REPOSITIONING ACCURACY - COMPARISON OF A NONINVASIVE HEAD HOLDER WITHTHERMOPLASTIC MASK FOR FRACTIONATED RADIOTHERAPY AND A CASE-REPORT

Purpose: To compare accuracy, clinical feasibility, and subjective pat ient impression between a noninvasive head holder (Vogele Bale Hohner [VBH]; Wellhoefer Dosimetry, Schwarzenbruck, Germany) developed at the University of Innsbruck and the thermoplastic mask fixation system fo r use in fractionated external radiotherapy. We present a case report of an actual patient fixated in the VBH head holder during radiation t herapy. Materials and Methods: The VBH head holder consists of an indi vidualized vacuum dental cast connected to a head plate via two hydrau lic arms allowing noninvasive, reproducible head fixation of even unco operative patients. Accuracy was tested and compared with that of the thermoplastic mask using the Phillips EasyGuide navigation system on f ive volunteers. Specific external registration points served as landma rks and their positions were compared after each repositioning. System and operator inaccuracy were also taken into account. The times taken for production and repositioning of the respective fixation devices m ere compared, and subjective impressions were noted. Results: Mean VBH head holder repositioning accuracy was 1.02 mm while that of the ther moplastic mask was 3.05 mm. 69% of mask repositionings showed a deviat ion >2 mm and 41% >3 mm (as opposed to 8% and 1% respectively for the VBH head holder) Those points located farthest away from the respectiv e plane of fixation showed the largest deviations. Both production and repositioning times were similar between the systems; depending upon the patient, the VBH head holder was generally better tolerated than t he mask system. Conclusion: Due to its significantly better reposition ing accuracy compared to that of the thermoplastic mask, the VBH head holder is especially suited for external radiation requiring precise r epositioning due to critical tissues in immediate surrounding of the a rea to be irradiated. (C) 1998 Elsevier Science Inc.