Accuracy of 3-d needle navigation in interstitial brachytherapy in various body regions.

Background: Precise immobilisation of a patient during extracranial stereotactic 3-D navigation is essential in order to minimize the patient's movement during CT data recording and needle application. In this paper we report the first results of needle positioning accuracy in various body regions, using a 3-D navigation system for brachytherapy and a new patient immobilisation system.
Patients and Methods: Six patients with different manifestations of neoplastic diseases were immobilized by a special vacuum system and treated with stereotactic 3-D navigational interstitial brachytherapy.
Results: The comparison of the simulated stereotactic needle positions with the actual needle positions resulted in a mean positioning deviation varying from 3.4 to 6.5 mm for 29 needles. The maximum positioning deviation lay between 5.7 and 13 mm.
Conclusion: The results of our study show that, despite effective patient immobilisation, an increase in needle positioning accuracy is limited by the method of stereotactic 3-D navigation. Effects such as modification of body shape caused by the needle application morphologic alterations, and inherent inaccuracies within the navigation system have an important influence upon accuracy, which it is not yet possible to calculate.