Search

Stereotactic radiosurgery delivers radiation with great spatial accuracy. To achieve sub-millimeter accuracy for intracranial SRS, a head ring is rigidly fixated to the skull to create a fixed reference. For some patients, the invasiveness of the ring can be highly uncomfortable and not well tolerated. In addition, placing and removing the ring requires special expertise from a neurosurgeon, and patient setup time for SRS can often be long. To reduce the invasiveness, hardware limitations and setup time, we are developing a system for performing accurate head positioning without the use of a head ring. The proposed method uses real-time 6D optical position feedback for turning on and off the treatment beam (gating) and guiding a motor-controlled 3D head motion compensation stage. The setup consists of a central control computer, an optical patient motion tracking system and a 3D motion compensation stage attached to the front of the LINAC couch. A styrofoam head cast was custom-built for patient support and was mounted on the compensation stage. The motion feedback of the markers was processed by the control computer, and the resulting motion of the target was calculated using a rigid body model. If the target deviated beyond a preset position of 0.2 mm, an automatic position correction was performed with stepper motors to adjust the head position via the couch mount motion platform. In the event the target deviated more than 1 mm, a safety relay switch was activated and the treatment beam was turned off. The feasibility of the concept was tested using five healthy volunteers. Head motion data were acquired with and without the use of motion compensation over treatment times of 15 min. On average, test subjects exceeded the 0.5 mm tolerance 86% of the time and the 1.0 mm tolerance 45% of the time without motion correction. With correction, this percentage was reduced to 5% and 2% for the 0.5 mm and 1.0 mm tolerances, respectively. [ABSTRACT FROM AUTHOR]

The structural, electronic, vibrational, and superconducting properties of alkali (K, Rb) and alkaline earth (Ca, Sr) metal-covered monolayer graphene have been investigated based on first-principles methods. We noticed that the different adatoms and their concentrations allow tuning of the electronic properties of carbon sheets, inducing the transition from semimetallic pristine graphene to metallic decorated graphene. Moreover, the phonon calculations confirm the dynamic stability of all systems studied, while the electron–phonon coupling calculations predict that the superconducting critical temperature of CaC8 can reach the highest value of 1.86 K. Our work shows the possibility of inducing and studying superconductivity in other metal-covered 2D materials. [ABSTRACT FROM AUTHOR]