Abstract # 2216 Analysis of Interfractional Set-up Errors and Intrafractional Organ Motions during IMRT for Head and Neck Cancers toDefine an Appropriate PTV-margin

Presenter: Suzuki, Minoru

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Consecutive ten patients with head and neck cancers were enrolled for evaluation of interfractional set-up errors. All the patients were immobilized with a thermoplastic mask covering the head, neck and shoulders (Type-S thermoplastic based system, MED-TEC, Orange City, IA). For analyses of the interfractional set-up errors, two orthogonal anterior-posterior (AP) and lateral films were taken both on X-ray simulator at simulation and on the treatment couch at 10 IMRT treatments during 7 weeks. To estimate the interfractional set-up errors, the coordinates of the visible bony landmarks (maxilla, mandible, cervical vertebrae and skull base) on the treatment beam films were compared with the corresponding coordinates on the simulation films. For analyses of intrafractional organ motion errors, twelve patients were enrolled. On the couch of the X-ray simulator which was the same as the treatment couch, the patients were positioned and immobilized with the thermoplastic mask used at treatment. Under the same condition in the IMRT treatment, two orthogonal digital images were taken at 3 minutes interval for 15 min (six times). The bony landmarks analyzed for intrafractional organ motion errors were the same as those for interfractional set-up errors. Displacements of the coordinates of the bony landmarks on the serial images relative to the corresponding coordinates on the initial image were measured as the intrafractional organ motion errors.

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