Radiation Oncology

A new unified motion planning algorithm for autonomous Underwater Vehicle-Manipulator Systems (UVMS) has been presented in this paper. Commonly, a UVMS consists of two sub-systems, a vehicle and a manipulator, having vastly different dynamic responses. The proposed algorithm considers the variability in dynamic bandwidth of the complex UVMS system and generates not only kinematically admissible but also dynamically feasible reference trajectories. Additionally, this motion planning algorithm exploits the inherent kinematic redundancy of the whole system and provides reference trajectories that accommodates other important criteria such as thruster/actuator faults and saturations, and also minimizes hydrodynamic drag. Effectiveness of the proposed unified motion planning algorithm has been verified by extensive computer simulation. The results are quite promising.

A new motion coordination algorithm for an autonomous underwater vehicle-manipulator system (UVMS) is proposed. This algorithm generates the desired trajectories for both the vehicle and the manipulator in such a way that the total hydrodynamic drag on the system is minimized. Resolution of kinematic redundancy of the system is performed at the acceleration level so that this algorithm can be incorporated into the system dynamics. The dynamics of the UVMS are modeled using a quasi-Lagrange approach. A state-space formulation of the system along with a model-based controller design for trajectory-following tasks that includes thruster dynamics is also presented. The computer simulation results demonstrate the effectiveness of this proposed method in reducing the drag on the system.

In prostate brachytherapy, seeds can detach from their deposited sites and move locally in the pelvis or migrate to distant sites including the pulmonary and cardiac regions. Undesirable consequences of seed migration include inadequate dose coverage of the prostate and tissue irradiation effects at the site of migration. Thus, it is clinically important to develop seed immobilization techniques. Methods: We first analyze the possible causes for seed movement, and propose three potential techniques for seed immobilization: (1) surgical glue, (2) laser coagulation and (3) diathermy coagulation. The feasibility of each method is explored. Experiments were carried out using fresh bovine livers to investigate the efficacy of seed immobilization using surgical glue. Results: Results have shown that the surgical glue can effectively immobilize the seeds. Evaluation of the radiation dose distribution revealed that the non-immobilized seed movement would change the planned isodose distribution considerably; while by using surgical glue method to immobilize the seeds, the changes were negligible. Conclusions: Prostate brachytherapy seed immobilization is necessary and three alternative mechanisms are promising for addressing this issue. Experiments for exploring the efficacy of the other two proposed methods are ongoing. Devices compatible with the brachytherapy procedure will be designed in future.

rotation along any of two axes (x and z) with vertical (y) rotation eliminated by couch adjustment. Rotation was denominated around an axis passing through the isocenter and lying 45 in the xz plane. Imaging features were distributed at locations that modeled clinical landmark choice: symmetries guided landmark position within an imaging plane but not all locations were assumed available; fiducials were placed near the tumor center as viewed in the horizontal plane, but vertical depth could be limited. The conditions model fiducials introduced alongside a hollow lumen (e.g., bronchus) about which the tumor is eccentrically situated. Euler's transformation equations determined the displacement of the landmarks resulting from a rotation of the treatment frame that leaves the isocenter position fixed. Results: Landmarks placed at (x,z) positions of (4,2), (-2,-4), (1,-1) (cm units) and a y-depth of 8 all shifted with a 3 rotation by Dx =-0.295, Dy =-0.085, Dz = +0.295, which would produce isocenter shift errors of the same magnitude were the couch translated to bring the landmarks into apparent alignment with the reference frame. If a fourth landmark were placed in the remaining (-x,+z) quadrant of the reference frame with coordinates (-1,1), its shifts would be Dx =-0.297 Dy = +0.063, Dz +0.297. An incorrect couch translation now of 3mm in x and z, and 0.01 in y brings the landmarks into alignment to within 0.75mm along each projected axis. The residual landmark misalignments lay below an action threshold of 1mm despite isocenter coordinate shift errors of 3mm. Conclusions: Incomplete information at the time of image guidance may prompt erroneous isocenter shifts not detectable as actionable landmark misalignments. For nearly spherical tumor geometries, and an isocenter set initially correctly, image guidance may be the cause of tumor miss rather than its corrective. If a sufficiently large set of fiducials cannot be identified symmetrically about isocenter, additional (bony) landmarks should be included to validate shifts.

