Estudo dosimétrico da braquiterapia de Ho-166 em próstata e desenvolvimento experimental correlato

Abstract

There is now a need to improve therapeutic techniques and suggest new possibilities for the treatment of prostate tumors, considering the high incidence of the disease and the significant morbidity rates associated with surgery and radiotherapy. Simulations in brachytherapy produce essential information on dosimetric efficiency and effectiveness, and can compare different radiotherapy techniques. This work studies the experimental and computational dosimetry in brachytherapy using ceramic seeds of Ho-166. The development of this project was divided into experimental and computational dosimetry. To obtain the experimental dosimetry, the physical phantom, denominated Anatomic Object Simulator (OAS) was elaborated. This reproduced anatomically-equivalent part of the male pelvis: the prostate, and the tissue material (MTE) for, which proposes to reproduce the composition of the tissues of the human body and its radiological and echographic response. OAS presented the anthropomorphic and anthropometric characteristics necessary for dosimetric experimentation. A stepper device called the Prostate Seed Implant System (SISP) was also developed. The SISP operates the ultrasound probe and the set of needles used in the implant. The mechanical design of the SISP involved a set of independent pieces that fit together. The prototype of the SISP obtained the essential characteristics desired: support capacity for the ultrasound probe with a longitudinal movement. For the computational dosimetry, we performed simulations of volumetric distributions of absorbed doses using two spatial distributions of Ho-166 seeds, in a prostate model. Changes in seed distributions were studied by varying horizontal spacing between fillets. The spatial dose distributions and dose versus volume histograms were obtained for each of the seed distributions studied. It was possible to evaluate an adequate distribution for implants of Ho-166 seeds in the prostate, which was shown to be a function of the injected seed activity. A comparative computerized dosimetric study was also carried out considering the dosimetry produced in two implant conditions: with Ho-166 and I-125 seeds, both elaborated by the NRI research group for the purpose of prostatic brachytherapy. An initial seed larger activity was obtained for seeds of Ho-166 to guarantee the same prescribed dose in both implants. The doses at the risk organs (rectum and bladder) with Ho-166 were well below the values found for the distribution of I-125 seeds.