Closed loop control of a robot assisted smart flexible needle for percutaneous intervention.

This paper presents the experimental evaluation of a coordinated control system for a robot and robot-driven shape memory alloy (SMA) actuated smart flexible needle capable of following a curved path for percutaneous intervention. The robot driving the needle is considered the outer loop and the non-linear SMA actuated flexible needle system comprises the inner loop. The two feedback control loops are coordinated in such a way that the robot drives the needle while monitoring the needle's actual deflection against a preplanned ideal trajectory, so that the needle tip reaches the target location within an acceptable accuracy. In air and in water experimental results are presented to validate the ability of the proposed coordinated controller to track the overall desired trajectory which includes the combined trajectory of the robot driver and the needle.

Implementation and experimental results of 4D tumor tracking using robotic couch.

PURPOSE: This study presents the implementation and experimental results of a novel technique for 4D tumor tracking using a commercially available and commonly used treatment couch and evaluates the tumor tracking accuracy in clinical settings. METHODS: Commercially available couch is capable of positioning the patient accurately; however, currently there is no provision for compensating physiological movement using the treatment couch in real-time. In this paper, a real-time couch tracking control technique is presented together with experimental results in tumor motion compensation in four dimensions (superior-inferior, lateral, anterior-posterior, and time). To implement real-time couch motion for tracking, a novel control system for the treatment couch was developed. The primary functional requirements for this novel technique were: (a) the treatment couch should maintain all previous∕normal features for patient setup and positioning, (b) the new control system should be used as a parallel system when tumor tracking would be deployed, and (c) tracking could be performed in a single direction and∕or concurrently in all three directions of the couch motion (longitudinal, lateral, and vertical). To the authors' best knowledge, the implementation of such technique to a regular treatment couch for tumor tracking has not been reported so far. To evaluate the performance of the tracking couch, we investigated the mechanical characteristics of the system such as system positioning resolution, repeatability, accuracy, and tracking performance. Performance of the tracking system was evaluated using dosimetric test as an endpoint. To investigate the accuracy of real-time tracking in the clinical setting, the existing clinical treatment couch was replaced with our experimental couch and the linear accelerator was used to deliver 3D conformal radiation therapy (3D-CRT) and intensity modulated radiation therapy (IMRT) treatment plans with and without tracking. The results of radiation dose distribution from these two sets of experiments were compared and presented here. RESULTS: The mechanical accuracies were 0.12, 0.14, and 0.18 mm in X, Y, and Z directions. The repeatability of the desired motion was within ±0.2 mm. The differences of central axis dose between the 3D-CRT stationary plan and two tracking plans with different motion trajectories were 0.21% and 1.19%. The absolute dose differences of both 3D tracking plans comparing to the stationary plan were 1.09% and 1.20%. Comparing the stationary IMRT plan with the tracking IMRT plan, it was observed that the central axis dose difference was -0.87% and the absolute difference of both IMRT plans was 0.55%. CONCLUSIONS: The experimental results revealed that the treatment couch could be successfully used for real-time tumor tracking with a high level of accuracy. It was demonstrated that 4D tumor tracking was feasible using existing couch with implementation of appropriate tracking methodology and with modifications in the control system.

WE-G-213CD-06: Implementation of Real-Time Tumor Tracking Using Robotic Couch.

PURPOSE: The purpose of this study was to present a novel method for real- time tumor tracking using a commercially available robotic treatment couch, and to evaluate tumor tracking accuracy. METHODS: Commercially available robotic couches are capable of positioning patients with high level of accuracy; however, currently there is no provision for compensating tumor motion using these systems. Elekta's existing commercial couch (PreciseTM Table) was used without changing its design. To establish the real-time couch motion for tracking, a novel control system was developed and implemented. The tabletop could be moved in horizontal plane (laterally and longitudinally) using two Maxon-24V motors with gearbox combination. Vertical motion was obtained using robust 70V-Rockwell Automation motor. For vertical motor position sensing, we used Model 755A-Accu- Coder encoder. Two Baumer-ITD_01_4mm shaft encoders were used for the lateral and longitudinal motions of the couch. Motors were connected to the Advance Motion Controls (AMC) amplifiers: for the vertical motion, motor AMC-20A20-INV amplifier was used, and two AMC-Z6A8 amplifiers were applied for the lateral and longitudinal couch motions. The Galil DMC-4133 controller was connected to standard PC computer using USB port. The system had two independent power supplies: Galil PSR-12- 24-12A, 24vdc power supply with diodes for controller and 24vdc motors and amplifiers, and Galil-PS300W72 72vdc power supply for vertical motion. Control algorithms were developed for position and velocity adjustment. RESULTS: The system was tested for real-time tracking in the range of 50mm in all 3 directions (superior-inferior, lateral, anterior- posterior). Accuracies were 0.15, 0.20, and 0.18mm, respectively. Repeatability of the desired motion was within ± 0.2mm. CONCLUSIONS: Experimental results of couch tracking show feasibility of real-time tumor tracking with high level of accuracy (within sub-millimeter range). This tracking technique potentially offers a simple and effective method to minimize healthy tissues irradiation.Acknowledgement: Study supported by Elekta,Ltd. Study supported by Elekta, Ltd.

