Proton beam spot size and position measurements using a multi-strip ionization chamber.

PURPOSE: To develop and characterize a large-area multi-strip ionization chamber (MSIC) for efficient measurement of proton beam spot size and position at a synchrotron-based proton therapy facility. METHODS AND MATERIALS: A 420 mm x 320 mm MSIC was designed with 240 vertical strips and 180 horizontal strips at 1.75 mm pitch. The MSIC was characterized by irradiating a grid of proton spots across 17 energies from 73.5 MeV to 235 MeV and comparing to simultaneous measurements made with a reference Gafchromic EBT3 film. Beam profiles, spot sizes, and positions were analyzed. Short term measurement stability and sensitivity were evaluated. RESULTS: Excellent agreement was demonstrated between the MSIC and EBT3 film for both spot size and position measurements. Spot sizes agreed within ± 0.18 mm for all energies tested. Measured beam spot positions agreed within ± 0.17 mm. The detector showed good short term measurement stability and low noise performance. CONCLUSION: The large-area MSIC enables efficient and accurate proton beam spot characterization across the clinical energy range. The results indicate the MSIC is suitable for pencil beam scanning proton therapy commissioning and quality assurance applications requiring fast spot size and position quantification.

Verification of initial-and-final-state opacity for unambiguous weighted automata.

Initial-and-final-state opacity (IFO) is a type of opacity that characterizes a system's ability to prevent the disclosure of information about whether its evolution starts at an initial state and ends at a final state. In this paper, we extend the notion of IFO from the logical automata to the framework of unambiguous weighted automata (UWAs) that do not contain any cycle composed solely of unobservable events. For the verification of IFO, we first construct a labeled observer and a trellis-based initial state estimator for a given UWA. Even though the labeled observer has much smaller state space compared to the trellis-based initial state estimator, it cannot be used when the set of secret state pairs or the set of non-secret state pairs is not in the Cartesian product form. Based on the labeled observer, we present a more efficient method to verify IFO in the case when the set of non-secret state pairs is expressed as a Cartesian product, regardless of whether the set of secret state pairs is in the Cartesian product form. Furthermore, we use the labeled observer to verify initial-state opacity for a UWA.