Navigation system for interstitial brachytherapy

Purpose: To develop a computed tomography (CT) based electromagnetic naviga tion system for interstitial brachytherapy. This is especially designed for situations when needles have to be positioned adjacent to or within critic al anatomical structures. In such instances interactive 3D visualisation of the needle positions is essential. Methods and materials: The material consisted of a Polhemus electromagnetic 3D digitizer, a Pentium 200 MHz laptop and a Voice recognition for continu ous speech. In addition, we developed an external reference system construc ted of Perspex which could be positioned above the tumour region and attach ed to the patient using a non-invasive fixation method. A specially designe d needle holder and patient bed were also developed. Measurements were made on a series of phantoms in order to study the efficacy and accuracy of the navigation system. Results: The mean navigation accuracy of positioning the 20.0 cm length met allic needles within the phantoms was in the range 2.0-4.1 mm with a maximu m of 5.4 mm. This is an improvement on the accuracy of a CT-guided techniqu e which was in the range 6.1-11.3 mm with a maximum of 19.4 mm. The mean re construction accuracy of the implant geometry was 3.2 mm within a non-ferro magnetic environment. We found that although the needles were metallic this did not have a significant influence. We also found for our experimental s etups that the CT table and operation table non-ferromagnetic parts had no significant influence on the navigation accuracy. Conclusions: This navigation system will be a very useful clinical tool for interstitial brachytherapy applications, particularly when critical struct ures have to be avoided. It also should provide a significant improvement o n our existing technique. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.