Background: It is known that lung cancer incidence and mortality rate are higher in African Americans (AA) than whites. In Eastern North Carolina, there is a higher percentage of AA population than the national average (30.2% vs. 12.4%) and a higher incidence of lung cancer in this region. We investigated demography and survival of lung cancer patients diagnosed and treated in a single institution. Methods: The study includes 2351 patients diagnosed with lung cancer between 2001 and 2010 at East Carolina University. AA and whites were compared by age, sex, race, stage, histology, smoking history and insurance information using chi-square analyses. Patient survival was modeled using Cox proportional hazards regression (SAS version 9.2). Results: The distribution of lung cancer was 70% in whites and 30% in AA. The proportion of AA and whites differed significantly for age, sex, histology, stage, and insurance. Patients aged >70 (p < 0.0001) and 51-70 (p = 0.0064) died sooner than those ≤50 years old. Compared with squamous cell, SCLC had inferior survival (HR = 2.0, 95%CI = 1.7-2.3). Privately insured patients survived longer than those with medicare (p < 0.0001), medicaid (p = 0.0009), or no insurance (p < 0.0001). The survival disadvantage for medicaid (p = 0.0076) and no insurance (p = 0.0033) persisted on multivariable analysis. Race was not a significant predictor of survival on multivariable analysis (p = 0.66). Conclusion: This is one of the largest lung cancer patient populations from a single institution showing demographic differences between the two races with similar survival outcome. Age, histology and type of insurance were strong predictors of survival outcome. Older age, small cell histology and medicaid and no insurance had significantly shorter overall survival.

This study presents a polyacrylamide gel as a phantom material for needle insertion studies specifically developed for self-actuating needles to enhance the precise placement of needles in prostate. Bending of these self-actuating needles within tissue is achieved by Nitinol actuators attached to the needle body; however these actuators usually involve heating that can thermally damage the tissue surrounding the needles. Therefore, to develop and access feasibility of these needles, a polyacrylamide gel has been developed that mimics the thermal damage and mechanical properties of prostate tissue. Mechanical properties of the polyacrylamide gel was controlled by varying the concentrations of acrylamide monomer and N,N-methylene-bisacrylamide (BIS) cross-linker, and thermal sensitivity was achieved by adding bovine serum albumin (BSA) protein. Two polyacrylamide gels with different concentrations were developed to mimic the elastic modulus of the tissue. The two phantoms showed different rupture toughness and different deflection of bevel-tip needle. To study the thermal damage, a Nitinol wire was embedded in the phantom and resistively heated. The measured opaque zone (0.40 mm) formed around the wire was close to the estimated damage zone (0.43 mm) determined using the cumulative equivalent minutes at 43 • C.

A new technique called "curvilinear approach" for prostate seed implantation has been proposed. The purpose of this study is to evaluate the dosimetric benefit of curvilinear distribution of seeds for low-dose-rate (LDR) prostate brachytherapy. Methods: Twenty LDR prostate brachytherapy cases planned intraoperatively with VariSeed planning system and I-125 seeds were randomly selected as reference rectilinear cases. All the cases were replanned by using curved-needle approach keeping the same individual source strength and the volume receiving 100% of prescribed dose 145 Gy (V 100). Parameters such as number of needles, seeds, and the dose coverage of the prostate (D 90 , V 150 , V 200), urethra (D 30 , D 10) and rectum (D 5 , V 100) were compared for the rectilinear and the curvilinear methods. Statistical significance was assessed using two-tailed student's t-test. Results: Reduction of the required number of needles and seeds in curvilinear method were 30.5% (p < 0.001) and 11.8% (p < 0.49), respectively. Dose to the urethra was reduced significantly; D 30 reduced by 10.1% (p < 0.01) and D 10 reduced by 9.9% (p < 0.02). Reduction in rectum dose D 5 was 18.5% (p < 0.03) and V 100 was also reduced from 0.93 cc in rectilinear to 0.21 cc in curvilinear (p < 0.001). Also the V 150 and V 200 coverage of prostate reduced by 18.8% (p < 0.01) and 33.9% (p < 0.001), respectively. Conclusions: Significant improvement in the relevant dosimetric parameters was observed in curvilinear needle approach. Prostate dose homogeneity (V 150 , V 200) improved while urethral dose was reduced, which might potentially result in better treatment outcome. Reduction in rectal dose could potentially reduce rectal toxicity and complications. Reduction in number of needles would minimize edema and thereby could improve postimplant urinary incontinence. This study indicates that the curvilinear implantation approach is dosimetrically superior to conventional rectilinear implantation technique. V

