Cascading Macrocycle and Helix Motions in a Foldarotaxane Molecular Shuttle.

The design of a dynamically assembled foldarotaxane was envisioned with the aim of operating as a two cascading triggers-based molecular shuttle. In acidic conditions, both the macrocycle and helix were localized around their respective best molecular stations because they are far enough from each other not to alter the stability of complexes. The pH-dependent localization of the macrocycle along the encircled axle allowed us to modulate the association between the helical foldamer and its sites of interaction on the axle. Under kinetic control, at low concentration and room temperature, when the foldarotaxane supramolecular architecture is kinetically stable, the pH-responsive translation of the macrocycle along the thread triggered the gliding of the helix away from its initial best station. At higher concentration, when helix assembly/disassembly process is accelerated, the system reached the equilibrium state. A new foldarotaxane isomer then appeared through the change of the relative position of the helix and macrocycle along the thread. In this isomer, the helix segregated the macrocycle away from its best station. The fine control of the kinetic and thermodynamic processes, combined with the control of pH, allowed the reciprocal segregation of the helix or the ring away from their respective best sites of interaction.

Tumor tracking and motion compensation with an adaptive tumor tracking system (ATTS): system description and prototype testing.

A novel system for real-time tumor tracking and motion compensation with a robotic HexaPOD treatment couch is described. The approach is based on continuous tracking of the tumor motion in portal images without implanted fiducial markers, using the therapeutic megavoltage beam, and tracking of abdominal breathing motion with optical markers. Based on the two independently acquired data sets the table movements for motion compensation are calculated. The principle of operation of the entire prototype system is detailed first. In the second part the performance of the HexaPOD couch was investigated with a robotic four-dimensional-phantom capable of simulating real patient tumor trajectories in three-dimensional space. The performance and limitations of the HexaPOD table and the control system were characterized in terms of its dynamic behavior. The maximum speed and acceleration of the HexaPOD were 8 mm/s and 34.5 mm/s2 in the lateral direction, and 9.5 mm/s and 29.5 mm/s2 in longitudinal and anterior-posterior direction, respectively. Base line drifts of the mean tumor position of realistic lung tumor trajectories could be fully compensated. For continuous tumor tracking and motion compensation a reduction of tumor motion up to 68% of the original amplitude was achieved. In conclusion, this study demonstrated that it is technically feasible to compensate breathing induced tumor motion in the lung with the adaptive tumor tracking system.