van de Ven, Robert Cormack, Mike Makrigiorgos, Srinivas Sridhar. Sustained release of PARP inhibitor Talazoparib from bioedgradable implant for treatment of BRCA1-mutated breast cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B42.

Development of an MRI-Compatible Needle Driver for In-Bore Prostate Biopsy.

Minimally invasive percutaneous approaches routinely employ insertion of needles into soft tissue for diagnostic or therapeutic purposes. Lack of targeting accuracy while inserting needles can significantly mitigate the effectiveness of these methods. Robot-assisted needle steering under magnetic resonance imaging (MRI) guidance is a viable option for reaching the target accurately. In this paper, we report the development of an MRI-compatible needle driver for in-bore prostate biopsy. The device easily mounts onto and works together with our previously developed MRI-compatible prostate interventional robot. It is the first robotic device using a standard biopsy gun, which is easily replaceable/detachable in case of multi-sampling biopsy applications. The mechanism enables rotation, translation, and triggering of the biopsy gun to steer the bevel needle through the tissue and to take samples accurately from the target loci. Using the rotational and translational capabilities, the same system can also assist brachytherapy needle placement. Preliminary experiments have shown that the design meets the requirements set by the clinical workflow. System feasibility was verified by multiple users inserting 2 different types of needles under visual feedback into a phantom made of soft plastic. The average targeting errors were 0.92 mm for 18 gauge biopsy and 1.65 mm for 20 gauge brachytherapy needle.

SU-F-BRA-04: Prostate HDR Brachytherapy with Multichannel Robotic System

Purpose: High-dose-rate (HDR) brachytherapy is gradually becoming popular in treating patients with prostate cancers. However, placement of the HDR needles at desired locations into the patient is challenging. Application of robotic system may improve the accuracy of the clinical procedure. This experimental study is to evaluate the feasibility of using a multichannel robotic system for prostate HDR brachytherapy. Methods: In this experimental study, the robotic system employed was a 6-DOF Multichannel Image-guided Robotic Assistant for Brachytherapy (MIRAB), which was designed and fabricated for prostate seed implantation. The MIRAB has the provision of rotating 16 needles while inserting them. Ten prostate HDR brachytherapy needles were simultaneously inserted using MIRAB into a commercially available prostate phantom. After inserting the needles into the prostate phantom at desired locations, 2mm thick CT slices were obtained for dosimetric planning. HDR plan was generated using Oncetra planning system with a total prescription dose of 34Gy in 4 fractions. Plan quality was evaluated considering dose coverage to prostate and planning target volume (PTV), with 3mm margin around prostate, as well as the dose limit to the organs at risk (OARs) following the American Brachytherapy Society (ABS) guidelines. Results: From the CT scan, it is observed that the needles were inserted straight into the desired locations and they were adequately spaced and distributed for a clinically acceptable HDR plan. Coverage to PTV and prostate were about 91% (V100= 91%) and 96% (V100=96%), respectively. Dose to 1cc of urethra, rectum, and bladder were within the ABS specified limits. Conclusion: The MIRAB was able to insert multiple needles simultaneously into the prostate precisely. By controlling the MIRAB to insert all the ten utilized needles into the prostate phantom, we could achieve the robotic HDR brachytherapy successfully. Further study for assessing the system's performance and reliability is in progress.

CT-Guided Radioactive Seed Implantation as a Salvage Modality for Locally Recurrent Rectal Cancer

well meet the treatment requirement. The mean entrance point positioning deviation was 0.883 mm (range 0.002 to 2.943 mm) in different sites. The mean orientation deviation were 1.977 (range 0.536 to 4.566 ). All needles arrived the preplanned position in 1 attempt manually. The mean time to insert one needle is 7.5 seconds. Conclusions: This study demonstrates that 3D printing individual templates can acurately confirm the position and direction of needles in brachytherapy, and achieve effectively transfer from preplan to clinical operations. 3D printing individual template can enhance implantation accuracy, as well as simplifying the procedure. It is a simple and effective way to guide needle insertion in head and neck, because of the complex structures and existence of many organs at risk.

Virtual Planning of Needle Trajectories Using a Haptic Interface for a Brachytherapy Parallel Robot: An Evaluation Study

Brachytherapy (BT) is a modality to treat cancer by inserting needles into a patient to deliver radioactive sources direct to the diseased tissue. The efficiency of the treatment is determined by the positions of the needles. A robot can be used in order to increase the precision of the needles locations. This paper presents an approach for needle trajectory planning based on isomorphic mapping from a haptic device. A virtual reality environment has been modelled containing a 3D reconstructed abdominal model of the patient. Needle insertion using the BT robot is controlled using a Force Dimension Omega haptic device. The developed software application allows the users to practice robotic needle insertion and to determine the most appropriate locations for the BT needles.