Purpose: Recently, several robotic systems have been developed to perform accurate and consistent image-guided brachytherapy. Before introducing a new device into clinical operations, it is important to assess the reliability and mean time before failure ͑MTBF͒ of the system. In this article, the authors present the preclinical evaluation and analysis of the reliability and MTBF of an autonomous robotic system, which is developed for prostate seed implantation. Methods: The authors have considered three steps that are important in reliability growth analysis. These steps are: Identification and isolation of failures, classification of failures, and trend analysis. For any one-of-a-kind product, the reliability enhancement is accomplished through test-fix-test. The authors have used failure mode and effect analysis for collection and analysis of reliability data by identifying and categorizing the failure modes. Failures were classified according to severity. Failures that occurred during the operation of this robotic system were considered as nonhomogenous Poisson process. The failure occurrence trend was analyzed using Laplace test. For analyzing and predicting reliability growth, commonly used and widely accepted models, Duane's model and the Army Material Systems Analysis Activity, i.e., Crow's model, were applied. The MTBF was used as an important measure for assessing the system's reliability. Results: During preclinical testing, 3196 seeds ͑in 53 test cases͒ were deposited autonomously by the robot and 14 critical failures were encountered. The majority of the failures occurred during the first few cases. The distribution of failures followed Duane's postulation as well as Crow's postulation of reliability growth. The Laplace test index was Ϫ3.82 ͑Ͻ0͒, indicating a significant trend in failure data, and the failure intervals lengthened gradually. The continuous increase in the failure occurrence interval suggested a trend toward improved reliability. The MTBF was 592 seeds, which implied that several prostate seed implantation cases would be possible without encountering any critical failure. The shape parameter for the MTBF was 0.3859 ͑Ͻ1͒, suggesting a positive reliability growth of this robotic system. At 95% confidence, the reliability for deposition of 65 seeds was more than 90%. Conclusions: Analyses of failure mode strongly indicated a gradual improvement of reliability of this autonomous robotic system. High MTBF implied that several prostate seed implant cases would be possible without encountering any critical failure.

A novel approach to the allocation of thruster forces of an autonomous underwater vehicle (AUV) is investigated. Generally, the number of thrusters in an AUV is more than what is minimally required to produce the desired motion. We investigate how to exploit the excess number of thrusters to accommodate thruster faults during operation. First, a redundancy resolution scheme is presented that takes into account the presence of excess number of thrusters along with any thruster faults and determines the reference thruster forces to produce the desired motion. These reference thruster forces are utilized in the controller to generate the required motion. This approach resolves the thruster redundancy in the Cartesian space and allows the AUV to track the task-space trajectories with asymptotic reduction of the task-space errors. Results from computer simulations are presented to demonstrate the viability of the proposed scheme.

Background Tissue-mimicking phantoms are essential for understanding the mechanics of needle-tissue interactions. Recent developments in active needles, especially for prostate brachytherapy, involve self actuation of the needle using actuators placed on the body of the needle, where actuation forces is generated by resistively heating shape memory alloy wires with electric current [1]. Therefore, the phantom materials should be able to mimic both the mechanical and thermal properties of the real tissue. Polyacrylamide (PA) gels, apart from meeting these requirements, can simulate the tissue damage from excessive heating by adding proteins to the tissue [2]. As an initial step, this work will synthesize PA gels that mimic the prostate tissue and then study the mechanical properties of these gels. Mechanical properties of the PA gels were determined by unconstrained compression and indentation tests.

Active needles are recently being developed to improve steerability and placement accuracy for various medical applications. These active needles can bend during insertion by actuators attached to their bodies. The bending of active needles enables them to be steered away from the critical organs on the way to target and accurately reach target locations previously unachievable with conventional rigid needles. These active needles combined with an asymmetric bevel-tip can further improve their steerability. To optimize the design and to develop accurate path planning and control algorithms, there is a need to develop a tissue-needle interaction model. This work presents an energy-based model that predicts needle deflection of active bevel-tipped needles when inserted into the tissue. This current model was based on an existing energy-based model for bevel-tipped needles, to which work of actuation was included in calculating the system energy. The developed model was validated with needle insertion experiments with a phantom material. The model predicts needle deflection reasonably for higher diameter needles (11.6% error), whereas largest error was observed for the smallest needle diameter (24.7% error).