SU-E-J-81: Beveled Needle Tip Detection Error in Ultrasound-Guided Prostate Brachytherapy.

PURPOSE: To quantify the needle tip detection errors in ultrasound images due to bevel-tip orientation in relation to the location on template grid. METHODS: Transrectal ultrasound (TRUS) system (BK Medical) with physical template grid and 18-gauge bevel-tip (20-deg beveled angle) brachytherapy needle (Bard Medical, Covington, GA) were used. The TRUS was set at 6.5MHz in water phantom at 40°C and measurements were taken with 50% and 100% TRUS gains. Needles were oriented with bevel-tip facing up (0-degree) and inserted through template grid-holes. Reference needle depths were measured when needle tip image intensity was bright enough for potentially consistent readings. High-resolution digital vernier caliper was used to measure needle depth. Needle bevel-tip orientation was then changed to bevel down (by rotating 180-degree) and needle depth was adjusted by retracting so that the needle-tip image intensity appeared similar to when the needle bevel-tip was at 0-degree orientation. Clinically relevant locations were considered for needle placement on the template grids (1st row to 9th row, and 'a-f' columns). RESULTS: For 50% TRUS gain, bevel tip detection errors/differences were 0.69±0.30mm (1st row) to 3.23±0.22mm (9th row) and 0.78±0.71mm (1st row) to 4.14±0.56mm (9th row) in columns 'a' and 'D', respectively. The corresponding errors for 100% TRUS gain were 0.57±0.25mm to 5.24±0.36mm and 0.84±0.30mm to 4.2±0.20mm in columns 'a' and 'D', respectively. These errors/differences varied linearly for grid-hole locations on the rows and columns in between, smaller to large depending on distance from the TRUS probe. Observed no effect of gains (50% vs. 100%) along 'D' column, which was directly above the TRUS probe. CONCLUSIONS: Experiment results revealed that the beveled needle tip orientation could significantly impact the detection accuracy of the needle tips, based on which the seeds might be delivered. These errors may lead to considerable dosimetric deviations in prostate brachytherapy seed implantation.

SU-E-T-412: Can Cyberknife SBRT Be an Alternative to Brachytherapy for Cervical Cancer Treatment?

PURPOSE: To investigate the effectiveness of stereotactic body radiation therapy (SBRT) with Cyberknife for treatment of squamous cell carcinoma (SCCa) of cervix that are commonly treated with brachytherapy. METHODS: SCCa of cervix is routinely treated with external beam radiation therapy (EBRT) followed by brachytherapy. Common practice is to use high-dose- rate (HDR) brachytherapy, mainly with Ir-192; however, low-dose-rate (LDR) brachytherapy with Cs-137 is also used. Three of our patients with cervical SCCa who were chosen to have LDR brachytherapy (Cs-137 with tandem and ovoids) could not tolerate the prolonged treatment or applicator placement. All these patients previously received 45Gy (1.8Gy/fratction) from EBRT and well tolerated. Planned LDR treatment dose and time were for patient-1: 42.63Gy in 73.5hr, patient-2: 42.34Gy in 73hr, patient-3: 41.76Gy in 72hr. Delivered LDR dose and time were: 3.75Gy in 6.5hr, OGy in Ohr, and 17.3Gy in 19.8hr, for patient-1, -2 and -3, respectively. Two of the three patients tolerated LDR treatment partially; the second patient could not tolerate the applicator, which required immediate removal after placement. Treatments were completed with Cyberknife SBRT (CK-SBRT)doses of 25Gy, 15Gy and 25Gy for patient-1, -2 and -3, respectively; all had 5Gy/fraction and 3fractions/week. Prescriptions were at 80% isododelines; CTV coverages were 96.6%, 99.9% and 100% for patient-1, -2 and -3, respectively. RESULTS: Till their last follow-up in February 2012, all three patients were doing fine clinically without any evidence of disease; none of these patients had any complications that could be related to CK-SBRT. CONCLUSIONS: Appears that CK-SBRT can be a viable treatment alternative to brachytherapy. CK-SBRT may also be more appealing to patients and physicians for a variety of reasons such as out-patient procedure, shorter treatment time, no need for operating room, and no need for applicator insertion and tolerance. However, extensive clinical study is warranted in this regard.

