Christopher W. Kennedy

High-Resolution, Small Animal Radiation Research Platform With X-Ray Tomographic Guidance Capabilities

PURPOSE To demonstrate the computed tomography, conformal irradiation, and treatment planning capabilities of a small animal radiation research platform (SARRP). METHODS AND MATERIALS The SARRP uses a dual-focal spot, constant voltage X-ray source mounted on a gantry with a source-to-isocenter distance of 35 cm. Gantry rotation is limited to 120 degrees from vertical. X-rays of 80-100 kVp from the smaller 0.4-mm focal spot are used for imaging. Both 0.4-mm and 3.0-mm focal spots operate at 225 kVp for irradiation. Robotic translate/rotate stages are used to position the animal. Cone-beam computed tomography is achieved by rotating the horizontal animal between the stationary X-ray source and a flat-panel detector. The radiation beams range from 0.5 mm in diameter to 60 x 60 mm(2). Dosimetry is measured with radiochromic films. Monte Carlo dose calculations are used for treatment planning. The combination of gantry and robotic stage motions facilitate conformal irradiation. RESULTS The SARRP spans 3 ft x 4 ft x 6 ft (width x length x height). Depending on the filtration, the isocenter dose outputs at a 1-cm depth in water were 22-375 cGy/min from the smallest to the largest radiation fields. The 20-80% dose falloff spanned 0.16 mm. Cone-beam computed tomography with 0.6 x 0.6 x 0.6 mm(3) voxel resolution was acquired with a dose of <1 cGy. Treatment planning was performed at submillimeter resolution. CONCLUSION The capability of the SARRP to deliver highly focal beams to multiple animal model systems provides new research opportunities that more realistically bridge laboratory research and clinical translation.

Robotic assistance for ultrasound-guided prostate brachytherapy

We present a robotically assisted prostate brachytherapy system and test results in training phantoms and Phase-I clinical trials. The system consists of a transrectal ultrasound (TRUS) and a spatially co-registered robot, fully integrated with an FDA-approved commercial treatment planning system. The salient feature of the system is a small parallel robot affixed to the mounting posts of the template. The robot replaces the template interchangeably, using the same coordinate system. Established clinical hardware, workflow and calibration remain intact. In all phantom experiments, we recorded the first insertion attempt without adjustment. All clinically relevant locations in the prostate were reached. Non-parallel needle trajectories were achieved. The pre-insertion transverse and rotational errors (measured with a Polaris optical tracker relative to the templates coordinate frame) were 0.25 mm (STD=0.17 mm) and 0.75 degrees (STD=0.37 degrees). In phantoms, needle tip placement errors measured in TRUS were 1.04 mm (STD=0.50mm). A Phase-I clinical feasibility and safety trial has been successfully completed with the system. We encountered needle tip positioning errors of a magnitude greater than 4mm in only 2 of 179 robotically guided needles, in contrast to manual template guidance where errors of this magnitude are much more common. Further clinical trials are necessary to determine whether the apparent benefits of the robotic assistant will lead to improvements in clinical efficacy and outcomes.

Modeling and control of the Mitsubishi PA-10 robot arm harmonic drive system

The purpose of this paper is to present our results in developing a dynamic model of the Mitsubishi PA-10 robot arm for the purpose of low-velocity trajectory tracking using low-feedback gains. The PA-10 is ideal for precise manipulation tasks because of the backdrivability, precise positioning capabilities, and zero backlash afforded by its harmonic drive transmission (HDT). However, the compliance and oscillations inherent in harmonic drive systems, and the lack of any technical information on the internal dynamics of the transmission, make the development of an accurate dynamic model of the robot extremely challenging. The novelty of this research is therefore the development of a systematic algorithm to extract the model parameters of a harmonic drive transmission in the robot arm to facilitate model-based control. We have modeled all seven joints of the Mitsubishi PA-10, and we have done several experiments to identify the various parameters of the harmonic drive system. We conclude with a sample trajectory-tracking task that demonstrates our model-based controller for the Mitsubishi PA-10 robot arm.

A Novel Approach to Robotic Cardiac Surgery Using Haptics and Vision

Cardiovascular disease is one of the leading causes of death in the United States and also a major disease nationwide. Over 700,000 coronary artery bypass graft (CABG) procedures are performed annually all around the world, of which 350,000 are performed in the United States. The use of mechanical stabilizers to isolate and immobilize the surface region of the heart is not without its limitations such as hemodynamic deterioration, and arrythmia induction requiring inotropic support. Consequently, the use of mechanical stabilizers leads to a poor immobilization of the surgical field in spite of significant forces of traction and retraction used with these devices. The primary goal of this research is to develop effective haptic (sense of touch) and visual servoing methods with the long-term goal of eliminating the need for mechanical stabilizers and extracorporeal support for CABG procedures. We present in this paper the results from our initial work in the area of tracking a deformable membrane using vision and providing haptic feedback to the user, based on the visual information through the vision hardware and the material properties of the membrane. In our first experiment, we track the deformation of a rubber membrane in real-time through stereovision while providing haptic feedback to the user interacting with the reconstructed membrane through the PHANToM haptic device. In the second experiment, we verify the ability of our vision system to track a point on a surface undergoing a complex 3D motion.

