Mestrado em Radiações Aplicadas às Tecnologias da Saúde.Precision is an imperative in modern radiotherapy. This concept is applied in a day-to-day basis at all levels in planning and delivering treatment to patients, since only by uniting all these aspects is it’s real application possible. Given that I am a radiation technologist in an institution where the purpose is to ensure accuracy in administered treatment, my main focus was to direct this work towards the field in which I dwell daily. Indeed, making sure that all instruments available have a precisely studied role in the quality of the execution of prescribed treatment has become a necessity that justifies the enormous amount of care put in the treatment phase in radiotherapy. This applies, namely, to the recently-implemented cone-beam computed tomography (CBCT) tool. Therefore, computerized tomography dose indices (CTDI) were acquired in order to monitor doses administered to patients through CBCT. This was followed by the selection of twenty one patients of pathologies involving a great amount of precision: fourteen patients with prostate and seven patients with head and neck tumours. This sample was characterized with the acquisition of CBCT pre and post-treatment, as well as after any correction performed on their positioning. This allowed for evaluating intra-fraction errors. From within this sample, patients out of action limits were chosen, as analyzed in control charts for mean and standard deviation of their positioning deviations, as well as patients out of tolerance limits for deviation correction.
Finally, new dosimetric distributions were performed, in which the isocenter accounts for the measured positioning errors. The doses in organs at risk and eventual differences in planning target volume (PTV) coverage with 95% of the dose between these and the planned distributions were compared for each of these patients. This simulation allowed for inferring what would have happened had these errors not been accounted for and corrected. This study also evaluated the feasibility of using CBCT in the imaging verification during the treatment of patients with the aforementioned pathologies, as well as the adequacy of the image acquisition protocol, as currently implemented at the department. The evaluation and quantification of systematic and random translational and rotational errors was also made possible, as defined by current departmental practices. This allowed for adapting not only the mentioned protocol, but also margins currently added to clinical target volumes (CTV) for PTV generation. This will allow to ensure that protocols are based on data obtained locally, which will undoubtedly procure better results in cancer healthcare at the department. It is noteworthy that the Master Comission authorized the presentation of this work as a scientific article, with the purpose of future publication in international, peer-reviewed journals. In order to do so, it is not only written in English, but it also respects criteria related to this objective. In the first part, a review on state-of-the-art literature is rendered (previously submitted in May 2011, even though some aspects have been corrected or updated), as to allow for a contextualization of my work. The feasibility of the IGRT protocol, as implemented at my department, is then assessed. Finally, as previously discussed, systematic and random translational and rotational errors are evaluated