SU-E-T-422: Lung SBRT Using Cyberknife: Technique and Treatment Outcome.

PURPOSE: At East Carolina University, we have been treating primary and secondary lung cancers with Cyberknife stereotactic body radiotherapy (CK- SBRT) since February 2009. Till October 2011, we have treated a total of 79 patients (83 sites). In this study, we present our experience in CK-SBRT and clinical outcome of the treated patients. METHODS: Of the 79 patients, 43 were female; age of the whole patient population ranged 33.2-89.7yrs (median=73.2yrs). Patients treated for primary lung cancer (n=57) had severe chronic obstructive pulmonary disease (COPD) and were not surgical candidates. Cyberknife robotic system with tracking techniques (Synchrony=52, XsiteLung=22, XsightSpine=5) were used. Majority of the patient (n=52) had multiple gold fiducials placed (1-6 placed; 1-4 tracked per patient) either percutaneously or bronchoscopically. CT images were used for dosimetric planning, by medical physicists, using Cyberknife MultiPlan software. Prescription doses were 25Gy-55Gy in 3-5 fractions (mean=48.2Gy, median=50Gy); doses were prescribed mainly to 80% isodoseline (range=75-96%, mean=81.4%). PTV margin varied from 0-7mm (mean±SD=3.2±1.4mm), based on the tumor locations; breathing patterns and cancer type. Dosimetric coverage of GTV and PTV were (mean±SD): 97.8±5% and 94.7±6.9%, respectively. The treatment response was assessed using either a CT or a PET scan or both. RESULTS: The median follow up was 13.1months (range 0.3-31.9 months). Overall response rate was 98.8% (CR=73.5%). Local failure free survival at one year was 84% for primary (n=57), 76% for recurrent (n=16) lung cancer and 100% for metastatic (n=10) tumors. The toxicity rate was low with one patient reported to have chest wall pain and one patient developed grade 3-4 radiation pneumonitis. CONCLUSIONS: In most of the cases tight PTV margins were used. Since the prescriptions were at 80% isodeose line with more than 94% PTV coverage, the treatment outcome appeared reasonable. Further study relating PTV margin, dosimetric coverage, and treatment outcome is in progress.

A robotic approach to 4D real-time tumor tracking for radiotherapy.

Respiratory and cardiac motions induce displacement and deformation of the tumor volumes in various internal organs. To accommodate this undesired movement and other errors, physicians incorporate a large margin around the tumor to delineate the planning target volume, so that the clinical target volume receives the prescribed radiation dose under any scenario. Consequently, a large volume of healthy tissue is irradiated and sometimes it is difficult to spare critical organs adjacent to the tumor. In this study we have proposed a novel approach to the 4D active tracking and dynamic delivery incorporating the tumor motion prediction technique. This method has been applied to the two commercially available robotic treatment couches. The proposed algorithm can predict the tumor position and the robotic systems are able to continuously track the tumor during radiation dose delivery. Therefore a precise dose is given to a moving target while the dose to the nearby critical organs is reduced to improve the patient treatment outcome. The efficacy of the proposed method has been investigated by extensive computer simulation. The tumor tracking method is simulated for two couches: HexaPOD robotic couch and ELEKTA Precise Table. The comparison results have been presented in this paper. In order to assess the clinical significance, dosimetric effects of the proposed method have been analyzed.

A real-time prostate cancer detection technique using needle insertion force and patient-specific criteria during percutaneous intervention.

In this article, the authors present a novel real-time cancer detection technique by using needle insertion forces in conjunction with patient-specific criteria during percutaneous interventions. Needle insertion experiments and pathological analysis were performed for developing a computer-aided detection (CAD) model. Backward stepwise regression method was performed to identify the statistically significant patient-specific factors. A baseline force model was then developed using these significant factors. The threshold force model that estimated the lower bound of the cancerous tissue forces was formulated by adding an adjustable classifier to the baseline force model. Tradeoff between sensitivity and specificity was obtained by varying the threshold value of the classifier, from which the receiver-operating characteristic (ROC) curve was generated. Sequential quadratic programming was used to optimize the CAD model by maximizing the area under the ROC curve (AUC) using a set of model-training patient data. When the CAD model was evaluated using an independent set of model-validation patient data, an AUC of 0.90 was achieved. The feasibility of cancer detection in real time during percutaneous interventions was established.