The small-animal radiation research platform (SARRP): dosimetry of a focused lens system

A small animal radiation platform equipped with on-board cone-beam CT and conformal irradiation capabilities is being constructed for translational research. To achieve highly localized dose delivery, an x-ray lens is used to focus the broad beam from a 225 kVp x-ray tube down to a beam with a full width half maximum (FWHM) of approximately 1.5 mm in the energy range 40-80 keV. Here, we report on the dosimetric characteristics of the focused beam from the x-ray lens subsystem for high-resolution dose delivery. Using the metric of the average dose within a 1.5 mm diameter area, the dose rates at a source-to-surface distance (SSD) of 34 cm are 259 and 172 cGy min(-1) at 6 mm and 2 cm depths, respectively, with an estimated uncertainty of +/-5%. The per cent depth dose is approximately 56% at 2 cm depth for a beam at 34 cm SSD.

Combining haptic and visual servoing for cardiothoracic surgery

The primary goal of this research is to develop effective haptic and visual servoing methods, with the eventual goal of eliminating the need for mechanical stabilizers in a coronary artery bypass graft procedure by presenting a stationary operative site to the surgeon performing the procedure using haptic and visual feedback. We present the results from our initial work in the area of tracking a deformable membrane using vision and providing haptic feedback to the user based on the vision information and the material properties of the membrane. In our first experiment, we track the deformation of a rubber membrane in real-time through stereo vision while providing haptic feedback to the user interacting with the reconstructed membrane through the PHANToM haptic device. In the second experiment, we verify the ability of our vision system to track a point on a surface undergoing a complex 3D motion.

Effects of the Bowman-Birk protease inhibitor on survival of fibroblasts and cancer cells exposed to radiation and cis-platinum.

The Bowman-Birk inhibitor (BBI) is a soybean-derived anticarcinogenic protease inhibitor with anti-inflammatory activity. To assess the possibility of utilizing BBI for alleviating the side effects associated with lung cancer radiation and chemotherapy, we have determined the effects of BBI and a soybean concentrate enriched in BBI (known as BBIC) on radiation- and cis-platinum-induced cytotoxicity in A549 human lung cancer cells. The results demonstrated that neither BBI nor BBIC protected A549 cells from radiation- and cis-platinum-induced cytotoxicity. In fact, BBI and BBIC potentiated the cell-killing effects induced by cis-platinum alone, and BBIC treatment led to significantly enhanced cell killing by cis-platinum in combination with radiation treatment in the lung carcinoma cells. BBI conferred a significant protective effect onto mouse fibroblasts (10T1/2 cells) treated with cis-platinum in combination with 6 Gy of X-ray irradiation. These results suggest that BBI and BBIC, when given to lung cancer patients, are unlikely to interfere with cancer treatment utilizing radiation and cis-platinum.

Small animal radiation research platform: imaging, mechanics, control and calibration

In cancer research, well characterized small animal models of human cancer, such as transgenic mice, have greatly accelerated the pace of development of cancer treatments. The goal of the Small Animal Radiation Research Platform (SARRP) is to make those same models available for the development and evaluation of novel radiation therapies. In combination with advanced imaging methods, small animal research allows detailed study of biological processes, disease progression, and response to therapy, with the potential to provide a natural bridge to the clinical environment. The SARRP will realistically model human radiation treatment methods in standard animal models. In this paper, we describe the mechanical and control structure of the system. This system requires accurate calibration of the x-ray beam for both imaging and radiation treatment, which is presented in detail in the paper.

Robotic assistance for ultrasound guided prostate brachytherapy

We present a robotically assisted prostate brachytherapy system and test results in training phantoms. The system consists of a transrectal ultrasound (TRUS) and a spatially co-registered robot integrated with an FDA-approved commercial treatment planning system. The salient feature of the system is a small parallel robot affixed to the mounting posts of the template. The robot replaces the template interchangeably and uses the same coordinate system. Established clinical hardware, workflow and calibration are left intact. In these experiments, we recorded the first insertion attempt without adjustment. All clinically relevant locations were reached. Non-parallel needle trajectories were achieved. The pre-insertion transverse and rotational errors (measured with Polaris optical tracker relative to the templates coordinate frame) were 0.25mm (STD = 0.17mm) and 0.75 degrees (STD = 0.37 degrees). The needle tip placement errors measured in TRUS were 1.04mm (STD = 0.50mm). The system is in Phase-I clinical feasibility and safety trials, under Institutional Review Board approval.

Estimation and modeling of the harmonic drive transmission in the Mitsubishi PA-10 robot arm

The purpose of this paper is to present our results in developing a dynamic model of the Mitsubishi PA-10 robot arm for the purpose of low velocity trajectory tracking using very low feedback gains. The novelty of this research is therefore the development of a systematic algorithm to extract the model parameters of a harmonic drive transmission in the robot arm to facilitate model-based control. We have chosen the elbow pitch joint (joint 4) of the PA-10 robot arm for estimation and modeling purposes. We have done several experiments to identify the various parameters of the harmonic drive system. We conclude with a sample trajectory tracking task whereby the feedback torque required to do trajectory tracking with and without the parameter identification of the HDT is significantly different.