Modification of Gill-Thomas-Cosman frame for extracranial head-and-neck stereotactic radiotherapy

Purpose: A modification of a commercially available, noninvasive, relocatable, stereotactic Gill-Thomas-Cosman (GTC) head frame is presented for treatment of extracranial lesions of the head and neck, base of the skull, and inferior nasopharyngeal region. Methods and Materials: Skull-based and nasopharyngeal lesions cannot be treated with the GTC frame because it obstructs the beam path. To treat those lesions, the GTC frame was modified without compromising the integrity, flexibility, or use of the treatment software. The modification uses a set of aluminum extension rods of variable lengths and bevels to support a modified dental plate. The extension rods allow the dental tray and attached GTC frame to be lowered so that the more inferior regions may be treated. Ten patients underwent CT with the modified frame and CT localizer. For some patients, MRI was acquired without the frame. Image fusion of MRI and CT scans was used to delineate the target volume, and planning was done with the existing software for proper treatment. Results: The modification of the GTC frame has been successful in imaging, planning, and extending the treatment domain for the base of the skull, nasopharyngeal regions, and other superior lesions of the head and neck. The reproducibility of the modified frame and the patient localization helmet technique was identical to that of the unmodified frame. Conclusion: The modification of the GTC frame is simple and accurate. It provides flexibility in treating an extended range of the base of the skull, nasopharyngeal region, and other superior lesions of the head and neck that otherwise could not be treated with the GTC frame.