Daily patient set-up control in radiation therapy by coded light projection.

Advances in conformal radiation therapy to control disease via dose escalation are challenged by set-up uncertainties. Recently, techniques have been developed to use surface features to evaluate the patient's position and correct it where necessary. The aim of this study was to use the patient's surface as a tool for daily set-up control and monitoring. We use a surface scanner based on the projection of coded light to receive--in a daily routine--a large amount of surface points which enables us to register the CT-based planning data with the patients current position. By superimposing current and planned volumes, a volume of congruency was obtained. An error below 1 mm was considered acceptable. In cases where set-up was not satisfactory a map of the surface comparison was evaluated showing the areas of missing alignment. According to this information a manual repositioning was performed. This procedure was repeated until the error was acceptable. No more then 3 repetitions where necessary to obtain an acceptable result. The whole procedure including registration, calculation and visualization took about 20 sec for one repetition. The use of structured light projection in the daily set-up control and monitoring proved to be a noninvasive, easy, quick, inexpensive and reliable solution.

Integration of intraoperative radiotherapy (IORT) dose distribution into the postoperative CT-based external beam radiotherapy (EBRT) treatment planing.

In the treatment of malignant disease external beam radiation therapy (EBRT) is often combined with surgery. Intraoperative radiotherapy (IORT) improves the local control by dose escalation. For reasons of recording, improvement and security of the intervention, it would be necessary to merge the IORT-dose distribution with the postoperative CT-based EBRT-planing. The aim of this work was to develop a method to reconstruct the IORT field and register it with the postoperative planing CT. This enables the reconstruction of the IORT dose distribution and merge it with the CT-based EBRT planing data. We use a surface scanner to receive a large amount of surface points which enables us reconstruct the IORT-field and to register it with the CT-based EBRT planning data. Scanning and calculation time is not over 2 seconds, depending mainly on the CPU power. The error of a single point is below 1 mm. The density of the point cloud is approx. 4 per mm2. In this paper we give an overview of our experimental setup and the accuracy of the method.

Safety in computer assisted surgery.

Today, surgeons accept computer assisted technologies as important tools to enhance the treatment of a patient. The positive impact and acceptance of computer assisted technologies could be increased to a great extent, if all methods and devices used for diagnosis and treatment of a patient are better co-ordinated and more finely tuned. Often computer assisted treatments cannot be performed due to a lack of communication between hospital departments, useless patient data, deficient interfaces, etc. Risks for the patient and potential errors within the treatment are often unrecognised, as up to now the safety of computer integrated surgery is only product-, device and security oriented. We have developed a new approach for a safety architecture, which includes safety aspects considering patients, users, interdependencies and interactions of computer assisted methods and apparatuses.

Computer aided planning device for preoperative bending of osteosynthesis plates.

In craniofacial surgery bone fractures and repositioned bone segments often have to be fixed by titanium miniplates. In clinical routines the surgeon has to fit each miniplate t be used to the individual bone structure of the patient: bending and fitting of a miniplate must frequently be repeated several times. Often up to twenty minutes are required to achieve the best fit of a single osteosynthesis plate. As a patient usually receive several miniplates for bone fixture, he will be exposed to long anaesthesia. In co-operation with the surgeons of the Clinic of Maxillofacial surgery at the University of Heidelberg we have conceived a planning system for the preoperative positioning of miniplates on a model of the patient's skull. The appropriate bending is computed and the bending data are stored for later use by a bending device and an intraoperative positioning aid. The principles of our computer-aided tool are presented in this paper.