Influência dos métodos na determinação dos campos equivalentes para o cálculo das doses no tratamento com Teleterapia

Abstract

Radiotherapy is one of the most used treatments to treat tumor cells, using so-called ionizing radiations. Radiotherapy treatment can be divided into two modalities, Brachytherapy and Teletherapy. The Brachytherapy can be considered an inside-out treatment that is, the radioactive source in direct contact with the lesion and the Teletherapy an outside-in because the radioactive source is some distance from the patient. The latter being the high energy X-Ray type treatment that are generated by na equipment, such a Linear Accelerator. For its use, it must be made its commissioning, that is, the determination of all the parameters that will be used for the precise definition of the doses (monitor units) in the teletherapy treatments, being normally made for square fields. As most of the fields used in the treatments have shapeless formats to protect structures that shouldn’t be irradiated, an important parameter for defining the treatment doses are the so-called “equivalent fields in radiotherapy”. To obtain these equivalent fields and later the monitor units, three methods were used: the first is the method that uses an empirical equation, the second uses the Scattering Function and the third is determined using the Varian Eclipse Planning System. In this work we made a comparison of the influence of the equivalent fields determined by these three methodologies, in the definition of the monitoring units used in the treatment of a colorectal cancer.