Kinematic Modelling of a New 5-DOF (Axis) Parallel Robot Used in Brachytherapy

The paper presents a new medical parallel robot for brachytherapy. Brachytherapy (BT) is a relatively new and efficient medical technique for cancer treatment that enables to deliver higher doses of radiation to more-specific areas of the body, compared to the conventional form of radiation therapy that projects radiation from a machine outside the body. BT implies the implant of radioactive seeds inside the tumor, through specific needles, thus affecting only the tumor while avoiding unnecessary irradiation of the healthy tissue. Compared to the most of the brachytherapy designed only for treating the prostate, the medical robot presented in the paper is designed for hard-to-reach areas (such as the retroperitoneal area or the mediastinum). An approach regarding the robot structural synthesis, kinematics is presented followed by some simulation results obtained for a specific BT needle trajectory.

Segmentation, Separation and Pose Estimation of Prostate Brachytherapy Seeds in CT Images.

In this paper, we address the development of an automatic approach for the computation of pose information (position + orientation) of prostate brachytherapy loose seeds from 3-D CT images. From an initial detection of a set of seed candidates in CT images using a threshold and connected component method, the orientation of each individual seed is estimated by using the principal components analysis method. The main originality of this approach is the ability to classify the detected objects based on a priori intensity and volume information and to separate groups of closely spaced seeds using three competing clustering methods: the standard and a modified k-means method and a Gaussian mixture model with an expectation-maximization algorithm. Experiments were carried out on a series of CT images of two phantoms and patients. The fourteen patients correspond to a total of 1063 implanted seeds. Detections are compared to manual segmentation and to related work in terms of detection performance and calculation time. This automatic method has proved to be accurate and fast including the ability to separate groups of seeds in a reliable way and to determine the orientation of each seed. Such a method is mandatory to be able to compute precisely the real dose delivered to the patient postoperatively instead of assuming the alignment of seeds along the theoretical insertion direction of the brachytherapy needles.

In vivovisualization of prostate brachytherapy seeds with photoacoustic imaging

We conducted a canine study to investigate the in vivo feasibility of photoacoustic imaging for intraoperative updates to brachytherapy treatment plans. A fiber coupled to a 1064-nm Nd:YAG laser was inserted into high-dose-rate brachytherapy needles, which diffused light spherically. These needles were inserted through the perineum into the prostate for interstitial light delivery and the resulting acoustic waves were detected with a transrectal ultrasound probe. Postoperative computed tomography images and ex vivo photoacoustic images confirmed seed locations. Limitations with insufficient light delivery were mitigated with short-lag spatial coherence (SLSC) beamforming, providing a 10-20 dB contrast improvement over delay-and-sum (DAS) beamforming for pulse energies ranging from 6.8 to 10.5 mJ with a fiber-seed distance as large as 9.5 mm. For the same distance and the same range of energy densities, signal-to-noise ratios (SNRs) were similar while the contrast-to-noise ratio (CNR) was higher in SLSC compared to DAS images. Challenges included visualization of signals associated with the interstitial fiber tip and acoustic reverberations between seeds separated by ≤ 2 mm. Results provide insights into the potential for clinical translation to humans.

Kinematic analysis of a new 5-DOF modular parallel robot for brachytherapy

Abstract Cancer represents one of the main causes of the death. Huge efforts have been made by the scientific community to provide better cancer treatment solutions. An innovative option is the brachytherapy (BT), a local radiation technique for cancer treatment, which enables the delivery of high doses of radiation inside the tumors. BT usage is limited by the insufficient accuracy of the radioactive seeds placement. In order to eliminate these limitations, the authors propose an innovative modular structure which would enable the precise positioning of the BT needles in any part of the patient body. The paper presents the kinematic modeling of the new 5-DOF robotic structure. The workspace analysis and the singularities are studied and the dexterous workspace for a given insertion point inside the patient is also shown. Finally, some numerical simulations of different BT needle trajectories are included.

