Proc. SPIE. 10058, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVII
KEYWORDS: Signal to noise ratio, Optical fibers, Polymethylmethacrylate, Breast cancer, Tumors, Fiber optics, Scintillators, Radiotherapy, Radiation dosimetry, High dynamic range imaging, Computed tomography, Gamma radiation, Prostate cancer, Silicon photomultipliers, In vivo imaging, Iridium
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.