A robustness check procedure for hypofractionated Gamma Knife radiosurgery

OBJECTIVEInterfractional residual patient shifts are often observed during the delivery of hypofractionated brain radiosurgery. In this study, the authors developed a robustness treatment planning check procedure to assess the dosimetric effects of residual target shifts on hypofractionated Gamma Knife radiosurgery (GKRS).METHODSThe residual patient shifts were determined during the simulation process immediately after patient immobilization. To mimic incorporation of residual target shifts during treatment delivery, a quality assurance procedure was developed to sample and shift individual shots according to the residual uncertainties in the prescribed treatment plan. This procedure was tested and demonstrated for 10 hypofractionated GKRS cases.RESULTSThe maximum residual target shifts were less than 1 mm for the studied cases. When incorporating such shifts, the target coverage varied by 1.9% ± 2.2% (range 0.0%–7.1%) and selectivity varied by 3.6% ± 2.5% (range 1.1%–9.3%). Furthermore, when incorporating extra random shifts on the order of 0.5 mm, the target coverage decreased by as much as 7%, and nonisocentric variation in the dose distributions was noted for the studied cases.CONCLUSIONSA pretreatment robustness check procedure was developed and demonstrated for hypofractionated GKRS. Further studies are underway to implement this procedure to assess maximum tolerance levels for individual patient cases.

The United Auto Workers’ Attempts to Unionize Volkswagen Chattanooga

The author examines attempts by the United Auto Workers (UAW) to unionize the Volkswagen (VW) plant in Chattanooga, Tennessee. These efforts were a pivotal test of labor’s ability to organize in the South. The UAW failed to organize the entire plant, despite an amenable employer, because of heavy intervention by external actors, the union’s failure to develop community support, and a paragraph in the pre-election agreement that promised wage restraint. VW management’s fear of losing state subsidies and their desire to not alienate the local business and political establishment took the card-check procedure for recognition off the table. VW management’s adoption of an accommodating position toward unionization for the entire plant, but resistance to it for the small skilled-mechanics unit, suggests that the company was willing to accept unionization only as a means to the end of creating a works council rather than out of a commitment to collective bargaining as a practice.

Supporting locomotive functions of a six-legged walking robot

Supporting locomotive functions of a six-legged walking robotThis paper presents a method for building a foothold selection module as well as methods for the stability check for a multi-legged walking robot. The foothold selection decision maker is shaped automatically, without expert knowledge. The robot learns how to select appropriate footholds by walking on rough terrain or by testing ground primitives. The gathered knowledge is then used to find a relation between slippages and the obtained local shape of the terrain, which is further employed to assess potential footholds. A new approach to function approximation is proposed. It uses the least-squares fitting method, the Kolmogorov theorem and population-based optimization algorithms. A strategy for re-learning is proposed. The role of the decision support unit in the control system of the robot is presented. The importance of the stability check procedure is shown. A method of finding the stability region is described. Further improvements in the stability check procedure due to taking into account kinematic correction are reported. A description of the system for calculating static stability on-line is given. Methods for measuring stance forces are described. The measurement of stance forces facilitates the extended stability check procedure. The correctness of the method is proved by results obtained in a real environment on a real robot.