Métricas en el control de calidad individualizado de técnicas volumétricas y su aplicación a la patología de próstata

Resumen

I.1. Introduction to volumetric techniques. People treated with radiation therapy techniques are about 6 million over the world. The main aim of radiation therapy is to deliver an accurate amount of radiation to a target volume (tumor), reducing the dose on the surrounding normal tissues. Development of modern medical imaging techniques, as computed tomography (CT) imaging, combined with collimation technologies, such multileaf collimator (MLC) systems, have allowed the introduction of 3D conformal radiation therapy (3DCRT). However, several locations, as head and neck or prostate, demand concave dose distributions in order to spare normal tissues. Intensity-modulated radiation therapy (IMRT) techniques deliver a non-uniform fluence, resulting in dose distributions with a high degree of dose conformity. Traditional IMRT modalities use fixed gantry positions, with multiple static (step-and-shoot) and dynamic (sliding window) beams. Rotational IMRT delivery was firstly proposed in 1995 as intensity-modulated arc therapy (IMAT), combining dynamic MLC and gantry movement. Nevertheless, several overlapped arcs were needed in order to obtain highly conformed dose distributions, such those resulting from traditional IMRT techniques. Improvements in the performance of MLC systems, together with rotational capabilities recently implemented in conventional linacs, have made possible the development of volumetric-modulated arc therapy (VMAT). MLC, gantry speed and angle, and dose rate are continuously modified during the treatment, treating the whole target volume in each gantry rotation (volumetric delivery). This kind of modulated technique leads to improve significantly treatment times compared to traditional IMRT modalities. In addition, the amount of monitor units (MU) in VMAT delivery is reduced, resulting in an improved efficiency compared with traditional IMRT. However, the synchronization of all variable parameters raises the complexity in VMAT treatment delivery from conventional IMRT techniques, leading to increase the efforts in quality assurance (QA) programs...