DYNAMIC RADIOTHERAPY - INTERACTIVE MOVEMENT OF PATIENT COUCH FOR TREATMENT OF CRANIOSPINAL AXIS

Purpose: The various techniques that have been described for treatment of the craniospinal axis show the common challenge of edge matching b etween adjacent orthogonal and parallel photon beams. Such edge matchi ng is needed because the maximum field length provided by modern treat ment machines is generally insufficient to treat adults with less than three matching fields. Using the common techniques, field edge matchi ng becomes difficult, if for medical reasons, the patient cannot be tr eated in the prone position. Methods and Materials: A scanning couch t echnique is proposed, with the patient lying in supine position. After treating the cerebral and upper neck regions by two lateral opposed h alf beam fields defined by asymmetric collimators (split beam), the pa tient is being moved along the spinal axis through an 8.0 cm wide by 1 5.0 cm long posterior split beam (allowing edge matching with the late ral fields at the neck region) by means of remote controlled couch mov ement. Stopping and starting of the scanning field resulted in a linea r decrease of dose on both sides of the scan. Two ways of resolving th is problem were investigated. Results: The administered dose varied le ss than 8.5% through the craniospinal axis. Flatness of the rectangula r scanned field was 0.76%. Apart from dose homogeneity, patient comfor t and decreased simulation time are major advantages. Conclusions: The proposed technique represents a suitable alternative using a common l inear accelerator, requiring a remote couch controller as an additiona l component.