Characterisation of a Silicon Photomultiplier Based Oncological Brachytherapy Fibre Dosimeter.

Source localisation and real-time dose verification are at the forefront of medical research in brachytherapy, an oncological radiotherapy procedure based on radioactive sources implanted in the patient body. The ORIGIN project aims to respond to this medical community's need by targeting the development of a multi-point dose mapping system based on fibre sensors integrating a small volume of scintillating material into the tip and interfaced with silicon photomultipliers operated in counting mode. In this paper, a novel method for the selection of the optimal silicon photomultipliers to be used is presented, as well as a laboratory characterisation based on dosimetric figures of merit. More specifically, a technique exploiting the optical cross-talk to maintain the detector linearity in high-rate conditions is demonstrated. Lastly, it is shown that the ORIGIN system complies with the TG43-U1 protocol in high and low dose rate pre-clinical trials with actual brachytherapy sources, an essential requirement for assessing the proposed system as a dosimeter and comparing the performance of the system prototype against the ORIGIN project specifications.

Measuring nonclassicality with silicon photomultipliers.

Detector stochastic deviations from an ideal response can hamper the measurement of quantum properties of light, especially in the mesoscopic regime where photon-number resolution is required. We demonstrate that, by proper analysis of the output signal, nonclassicality of twin-beam states can be detected and exploited with commercial and cost-effective silicon-based photon-number-resolving detectors.

Mass-manufacturable scintillation-based optical fiber dosimeters for brachytherapy.

Scintillation-based fiber dosimeters are a powerful tool for minimally invasive localized real-time monitoring of the dose rate during Low Dose Rate (LDR) and High Dose Rate (HDR) brachytherapy (BT). This paper presents the design, fabrication, and characterization of such dosimeters, consisting of scintillating sensor tips attached to polymer optical fiber (POF). The sensor tips consist of inorganic scintillators, i.e. Gd2O2S:Tb for LDR-BT, and Y2O3:Eu+4YVO4:Eu for HDR-BT, dispersed in a polymer host. The shape and size of the tips are optimized using non-sequential ray tracing simulations towards maximizing the collection and coupling of the scintillation signal into the POF. They are then manufactured by means of a custom moulding process implemented on a commercial hot embossing machine, paving the way towards series production. Dosimetry experiments in water phantoms show that both the HDR-BT and LDR-BT sensors feature good consistency in the magnitude of the average photon count rate and that the photon count rate signal is not significantly affected by variations in sensor tip composition and geometry. Whilst individual calibration remains necessary, the proposed dosimeters show great potential for in-vivo dosimetry for brachytherapy.

Assessment of a Silicon-Photomultiplier-Based Platform for the Measurement of Intracellular Calcium Dynamics with Targeted Aequorin.

Ca2+ is among the most important intracellular second messengers participating in a plethora of biological processes, and the measurement of Ca2+ fluctuations is significant in the phenomenology of the underlying processes. Aequorin-based Ca2+ probes represent an invaluable tool for reliable measurement of Ca2+ concentrations and dynamics in different subcellular compartments. However, their use is limited due to the lack on the market of ready-to-use, cost-effective, and portable devices for the detection and readout of the low-intensity bioluminescence signal produced by these probes. Silicon photomultipliers (SiPMs) are rapidly evolving solid-state sensors for low light detection, with single photon sensitivity and photon number resolving capability, featuring low cost, low voltage, and compact format. Thus, they may represent the sensors of choice for the development of such devices and, more in general, of a new generation of multipurpose bioluminescence detectors suitable for cell biology studies. Ideally, a detector customized for these purposes must combine high dynamic range with high fidelity in reconstructing the light intensity signal temporal profile. In this article, the ability to perform aequorin-based intracellular Ca2+ measurements using a multipurpose, low-cost setup exploiting SiPMs as the sensors is demonstrated. SiPMs turn out to assure performances comparable to those exhibited by a custom-designed photomultiplier tube-based aequorinometer. Moreover, the flexibility of SiPM-based devices might pave the way toward routinely and wide scale application of innovative biophysical protocols.

Optimizing Silicon photomultipliers for Quantum Optics.

Silicon Photomultipliers are potentially ideal detectors for Quantum Optics and Quantum Information studies based on mesoscopic states of light. However, their non-idealities hampered their use so far. An optimal mode of operation has been developed and it is presented here, proving that this class of sensors can actually be exploited for the characterization of both classical and quantum properties of light.