Navigation system for interstitial brachytherapy.
OBJECTIVE
To develop a computed tomography (CT) based electromagnetic navigation system for interstitial brachytherapy. This is especially designed for situations when needles have to be positioned adjacent to or within critical anatomical structures. In such instances interactive 3D visualisation of the needle positions is essential.


METHODS
The material consisted of a Polhemus electromagnetic 3D digitizer, a Pentium 200 MHz laptop and a voice recognition for continuous speech. In addition, we developed an external reference system constructed of Perspex which could be positioned above the tumour region and attached to the patient using a non-invasive fixation method. A specially designed 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 metallic needles within the phantoms was in the range 2.0-4.1 mm with a maximum of 5.4 mm. This is an improvement on the accuracy of a CT-guided technique which was in the range 6.1-11.3 mm with a maximum of 19.4 mm. The mean reconstruction accuracy of the implant geometry was 3.2 mm within a non-ferromagnetic environment. We found that although the needles were metallic this did not have a significant influence. We also found for our experimental setups 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 structures have to be avoided. It also should provide a significant improvement on our existing technique.
Strassmann
G
G
Städtische Kliniken Offenbach, Strahlenklinik, Offenbach, Germany.
Kolotas
C
C
Heyd
R
R
Walter
S
S
Baltas
D
D
Martin
T
T
Vogt
H
H
Ioannidis
G
G
Sakas
G
G
Zamboglou
N
N
D001918:Brachytherapy; D055590:Electromagnetic Phenomena; D006801:Humans; D019047:Phantoms, Imaging; D011881:Radiotherapy, Computer-Assisted; D014057:Tomography, X-Ray Computed