WE-A-17A-09: Exploiting Electromagnetic Technologies for Real-Time Seed Drop Position Validation in Permanent Implant Brachytherapy

Purpose: To report on preliminary results validating the performance of a specially designed LDR brachytherapy needle prototype possessing both electromagnetic (EM) tracking and seed drop detection abilities. Methods: An EM hollow needle prototype has been designed and constructed in collaboration with research partner Philips Healthcare. The needle possesses conventional 3D tracking capabilities, along with a novel seed drop detection mechanism exploiting local changes of electromagnetic properties generated by the passage of seeds in the needle's embedded sensor coils. These two capabilities are exploited by proprietary engineering and signal processing techniques to generate seed drop position estimates in real-time treatment delivery. The electromagnetic tracking system (EMTS) used for the experiment is the NDI Aurora Planar Field Generator. The experiment consisted of dropping a total of 35 seeds in a prismatic agarose phantom, and comparing the 3D seed drop positions of the EMTS to those obtained by an image analysis of subsequent micro-CT scans. Drop position error computations and statistical analysis were performed after a 3D registration of the two seed distributions. Results: Of the 35 seeds dropped in the phantom, 32 were properly detected by the needle prototype. Absolute drop position errors among the detected seeds ranged from 0.5 to 4.8 mm with mean and standard deviation values of 1.6 and 0.9 mm, respectively. Error measurements also include undesirable and uncontrollable effects such as seed motion upon deposition. The true accuracy performance of the needle prototype is therefore underestimated. Conclusion: This preliminary study demonstrates the potential benefits of EM technologies in detecting the passage of seeds in a hollow needle as a means of generating drop position estimates in real-time treatment delivery. Such tools could therefore represent a potentially interesting addition to existing brachytherapy protocols for rapid dosimetry validation. Equipments and fundings for this project were provided by Philips Medical.

SU-D-BRF-06: A Brachytherapy Simulator with Realistic Haptic Force Feedback and Real-Time Ultrasounds Image Simulation for Training and Teaching

Purpose: Surgical procedures require dexterity, expertise and repetition to reach optimal patient outcomes. However, efficient training opportunities are usually limited. This work presents a simulator system with realistic haptic force-feedback and full, real-time ultrasounds image simulation. Methods: The simulator is composed of a custom-made Linear-DELTA force-feedback robotic platform. The needle tip is mounted on a force gauge at the end effector of the robot, which responds to needle insertion by providing reaction forces. 3D geometry of the tissue is using a tetrahedral finite element mesh (FEM) mimicking tissue properties. As the needle is inserted/retracted, tissue deformation is computed using a mass-tensor nonlinear visco-elastic FEM. The real-time deformation is fed to the L-DELTA to take into account the force imparted to the needle, providing feedback to the end-user when crossing tissue boundaries or needle bending. Real-time 2D US image is also generated synchronously showing anatomy, needle insertion and tissue deformation. The simulator is running on an Intel I7 6- core CPU at 3.26 MHz. 3D tissue rendering and ultrasound display are performed on a Windows 7 computer; the FEM computation and L-DELTA control are executed on a similar PC using the Neutrino real-time OS. Both machines communicate through an Ethernet link.more » Results: The system runs at 500 Hz for a 8333-tetrahedron tissue mesh and a 100-node angular spring needle model. This frame rate ensures a relatively smooth displacement of the needle when pushed or retracted (±20 N in all directions at speeds of up to 2 m/s). Unlike commercially-available haptic platforms, the oblong workspace of the L-DELTA robot complies with that required for brachytherapy needle displacements of 0.1m by 0.1m by 0.25m. Conclusion: We have demonstrated a real-life, realistic brachytherapy simulator developed for prostate implants (LDR/HDR). The platform could be adapted to other sites or training for other types of needle-based procedures.« less

Customized Needle Guides for Inserting Non-Parallel Needle Arrangements in Prostate HDR Brachytherapy: A Phantom Study

