Ruprecht-Karls-Universität Heidelberg
Optimization in Robotics and Biomechanics

3D Planning of optimal needle trajectories for robot assisted prostate brachytherapy

Marina Horn, Katja Mombaur, IWR
Armin Schäfer, Auguste van Poelgeest, Jan Stallkamp, Fraunhofer PAMB Mannheim
Daniel Bürgy, Frederik Wenz, Medizinische Fakultät Mannheim, Universität Heidelberg

Brachytherapy (Radioactive Seed Implantation Therapy) is a minimal invasive treatment for prostate cancer. In this method, radioactive seeds are implanted into a patient's prostate by using rigid needles with an asymmetric tip. Depending on the size and location of the tumor within the prostate, the required rate of dose and the positions of the seeds are determined. This calculation is performed by a sophisticated computer program. In the current robot-assisted brachytherapy, template grids are used to guide the needles. The deficiency of this method is the limitation to horizontal and straight movements of the needles (Figure 1). Hence there could be inaccessible seed positions predetermined, in the case the pelvis location of some patients is disadvantageous to reach some parts of the prostate.

 

In collaboration with the Fraunhofer project group PAMB (Automation in Medicine and Biotechnology) in Mannheim and the Medical Faculty Mannheim at the Heidelberg University, we are working on a method to replace the template grids by a medical robotic arm. The goal hereby is to have the possibility of performing needle trajectories with more freedom of movement in 3D space:

 

 

Putting the seeds at the exact defined positions is a big challenge, because the needle insertion induces deformation of the soft tissue which causes a displacement of the seed positions:

 

 

This deformation of the prostate can not be seen on the monitor and therefore it is not possible for the physicians to counteract this effect. Depending on different factors like the insertion angle, the needle can also bend during the injection. These two significant effects have to be taken into account for planning the optimal trajectories. The optimal solution is not simply the shortest path, because it is important to reach the given positions of the seeds with minimal tissue damage and a maximal accuracy. At a brachytherapy treatment, the required number of seeds for an optimal result ranges from 70 to 150, while one needle can place maximum 8 seeds with one insertion. Every new needle insertion stresses the soft tissue, therefore one needle trajectory should reach as many seed positions as possible. This scenario could be seen as the pick-up sticks game mikado with the difference that the sticks are not dropped. Here the needles have to be placed without touching or moving the others and they must reach as many predetermined seed positions as possible:

 

 

 

 

 

 

 

 

K. Mombaur, orb@uni-hd.de
Last Update: 15.05.2013 - 13:19

The photographs in the header of this webpage have been taken at the Musee de l'Automate in Souillac, France