Proc. SPIE. 10058, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVII
KEYWORDS: Breast cancer, Radiation dosimetry, Scintillators, Optical fibers, Polymethylmethacrylate, Tumors, Signal to noise ratio, High dynamic range imaging, In vivo imaging, Computed tomography, Fiber optics, Silicon photomultipliers, Radiotherapy, Prostate cancer, Iridium, Gamma radiation
Brachytherapy is a radiotherapy modality where the radioactive material is placed close to the tumor, being a common treatment for skin, breast, gynecological and prostate cancers. These treatments can be of low-dose-rate, using isotopes with mean energy of 30 keV, or high-dose-rate, using isotopes such as <sup>192</sup>Ir with a mean energy of 380 keV. Currently these treatments are performed in most cases without in-vivo dosimetry for quality control and quality assurance.<p> </p>We developed a dosimeter using small diameter probes that can be inserted into the patient's body using standard brachytherapy needles. By performing real-time dosimetry in breast and prostate brachytherapy it will be possible to perform real-time dose correction when deviations from the treatment plan are observed.<p> </p>The dosimeter presented in this work was evaluated in-vitro. The studies consisted in the characterization of the dosimeter with 500 <i>μ</i>m diameter sensitive probes (with a BCF-12 scintillating optical fiber) using an inhouse made gelatin breast phantom with a volume of 566 cm<sup>3</sup>. A breast brachytherapy treatment was simulated considering a tumor volume of 27 cm<sup>3</sup> and a prescribed absolute dose of 5 Gy. The dose distribution was determined by the Inverse Planning Simulated Annealing (IPSA) optimization algorithm (ELEKTA).<p> </p>The dwell times estimated from the experimental measurements are in agreement with the prescribed dwell times, with relative error below 3%. The measured signal-to-noise ratio (SNR) including the <i>stem-effect </i>contribution is below 3%.
A small dimension, real-time readout dosimeter is desirable for specific applications in medical physics as for example, dose measurement in prostate brachytherapy. This particular radiotherapy procedure consists in the permanent deposition of low energy, low-dose and low-dose rate small sized radioactive seeds. We developed a scintillating fiber optic based dosimeter suitable for in-vivo, real-time low dose and low dose rate measurements. Due to the low scintillation light produced in the scintillating fiber, a high sensitive and high gain light detector is required. The Silicon Photomultipliers are an interesting option that allowed us to obtain good results in our studies.
In small diameter positron emission tomography (PET) systems, the determination of the depth-of-interaction (DOI) of 511 keV gamma photons in scintillator crystals is of great importance, in order to achieve high DOI resolution with good uniformity within the entire field-of-view. In this work, we propose a new method for DOI determination, in which a single layer of LYSO crystals is read out on both ends through the use of silicon photomultipliers (SiPMs), but using wavelength-shifting fibers and a reduced number of SiPMs on one end. This design results in a simpler and less expensive readout when compared to the typical dual-ended readout method, which requires two photodetectors per crystal and corresponding readout electronics. GATE simulation of the system was carried out and experimental proof-of-concept studies were performed on a single detector cell (composed of two LYSO crystals operating in coincidence), to evaluate the amount of light detected on each side of the crystal and the achievable DOI resolution with this method, taking into account the attenuation of the light signal on the fiber side with crystal-SiPM distance. The feasibility of applying this new method in full detector rings for a small animal PET system is evaluated and discussed, considering different alternatives for position readout electronics.
By means of pulsed laser spectroscopy applied to muonic hydrogen (μ¯p) we havemeasured the 2S (F=1)/(1/2) - 2P(F=2)/(3/2) transition frequency to be 49881.88(76)GHz.<sup>1</sup> By comparing this measurement with its theoretical prediction
<sup>2-7</sup> based on bound-state QED we have determined a proton radius value of r<sub>P</sub> =0.84184(67) fm. This new value
differs by 5.0 standard deviations from the CODATA value of 0.8768(69) fm,<sup>8</sup> and 3 standard deviation from the
e-p scattering results of 0.897(18) fm.<sup>9</sup> The observed discrepancy may arise from a computational mistake of
the energy levels in μp or H, or a fundamental problem in bound-state QED, an unknown effect related to the
proton or the muon, or an experimental error.
We present a review on the research carried out with the Micro-Hole & Strip plate (MHSP) gaseous electron multiplier. In this new device charge multiplication occurs in two stages: radiation-induced electrons are multiplied in small holes and the resulting avalanche is further multiplied on anode strips patterned on the multiplier's bottom electrode. This structure provides fast multiplication process, has a high total gain even in noble gas mixtures and provides good localization properties. Detectors based on this principle have shown gains above 10<sup>4</sup> and energy resolution of about 14% for 5.9-keV X-rays; large gains were obtained at high gas pressures as well, allowing for efficient detection of higher-energy X-rays. The properties of UV-photon detectors comprising an MHSP coupled to semitransparent CsI photocathodes or with reflective ones deposited on the multiplier's top surface were investigated. The operation mechanism of these detectors and their most significant results are presented.