Avaliação da incerteza no posicionamento em Radiocirurgia com a mesa de tratamento angulada utilizando sistema de IGRT

Abstract

Fractionated whole brain radiotherapy has been the standard treatment for brain metastasis, but provides a limited local control of the tumor and frequently, unsatisfactory clinical results. Stereotactic radiosurgery has overcome several of these limitations, influencing treatment recommendations (Lippitz, B., 2013). In this technique a high dose (≥ 18 Gy) is given in small lesions and in a single session, so it is extremely important to obtain a high accuracy in the positioning. Positioning precision can be achieved by using Image-Guided Radiotherapy (IGRT) as volumetric (CBCT) or planar images (ExacTrac®, MV). In this high-dose delivery in a single application, in order to maximize healthy brain tissue, it is necessary to use non-coplanar fields and thus it is necessary to ensure that the patient's positioning is as close as possible to what was planned, including when moving the couch of treatment.The object of this study is to evaluate the positioning uncertainty in frameless radiosurgery techniques with couch angulation as Alabama s technique as well as validate the reliability of MV images for positioning verification. To perform measurement, the Varian Medical Systems HyperArc® treatment optimization software was used as bases. Images of the techniques Cone Beam CT and MV were taken. The measurements were made with the treatment couch at zero degree and with angulation, inserting phantom s positioning errors in order to verify the efficiency in the identification and correction of the positioning by the robotic couch through image registration between the DRR (Digitally Reconstructed Radiographs) generated by the planning system and the generated image. With the data already collected it was possible to verify the global error generated when the treatment couch is angulated through the statistical treatment. In the global error, uncertainties of types A and B were inserted and through quadratic sum the expanded system uncertainty was calculated with 95% of confidence level. The study made viable to conclude that it is possible to identify the existence of error in the positioning of the patient when the treatment couch is angulated and that this error can be identified with images MV, both with the gantry at zero and at 180 degrees, enabling table angulations for images and treatment as the HyperArc® technique. These images, based in this technique, can optimize the treatment, making it last less, increasing patient comfort and decreasing the probability of movement during the process. It is important to emphasize that this optimize of the treatment occurs safely in order to decrease the risk of collision between the treatment couch with the gantry