CT-based navigation systems for intraoperative radiotherapy using the afterloading-flab technique.

Introduction: The fact that conventional intraoperative radiotherapy does not give the opportunity to exactly document the radiation volume applied and the dose distribution has been criticized in many ways. We would like to introduce a system for surgical navigation and documentation of flap positioning in intraoperative brachytherapy using the afterloading flap technique.

Methods: Our system consists of an electromagnetic 3D-digitizer and a PC workstation. Spiral CT scans of the tumor region taken preoperatively are used for navigation and documentation of flap positioning, analogous to the procedure in neuronavigation. Registration is done via an external reference system which is attached to the iliac bone of the patient.

Results: The mean accuracy of digitalization of the 100 spheres in a pelvis model is about 2.6 +/- 0.5 to 3.7 +/- 9.9 mm. The mean navigation accuracy is 2.4 +/- 0.8 to 3.3 +/- 0.8 mm. These figures correspond to the clinical experience of our surgeons.

Discussion: The optimization of flab positioning by CT-guided navigation and the more accurate documentation of the dose volume and distribution in the patient is an important step on the way to improving the quality of individual radiation therapy. We are of the opinion that surgical navigation in the pelvic region should be subject to additional investigation in order to optimize the procedure.