There are several general recommendations for quality assurance (QA) measures, which have to be performed at proton therapy centres. However, almost each centre uses a different therapy system. In particular, there is no standard procedure for centres employing pencil beam scanning and each centre applies a specific QA program. Gantry 2 is an operating therapy system which was developed at PSI and relies on the most advanced technological innovations. We developed a comprehensive daily QA program in order to verify the main beam characteristics to assure the functionality of the therapy delivery system and the patient safety system. The daily QA program entails new hardware and software solutions for a highly efficient clinical operation. In this paper, we describe a dosimetric phantom used for verifying the most critical beam parameters and the software architecture developed for a fully automated QA procedure. The connection between our QA software and the database allows us to store the data collected on a daily basis and use it for trend analysis over longer periods of time. All the data presented here have been collected during a time span of over two years, since the beginning of the Gantry 2 clinical operation in 2013. Our procedure operates in a stable way and delivers the expected beam quality. The daily QA program takes only 20 min. At the same time, the comprehensive approach allows us to avoid most of the weekly and monthly QA checks and increases the clinical beam availability.

Proton therapy, especially in the form of pencil beam scanning (PBS), allows for the delivery of highly conformal dose distributions for complex tumor geometries. However, due to scattering of protons inside the patient, lateral dose gradients cannot be arbitrarily steep, which is of importance in cases with organs at risk (OARs) in close proximity to, or overlapping with, planning target volumes (PTVs). In the PBS approach, physical pencil beams are planned using a regular grid orthogonal to the beam direction. In this work, we propose an alternative to this commonly used approach where pencil beams are placed on an irregular grid along concentric paths based on the target contour. Contour driven pencil beam placement is expected to improve dose confirmation by allowing the optimizer to best enhance the penumbra of irregularly shaped targets using edge enhancement. Its effectiveness has been shown to improve dose confirmation to the target volume and reduce doses to OARs in head-and-neck planning studies. Furthermore, the deliverability of such plans, as well as the dosimetric improvements over conventional grid-based plans, have been confirmed in first phantom based verifications.

Hollow reduced-symmetry resonant plasmonic nanostructures possess pronounced tunable optical resonances in the UV-vis-IR range, being a promising platform for advanced nanophotonic devices. However, the present fabrication approaches require several consecutive technological steps to produce such nanostructures, making their large-scale fabrication rather time-consuming and expensive. Here, we report on direct single-step fabrication of large-scale arrays of hollow parabolic- and cone-shaped nanovoids in silver and gold thin films, using single-pulse femtosecond nanoablation at high repetition rates. The lateral and vertical size of such nanovoids was found to be laser energy-tunable. Resonant light scattering from individual nanovoids was observed in the visible spectral range, using dark-field confocal microspectroscopy, with the size-dependent resonant peak positions. These colored geometric resonances in far-field scattering were related to excitation and interference of transverse surface plasmon modes in nanovoid shells. Plasmon-mediated electromagnetic field enhancement near the nanovoids was evaluated via finite-difference time-domain calculations for their model shapes simulated by three-dimensional molecular dynamics, and experimentally verified by means of photoluminescence microscopy and Raman spectroscopy.

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