Purpose: To evaluate the use of customized guides for inserting optimized, non-parallel arrangements of high-dose-rate (HDR) brachytherapy needles into prostate gelatin phantoms. Materials and Methods: Four prostate gelatin phantoms were constructed with prostate, urethra, bladder, rectum, penile bulb, and pubic arch anatomical structures. The target volume was the prostate, and the other structures were organs at risk (OAR). The anatomical structures were digitized, and a non-parallel needle arrangement was optimized for each phantom using Needle Planning by Integer Program (NPIP). The optimized needle arrangements contained 13-15 needles, which is less than the standard number currently used in our clinic. None of the optimized needles punctured any non-prostate structures. Inverse Planning by Integer Program (IPIP) was used to compute a dose plan for each optimized needle arrangement that conformed to the guidelines set in the Radiation Therapy Oncology Group (RTOG) 0321 dosimetric protocol. Customized needle guides were digitally created for each phantom to implant the corresponding optimized needle arrangement. The needle guides were 3D-printed in ABS plastic using a uPrint Plus 3D printer (StrataSys). The needle guides were mechanically registered to the phantoms. The needles were inserted into each phantom by a researcher without any clinical brachytherapy experience and without the assistance of trans-rectal ultrasound (TRUS) guidance. The phantoms and implanted needle arrangements were digitized, and another dose plan was computed for each implant. Compliance with the RTOG 0321 protocol, puncturing of OAR, and placement error were evaluated. Results: Three of the needle arrangements were implanted without puncturing any OAR. Due to placement error, one implanted needle arrangement punctured the penile bulb and urethra. We considered this case a failure, and we did not post-process it further. The successfully implanted needle arrangements met all the dose requirements in the RTOG 0321 protocol. The RMS placement error between the dwell positions in the planned and implanted needle arrangements was 3.6 mm, 4.5 mm, and 2.3 mm for the three cases. The majority of the error was along the needle insertion direction (i.e. the z-direction), which is most likely because templates do not restrict motion along this direction, and therefore is where error is the most user-dependent, or because the anatomy was digitized from 3 mm thick CT slices taken in the zdirection, and therefore registration in this direction is the most uncertain. Conclusions: Customized needle guides are a promising method for inserting optimized, non-parallel, brachytherapy needle arrangements. Although NPIP, IPIP, and 3D printers were used to construct the guides in this study, other planning and construction methods could be used without changing our fundamental workflow structure. However, the templatepatient registration and needle insertion workflow must still be improved to reduce placement error. This includes incorporating real-time TRUS guidance to monitor progress and avoid puncturing OAR, which we propose as future work.

Needle deflection estimation: prostate brachytherapy phantom experiments

The performance of a fusion-based needle deflection estimation method was experimentally evaluated using prostate brachytherapy phantoms. The accuracy of the needle deflection estimation was determined. The robustness of the approach with variations in needle insertion speed and soft tissue biomechanical properties was investigated. A needle deflection estimation method was developed to determine the amount of needle bending during insertion into deformable tissue by combining a kinematic deflection model with measurements taken from two electromagnetic trackers placed at the tip and the base of the needle. Experimental verification of this method for use in prostate brachytherapy needle insertion procedures was performed. A total of 21 beveled tip, 18 ga, 200 mm needles were manually inserted at various speeds through a template and toward different targets distributed within 3 soft tissue mimicking polyvinyl chloride prostate phantoms of varying stiffness. The tracked positions of both the needle tip and base were recorded, and Kalman filters were applied to fuse the sensory information. The estimation results were validated using ground truth obtained from fluoroscopy images. The manual insertion speed ranged from 8 to 34 mm/s, needle deflection ranged from 5 to 8 mm at an insertion depth of 76 mm, and the elastic modulus of the soft tissue ranged from 50 to 150 kPa. The accuracy and robustness of the estimation method were verified within these ranges. When compared to purely model-based estimation, we observed a reduction in needle tip position estimation error by [Formula: see text] % (mean [Formula: see text] SD) and the cumulative deflection error by [Formula: see text] %. Fusion of electromagnetic sensors demonstrated significant improvement in estimating needle deflection compared to model-based methods. The method has potential clinical applicability in the guidance of needle placement medical interventions, particularly prostate brachytherapy.

A training phantom for ultrasound-guided needle insertion and suturing

During gynecologic brachytherapy (BT), suturing and image-guided needle insertions are highly skill-dependent tasks. Medical residents often have to practice these techniques in the operating room; this is sub-optimal for many reasons. We present a fast and low-cost method of building realistic and disposable gynecologic phantoms, which can be used to train physicians new to gynecologic BT. Phantoms comprised a rectal cavity large enough to accommodate a standard transrectal ultrasound (US) probe, a vaginal cavity, a uterus, a uterine canal, and a cervix, all embedded in a gelatin matrix. The uterus was made of gelatin and coated with rubber to mimic the texture of soft tissue and for computed tomography (CT) and US image contrast. The phantom's durability, longevity, construction times, materials costs, CT, and US image quality were recorded. The speed of sound in the gelatin was measured using pulse echo measurements. Anatomic structures were distinguishable using CT and US. For the first phantom, material costs were under $200, curing time was approximately 48 hours, and active participation time was 3 hours. Reusable parts allowed for reduction in time and cost for subsequent phantoms: under $20, 24 hours curing time, and 1 hour active participation time. The speed of sound in the gelatin ranged from 1495 to 1506m/s. A method for constructing gelatin gynecologic phantoms was developed. It can be used for training in image-guided BT needle insertion, placing a suture on the vaginal wall, and suturing the cervical lip.