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TU-H-CAMPUS-TeP1-02: Seated Treatment: Setup Uncertainty Comparable to Supine.

PURPOSE
For some head and neck patients, positioning in the supine position is not well tolerated. For these patients, treatment in a seated position would be preferred. We have evaluated inter- and intra- fraction uncertainty of patient set-up in a novel treatment chair which is compatible with modern linac designs.


METHODS
Five head-and-neck cancer patients were positioned in the chair, fitted with immobilization devices, and imaged with orthogonal X-rays. The couch (with chair attached) was rotated to simulate delivery (without actual treatment), another set of images were acquired, providing a measure of intra-fraction displacement. The patient then got off of and back onto the chair and the process was repeated, thus providing a measure of inter-fraction set-up uncertainty. Six sub-regions in the head-and-neck were rigidly registered to evaluate local intra- and interfraction displacement. Image guidance was simulated by first registering one sub-region; the residual displacement of other sub-regions was then measured. Additionally, a patient questionnaire was administered to evaluate tolerance of the seated position.


RESULTS
The chair design is such that all advantages of couch motions may be utilized. Average inter- and intrafraction displacements of all sub-regions in the seated position were less than 2 and 3 mm, respectively. When image guidance was simulated, interfraction displacements were reduced by an average of 4 mm, providing comparable setup to the supine position. The enrolled patients, who had no indication for a seated treatment position, reported no preference for the seated or the supine position.


CONCLUSION
The novel chair design provides acceptable inter- and intra-fraction displacement, with reproducibility similar to that observed for patients in the supine position. Such a chair will be utilized for patients who cannot tolerate the supine position and use with CBCT images for planning, in a fixed-beam linac system, and for other treatment sites is under investigation.


FUNDING
Varian Medical Systems.