Robotic system for prostate brachytherapy.

In contemporary brachytherapy procedures, needle placement at the desired target is challenging for a variety of reasons. A robot-assisted brachytherapy system can potentially improve needle placement and seed delivery, resulting in enhanced therapeutic outcome. In this paper we present a robotic system with 16 degrees of freedom (DOF) (9 DOF for the positioning module and 7 DOF for the surgery module) that has been developed and fabricated for prostate brachytherapy. Strategies to reduce needle deflection and target movement were incorporated after extensive experimental validation. Provision for needle motion and force feedback was included in the system to improve robot control and seed delivery. Preliminary experimental results reveal that the prototype system is sufficiently accurate in placing brachytherapy needles.

Efficacy of prostate stabilizing techniques during brachytherapy procedure.

During the prostate brachytherapy procedure, multiple needles are inserted into the prostate and radioactive seeds are deposited. Stabilizing needles are first inserted to provide some rigidity and support to the prostate, ideally this will provide better seed placement and an overall improved treatment. However, there is much speculation regarding the effectiveness of using regular brachytherapy needles as stabilizers. In this study, we explored the efficacy of (1) two types of needles--18 gauge brachytherapy needle vs. 18 gauge hooked needle; and (2) parallel vs. angulated needle configurations to stabilize the prostate. Prostate phantom movement and needle insertion progression were imaged using ultrasound (US). The recorded images were analyzed and prostate displacement was computed from images using implanted artifacts. Experimentation allowed us to further understand the mechanics behind prostate stabilization. We observed superior stabilization by the hooked needles compared to the regular brachytherapy needles (more than 40% for parallel stabilization). Prostate movement was also reduced significantly when regular brachytherapy needles were in an angulated configuration as compared to the parallel configuration (approximately 40%). When the hooked needles were angled for stabilization, further improvement in decreased displacement was observed. In general, for convenience of dosimetric planning, all needles are desired to be in parallel and in this case, hooked needles are better suited to improve stabilization of the prostate. On the other hand, both regular and hooked needles appear to be equally effective in reducing prostate movement when they are in angulated configurations, which will be useful in robotic permanent seed implantation (PSI).

Needle insertion force estimation model using procedure-specific and patient-specific criteria.

Placement accuracy of different types of surgical needles in soft biological tissues depends on a variety of factors. The needles used for prostate brachytherapy procedures are typically about 200 mm in length and 1.27-1.47 mm in diameter. These needles are prone to deflection and thereby depositing the seeds at a location other than the planned one. Thus tumorous tissues may not receive the planned dose whereas the critical organs may be over-dosed. A significant amount of needle deflection and target movement is related to some procedure-specific criteria and some patient-specific criteria. In this paper we have developed needle insertion force models taking both procedure-specific criteria and patient-specific criteria. These statistical models can be used to estimate the force that the needle will experience during insertion and thereby control the needle to reduce the needle deflection and enhance seed delivery accuracy.

In-vivo measurement of surgical needle intervention parameters: a pilot study.

Percutaneous intervention is essential in numerous medical diagnostic and therapeutic procedures. In these procedures, accurate insertion of the surgical needle is very important. But precise interstitial intervention is quite challenging. Robot-assisted needle intervention can significantly improve accuracy and consistency of various medical procedures. To design and control any robotic system, the design and control engineers must know the forces that will be encountered by the system and the motion trajectories that the needling mechanism will have to follow. Several researchers have reported needle insertion forces encountered while steering through soft tissue and soft material phantoms, but hardly any in-vivo force measurement data is available in the literature. In this paper, we present needle insertion forces and motion trajectories measured during actual brachytherapy needle insertion while implanting radioactive seeds in the prostate glands of twenty five patients.

Effects of velocity modulation during surgical needle insertion.

Precise interstitial intervention is essential for many medical diagnostic and therapeutic procedures. But accurate insertion and placement of surgical needle in soft tissue is quite challenging. The understanding of the interaction between surgical needle and soft tissue is very important to develop new devices and systems to achieve better accuracy and to deliver quality treatment. In this paper we present the effects of velocity (linear, rotational, and oscillatory) modulation on needle force and target deflection. We have experimentally verified our hypothesis that needle insertion with continuous rotation reduces target movement and needle force significantly. We have observed little changes in force and target deflection in rotational oscillation (at least at lower frequency) of the needle.