Estimation of the system parameters, given noisy input/output data, is a major field in control and signal processing. Many different estimation methods have been proposed in recent years. Among various methods, Extended Kalman Filtering (EKF) is very useful for estimating the parameters of a nonlinear and time-varying system. Moreover, it can remove the effects of noises to achieve significantly improved results. Our task here is to estimate the coefficients in a spring-beam-damper needle steering model. This kind of spring-damper model has been adopted by many researchers in studying the tissue deformation. One difficulty in using such model is to estimate the spring and damper coefficients. Here, we proposed an online parameter estimator using EKF to solve this problem. The detailed design is presented in this paper. Computer simulations and physical experiments have revealed that the simulator can estimate the parameters accurately with fast convergent speed and improve the model efficacy.

Stereotactic body radiation therapy (SBRT) is an emerging technology for the treatment of spinal metastases, although the dosimetric impact of the calculation method on spinal dose distribution is unknown. This study attempts to determine whether CyberKnife (CK)-based SBRT using a Ray Tracing (RyTc) algorithm is comparable dosimetrically to that of Monte Carlo (MC) for thoracic spinal lesions. Our institutional CK-based SBRT database for thoracic spinal lesions was queried and a cohort was generated. Patients were planned using RyTc and MC algorithms using the same beam angles and monitor units. Dose-volume histograms of the planning target volume (PTV), spinal cord, esophagus, and skin were generated, and dosimetric parameters were compared. There were 37 patients in the cohort. The average percentage volume of PTV covered by the prescribed dose with RyTc and MC algorithms was 91.1% and 80.4%, respectively (P &lt; .001). The difference in average maximum spinal cord dose between Ry...

Modular software design is a technique that increase reusability and portability of software composed from separate parts, called modules. We have designed and developed a reusable integrated software solution for robotic prostate brachytherapy procedure. The application is capable of concurrent handling of all aspects of the image-guided brachytherapy procedure: ultrasound image acquisition, anatomic delineation, target modeling, dosimetry planning and analysis, seed delivery, and visualization of all surgerical steps involved in the procedure. Based on force feedback and visual feedback, the control module of the application is capable of controlling the robotic system (i.e. motions of the ultrasound probe and the needles), supervising the flow of the procedure via built-in strategies for emergency handling and recovery, collision avoidance, manual takeover (if necessary), needle tracking and real-time dose updates. The implementation of the developed software solution to the two brachytherapy robotic systems has been presented.

Respiratory and cardiac motions induce displacement and deformation of the tumor-volume in various internal organs. To accommodate this undesired movement and other errors, physicians incorporate a large margin around the tumor to delineate Planning Target Volume (PTV), so that the Clinical Target Volume (CTV) 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 4D Active Tracking and Dynamic Delivery (ATDD) together with tumor motion prediction. Proposed algorithm can predict tumor position and the robotic system can continuously track the tumor during radiation dose delivery, so that a precise dose is given to a moving target while reducing dose to nearby critical organs for improved patient treatment outcome. The efficacy of the proposed method has been investigated by extensive computer simulation. The results have been presented in this article.

Tumors in thorax region incur significant amount of motion and deformation due to respiratory and cardiac cycles. To accommodate this undesired movement, physicians incorporate a large standard margin around the tumor to delineate a Planning Target Volume (PTV), so that the Clinical Target Volume (CTV) receives the prescribed dose under any scenario. Consequently, a large volume of healthy tissue might be irradiated and sometimes it is difficult to spare critical organs adjacent to the tumor. For compensating this tumor motion, techniques such as breath-hold, gating, and Active Tracking and Dynamic Delivery (ATDD) are used. Although, ATDD is the most effective technique, it is the most challenging one. The ATDD can be accomplished in three different ways: adjusting the Multi-Leaf Collimator (MLC), adjusting the couch, and adjusting the MLC and couch simultaneously. The first two techniques have been explored and/or implemented in practice. However, the third approach has not been investigated extensively. In this study, we have proposed a novel approach for ATDD that exploits the advantages of both the MLC (or MLC-bank) and the HexaPOD TM robotic couch. In our proposed new approach, we have decomposed and allocated the tumor motion trajectory to the subsystems (MLC or MLC-bank and HexaPOD TM robotic couch) based on their natural frequency domains using wavelet technique. The efficacy of the proposed method has been investigated by extensive computer simulation and the results are presented in this paper.