PATIENT POSITIONING FOR FRACTIONATED PRECISION RADIATION TREATMENT OFTARGETS IN THE HEAD USING FIDUCIAL MARKERS

When irradiating targets in the brain, an accurately localised dose is often needed. One crucial moment to achieve this is the positioning o f the patient. We have developed a positioning method where the patien t is immobilised with a bite block and a head mould, and where the pos ition of the target is determined by X-ray imaging of fiducial markers that are placed in the patient's skull. A method for computing the tr ansformation needed to move the target from the observed to the prescr ibed position and orientation is described. This method uses the infor mation from two orthogonal X-ray images and takes measurement errors a nd data from three or more markers into account. Results from using th e method clinically in proton beam therapy are given.