Magnetic resonance guided radiosurgery in children: tridimensional extrapolation from isodose neuroimaging superimposition.

In stereotactic radiosurgery, thin external beams of ionizing radiation concentrated in a single dose onto a sharply defined target are employed to treat lesions within the brain, avoiding doses which may produce unwanted damage to the surrounding healthy tissue. The dynamic irradiation technique used with the linear accelerator employs variable arcs of irradiation rotating around the isocenter of the target. The technique of stereotactic magnetic resonance (MR) guided radiosurgery is supported by a dedicated computerized system for treatment planning simulation. The system, based on a personal computer, allows the acquisition, reconstruction, and visualization of the target volume from MR images, and permits calculation and visualization of a three-dimensional dose distribution directly superimposed upon MR images of the lesion. The desired goal of destroying neoplastic tissue without damaging cerebral parenchyma is of particular importance in children. Consequently, adapting the three-dimensional isodose profiles to the morphology of the lesion to be treated is crucial. From this, the importance of the 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.