The Pencil Beam Scanning (PBS) technique in proton therapy uses fast magnets to scan the tumor volume rapidly. Changing the proton energy allows changing to layers in the third dimension, hence scanning the same volume several times. The PBS approach permits adapting the speed and/or current to modulate the delivered dose. We built a simple prototype that measures the dose distribution in a single step. The active detection material consists of a single layer of scintillating fibers (i.e., 1D) with an active length of 100 mm, a width of 18.25 mm, and an insignificant space (20 μm) between them. A commercial CMOS-based camera detects the scintillation light. Short exposure times allow running the camera at high frame rates, thus, monitoring the beam motion. A simple image processing method extracts the dose information from each fiber of the array. The prototype would allow scaling the concept to multiple layers read out by the same camera, such that the costs do not scale with the dimensions of the fiber array. Presented here are the characteristics of the prototype, studied under two modalities: spatial resolution, linearity, and energy dependence, characterized at the Center for Proton Therapy (Paul Scherrer Institute); the dose rate response, measured at an electron accelerator (Swiss Federal Institute of Metrology).

We present proof-of-principle results on terahertz wavefront shaping by means of a deformable mirror (DM). The DM is based on a reflective gold-coated steel membrane pushed by 35 powerful stepper actuators to enable a surface deformation of up to 1 mm out of equilibrium. The maximum excursion is equivalent to 10 wavelengths of the terahertz source centered at 3 THz and, thus, offers excellent opportunities for shaping the terahertz wavefront and beam intensity profile. As a proof of principle, we demonstrate terahertz focal spot optimization towards the diffraction limit, focal depth shifting, and terahertz imaging application. The large aperture DM offers new opportunities for the wavefront manipulation demanded by high-field terahertz science. The extreme excursion range of the DM will be beneficial for beam shaping at other wavelengths, such as visible and UV.