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Intensity Modulated Radiation Therapy (IMRT)

Intensity Modulated Radiation Therapy (IMRT) is the standard treatment technique in first-world countries and represents one of the major advancements in the field since the introduction of linear accelerators. Its primary advantage is the ability to achieve concave dose distributions that allow the exclusion of structures to be protected. As its name suggests, Intensity Modulated Radiation Therapy enables the creation of intensity distributions that can be configured to conform to tumor volumes. Such characteristics are impossible to achieve with conventional techniques.

IMRT is based on the use of multileaf collimators. Initially, multileaf collimators were used to improve tumor conformation and protect organs at risk, with the idea of replacing the creation of traditional conformal blocks. However, the independent movement of each leaf during irradiation results in each small leaf modifying the intensity of the radiation beam, leading to different intensity patterns in the same plane for each leaf. An analysis of the dose-volume histograms obtained with IMRT reveals better coverage of the prescribed dose to the tumor with effective protection of organs at risk.

Our multileaf collimator is integrated into the accelerator and consists of 80 leaves (40 on each side, each 1 cm thick). To deliver IMRT treatment, it is vital that each of these leaves is positioned and has the assigned speed at the time of treatment planning. For this purpose, our Medical Physics team is responsible for calculating and treating the same treatment plan designed for a specific patient on a phantom equipped with an array of detectors. The result of the calculated dose distribution on the phantom is compared to the measured dose distribution with the detector array, which is irradiated on the linear accelerator under the same parameters and conditions as the patient. If the results of this evaluation meet the established criteria, then the final treatment plan for the patient is approved. This procedure is what truly ensures that what is displayed in the planning computer is what will be administered to the patient.