Chair

A maximum freedom in the choice of the irradiation angle is desireable to get an optimum dose conformation onto the target volume while best sparing healthy tissue and especially organs at risk. The equipment of Cave M, a horizontal beam in combination with a treatment couch on which the patient is fixed lying on his back,  offers only a limited angular range. As the realisation of a turnable beam line (gantry) for getting larger angular ranges would have been too expensive, a chair has been developed for the irradiation of patients in upright sitting position. The main characteristics of this chair are that it is isocentric (its two rotational axis cross in that point in the room which is fixed by the laser system and corresponds to the point of origin of the beam) and that it can be moved from a parking position into the irradiation position in a short time. The chair has been conceived for tumors in the head and neck region exclusively. It has five degrees of freedom: three translations for the adjustment of the target point, one rotation around the longitudinal axis of the patient and one rotation around a horizontal axis fixed in the room.

Principal parts of the mechanics have been designed, built and optimized at GSI, e.g. the fixation unit which fixes the patient in a secure, stable and comfortable way. The techniques of mask fixation and stereotactical positioning are the same as with the patient couch and have been adopted from DKFZ.