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Seated Treatment: Setup Uncertainty Comparable to Supine

R McCarroll

R McCarroll1,2*, B Beadle1 , D Fullen1 , P Balter1 , D Followill1 , F Stingo1 , J Yang1 , L Court1 , (1) UT MD Anderson Cancer Center, Houston, TX, (2) UT Health Science Center, Graduate School of Biomedical Sciences, Houston, TX


TU-H-CAMPUS-TeP1-2 (Tuesday, August 2, 2016) 4:30 PM - 5:00 PM Room: ePoster Theater

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.

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 inter-fraction 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.

The chair design is such that all advantages of couch motions may be utilized. Average inter- and intra-fraction displacements of all sub-regions in the seated position were less than 2 and 3 mm, respectively. When image guidance was simulated, inter-fraction 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.

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 Support, Disclosures, and Conflict of Interest: Funding: Varian Medical Systems

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