Dynamic radiotherapy: interactive movement of patient couch for treatment of craniospinal axis

The various techniques that have been described for treatment of the craniospinal axis show the common challenge of edge matching between adjacent orthogonal and parallel photon beams. Such edge matching is needed because the maximum field length provided by modern treatment machines is generally insufficient to treat adults with less than three matching fields. Using the common techniques, field edge matching becomes difficult, if for medical reasons, the patient cannot be treated in the prone position.

A scanning couch technique is proposed, with the patient lying in supine position. After treating the cerebral and upper neck regions by two lateral opposed half beam fields defined by asymmetric collimators (split beam), the patient is being moved along the spinal axis through an 8.0 cm wide by 15.0 cm long posterior split beam (allowing edge matching with the lateral fields at the neck region) by means of remote controlled couch movement. Stopping and starting of the scanning field resulted in a linear decrease of dose on both sides of the scan. Two ways of resolving this problem were investigated.

The administered dose varied less than 8.5% through the craniospinal axis. Flatness of the rectangular scanned field was 0.76%. Apart from dose homogeneity, patient comfort and decreased simulation time are major advantages.

The proposed technique represents a suitable alternative using a common linear accelerator, requiring a remote couch controller as an additional component.