Fifty-sixth annual meeting of the American association of physicists in medicine
SU-C-19A-05: Treatment Chairs for Modern Radiation Therapy Treatments
Treating patients in a seated position has potential advantages including improved comfort, increased lung volume, and reduced respiratory motion. We compared chair designs for head and neck, thoracic and breast patients for use with either IGRT linacs or a proposed low-cost fixed horizontal beam-line machine.
Three treatment chairs were designed and constructed. Two of the chairs are based on a massage-chair, with the patient angled slightly forwards and knee rests used to minimize intra-fraction slouch. The third chair design is more conventional; the patient is angled backwards, with indexed positioning devices and the ability to attach thermoplastic masks. Patient geometries, including PTV location and patient sizes, were extracted from 137 CTs of past patients were used to model the probability of collision between the patient and the linac for various seated positions. All chairs were designed around the weight limits for couches on our linacs. At the time of writing we have just received IRB approval for imaging studies to evaluate comfort, and intra- and interfraction reproducibility.
The geometric analysis showed that head and neck patients and thoracic patients could be treated without collision. However, there is very limited space between the patient and the treatment/imaging devices, so careful design of the chair is essential. The position of the treatment target and extended arm positioning means that this is a particular concern for thoracic and breast patients. This was demonstrated for one of the prototype chairs designed for breast treatment where the arm holders would collide with the kV detector. The extra clearance of a dedicated fixed-beam linac would overcome these difficulties. Intra- and inter-fraction reproducibility results will be presented at the meeting.
To take advantage of the clinical advantages of seated treatments, appropriate treatment chairs are needed. A dedicate fixed-beam linac may enable more options.
This work was partially funded by Varian Medical Systems