MAGNETIC-RESONANCE GUIDED RADIOSURGERY IN CHILDREN - TRIDIMENSIONAL EXTRAPOLATION FROM ISODOSE NEUROIMAGING SUPERIMPOSITION

In stereotactic radiosurgery, thin external beams of ionizing radiatio n concentrated in a single dose onto a sharply defined target are empl oyed to treat lesions within the brain, avoiding doses which may produ ce unwanted damage to the surrounding healthy tissue. The dynamic irra diation technique used with the linear accelerator employs variable ar cs of irradiation rotating around the isocenter of the target. The tec hnique of stereotactic magnetic resonance (MR) guided radiosurgery is supported by a dedicated computerized system for treatment planning si mulation. The system, based on a personal computer, allows the acquisi tion, reconstruction, and visualization of the target volume from MR i mages, and permits calculation and visualization of a three-dimensiona l dose distribution directly superimposed upon MR images of the lesion . The desired goal of destroying neoplastic tissue without damaging ce rebral parenchyma is of particular importance in children. Consequentl y, adapting the three-dimensional isodose profiles to the morphology o f the lesion to be treated is crucial. From this, the importance of th e computer simulation is evident, as it permits one to go deeply into the study of isodose distribution, changing beam collimation, and the number and amplitude of arcs of irradiation.