Risk analysis and safety assessment in surgical robotics: a case study on a biopsy robot.

One of the most important issues in medical robotics is safety and integration into the clinical workflow. If a robot is not safe and its use is complicated by difficult handling and complex user interfaces physicians would not use a robotic system during clinical patient trials, whatever the other advantages are. However, there are only few publications on this topic, in particular on risk management in developing a robotic prototype (for clinical trials). In this paper risk management and the safety of using robot-assisted surgery equipment are discussed and demonstrated exemplarily in the process of developing a prototype biopsy robot.

A medical workstation for the evaluation of alternative 3D radiotherapy treatment plans.

A medical workstation for the evaluation of alternative 3D radiotherapy plans is described. Our system can simultaneously apply qualitative as well as quantitative evaluation methods to as many as three 3D dose distributions. The user interface of the workstation has been designed with the demands of radiation oncologists in mind. The handling of the large amounts of 3D data (CT data, up to three 3D dose distributions, volumes of interest) is assisted by computer graphics.

Optimization and evaluation of landmark-based image correlation.

Image correlation methods enable the complementary use of information from different medical images of a patient. These images can be obtained from different imaging devices (CT, MR, PET), or, from one imaging device taken at different times. Unfortunately, there are few cases in which the requirements for later image correlation are taken into account at the time of image acquisition. There is therefore a need for correlation techniques requiring no preparation in advance. We have developed two correlation methods, both based on three or more anatomical or artificial landmarks, to be defined in corresponding image data sets. These methods have been evaluated with phantom data as well as with patient data. We have improved these correlation methods by using more landmarks and special selection criteria. They are applicable to all medical tomograms and to x-ray pictures taken under stereotactical conditions. The results obtained have error ranges in the order of the three-dimensional image resolution.

Modification of a three-dimensional treatment planning system for the use of multi-leaf collimators in conformation radiotherapy.

The multi-leaf collimator of the DKFZ is designed as a low cost add-on device for conventional linear accelerators for radiotherapy. The technical specification of the computer controlled collimator is described briefly. A major limitation in the use of the wide capabilities of multi-leaf collimators in the clinic is still an appropriate treatment planning system. This paper describes treatment planning and dose calculation techniques for multi-leaf collimators and shows examples where the capabilities of the collimator are used extensively.

Three-dimensional photon radiotherapy planning for laryngeal and hypopharyngeal cancers. 1. Conventional rotational technique.

Three-dimensional dose distributions have been computed for the photon radiation therapy of laryngeal and hypopharyngeal cancers, using biaxial and eccentric rotatory techniques. Treatment plans obtained under various conditions of irradiation with a 15 MV linear accelarator (MEVATRON 77, Siemens) are analysed and compared. Dose delivery to the tumour and the degree of spinal cord protection are evaluated for both treatment techniques. The eccentric plan is somewhat superior to the biaxial one, suggesting a justifiable preference to use this method in the radiation treatment of these tumours. Simulations show that extreme care is needed in positioning the axis: an accuracy of +/- 3 mm is required in the sagittal plane.

Three-dimensional treatment planning for conformation therapy of a bronchial carcinoma.

Three-dimensional (3-D) radiotherapy planning is applied for the conformation therapy of a bronchial carcinoma. The treatment technique, using dynamically controlled shielding blocks, and the treatment planning procedure are described. The method has now been in clinical routine since 4 years; problems with the patient's positioning are discussed.

Three-dimensional photon radiotherapy planning for laryngeal and hypopharyngeal cancers. 2. Conformation treatment planning using a multileaf collimator.

Three-dimension dose distributions have been computed for 15 MV X-ray radiation therapy (MEVATRON 77, Siemens) of laryngeal and hypopharyngeal cancers using isocentric rotational technique with multileaf collimator. Using a new concave contour tracing algorithm, satisfactory dose delivery to the target volume and efficient protection of the normal tissues can be achieved.

Methods of image reconstruction from projections applied to conformation radiotherapy.

The problem of optimizing the dose distribution for conformation radiotherapy with intensity modulated external beams is similar to the problem of reconstructing a 3D image from its 2D projections. In this paper we analyse the relationship between these problems. We show that the main image reconstruction methods, namely filtered backprojection and iterative reconstruction, can be directly applied to conformation therapy. We examine the features of each of these methods with regard to this new application and we present first theoretical results.

Treatment planning for conformation therapy using a multi-leaf collimator.

In high energy photon therapy an optimum dose distribution is achieved with an irradiation from several directions, thus adapting the field shape to the target volume. Some methods of irradiation planning using these techniques are presented. The result of such a treatment planning is demonstrated.

Three dimensional image correlation of CT, MR, and PET studies in radiotherapy treatment planning of brain tumors.

A treatment planning system for stereotactic convergent beam irradiation of deeply localized brain tumors is reported. The treatment technique consists of several moving field irradiations in noncoplanar planes at a linear accelerator facility. Using collimated narrow beams, a high concentration of dose within small volumes with a dose gradient of 10-15%/mm was obtained. The dose calculation was based on geometrical information of multiplanar CT or magnetic resonance (MR) imaging data. The patient's head was fixed in a stereotactic localization system, which is usable at CT, MR, and positron emission tomography (PET) installations. Special computer programs for correction of the geometrical MR distortions allowed a precise correlation of the different imaging modalities. The therapist can use combinations of CT, MR, and PET data for defining target volume. For instance, the superior soft tissue contrast of MR coupled with the metabolic features of PET may be a useful addition in the radiation treatment planning process. Furthermore, other features such as calculated dose distribution to critical structures can also be transferred from one set of imaging data to another and can be displayed as three-dimensional shaded structures.

Stereotactic percutaneous single dose irradiation of brain metastases with a linear accelerator.

The effectivity of stereotactic percutaneous single dose irradiations in the treatment of solitary brain metastases has been assessed in a series of 12 consecutive patients. Only radioresistant deeply localized metastases have been treated. Photon-irradiation was carried out with the convergent beam technique using stereotactic localization methods, in a linear accelerator facility. In 11 of the 12 patients no side effects occurred. The first 7 patients, who could be observed 3 months or longer, have been studied in detail. In each of these cases single dose irradiation with 20-30 Gy yielded arrest of tumor growth. In one case a marked decrease in contrast enhancement and in four cases shrinkage of the metastasis as well as a marked decrease of the edema occurred. In every patient a marked, sometimes dramatic improvement of the clinical condition was achieved, beginning a few days after irradiation. Stereotactic radiosurgery is a valuable tool in the treatment of inoperable, radioresistant brain metastases, the major advantage being high efficacy and smoothness of the procedure, as well as extremely short hospitalization times (2-3 days).

Display of organs and isodoses as shaded 3-D objects for 3-D therapy planning.

We have developed a technique that allows the user to assess and modify 3-D dose distributions in planning a treatment. Organs and superimposed isodoses can be displayed as shaded solid objects from any desired point of view. The graphic tools necessary are described in detail. Briefly, after the volumes of interest have been defined as contours taken from CT scans, the beam data can then be defined using the "beam's eye view" technique. Subsequently, the desired isodoses can be extracted from the three-dimensional dose matrices and displayed as a series of "barrel hoops" over the target volume. We have found this technique to be particularly useful for development of treatment plans where the spatial relationship of sensitive organs such as the spinal cord may change considerably within the treatment volume. Such a case is described in detail.