A Haptic Interface for Dose Planning in Stereo-tactic Radio-surgery Ida Olofsson ReachIn Technologies, Sweden Karljohan Lundin * Linköping University Sweden Matthew Cooper Linköping University Sweden Per Kjäll Elekta AB Sweden Anders Ynnerman Linköping University Sweden Abstract When planning a Leksell GammaKnife R  treat- ment, dose planners place iso-centres of the irradiation field in such a way that a certain iso-dose surface con- forms as closely as possible to a target, such as a tumour. Today this planning is done primarily in 2D, and the clini- cian places the iso-centres onto the currentmedical image. The images used are usually acquired by MRI, CT or An- giography. In this paper we investigate the use of interactive 3D visualization and haptics to perform the dose planning. In a pilot implementation we provide the user with a virtual en- vironment with real-time graphics to visualize the target, surrounding tissue and iso-dose surfaces as well as an in- tegrated graphical user interface. The overall aim of the im- plementation is to increase the efficiency and precision of the planning process by adding haptic feedback to repres- ent various constraints and opportunities in the planning process and so guide the user to an optimal placement of the iso-centres. Preliminary feedback from potential users has been very positive. Keywords— Surgical Planning, VR environment, haptics, volume haptics, haptic guidance 1. Introduction When treating small targets or targets very close to sens- itive structures in the brain with ionizing radiation the most commonly used procedure is Stereo-tactic Radio-surgery (SRS). A crucial step in the treatment process when using ionizing radiation, is dose planning, during which the clini- cian determines the extent of the region to treat and the dose * karlu@itn.liu.se Figure 1. Tissue visualization through volume rendering with target volume rendered using iso-surfacing. to be delivered to this region. The dose plan is entirely based on the diagnostic information available such as images ac- quired by the use of MRI, CT and/or angiography. When using the Leksell GammaKnife R  for stereo-tactic radio-surgery, the target is irradiated by 201 very narrow beams of Co-60 gamma photons. Because of the high de- gree of symmetry, the dose distribution created during a single irradiation has an almost spherical shape. The dose- planners task is then to “fill” the target volume with irradi- ation iso-centres in such a way that a certain iso-dose sur- face, defining the region within which a sufficient level of ir- radiation is achieved, as closely as possible conforms to the target surface. An example of a target volume can be seen in Fig. 1. It is however not enough only to achieve full tar- get coverage, the dose applied to the tissue outside the target