Automatic selection of non-coplanar beam directions for three-dimensional conformal radiotherapy.

An algorithm is described, based on ray-tracing and the beam's-eye-view, that exhaustively searches all permitted beam directions. The evaluation of the search is based on a general cost function that can be adapted to the clinical objectives by means of parameters and weighting factors. The approach takes into account the constraints of the linear accelerator by discarding beam directions that are not permitted. A sensitivity analysis was carried out to determine appropriate parameters for different sized organs, and a prostate case was used to benchmark the approach. The algorithm was also applied to two clinical cases (brain and sinus) to test the benefits of the approach compared with manual angle selection. The time to perform a beam direction search was approximately 2 min for the coplanar and 12 min for the non-coplanar beam space. The angles obtained for the prostate case compared well with reports in the literature. For the brain case, the mean dose to the right and left optic nerves was reduced by 12% and 50%, respectively, whilst the target dose uniformity was improved. For the sinus case, the mean doses to the right and left parotid glands were reduced by 54% and 46%, respectively, to the right and left optic nerves by 37% and 62%, respectively, and to the optic chiasm by 39%, whilst the target dose uniformity was also improved. For the clinical cases the plans based on optimized beam directions were simpler and resulted in better sparing of critical structures compared with plans based on manual angle selection. The approach provides a practical alternative to elaborate and time consuming beam angle optimization schemes and is suitable for routine clinical usage.

[Posttraumatic dystonia. Review and legal aspects]. / Die posttraumatische Dystonie. Ein Uberblick und gutachterliche Aspekte.

More attention should be paid to dystonia as a consequence of trauma, particularly with regard to legal aspects. The underlying pathophysiological mechanisms of dystonia following central or peripheral trauma are largely unknown. Hemidystonia after severe head trauma is regarded to be due to contralateral basal ganglia lesions, particularly of the putamen. Focal and segmental dystonias follow various kinds of peripheral trauma. Central synaptic reorganisation due to altered peripheral input may play a role in its genesis. Clinically, post-traumatic dystonia differs from the idiopathic disease by the presence of accompanying pain or causalgia, limitation of the range of movement up to fixed posture, and poor response to conventional pharmacotherapy. If an expert opinion is requested, it is important to ascertain the diagnosis clinically and by EMG. To establish the cause-and-effect relationship between trauma and movement disorder, the severity of the injury, time course, and anatomical relationship must be taken into consideration.

Prism: a new approach to radiotherapy planning software.

PURPOSE: We describe the capabilities and performance of Prism, an innovative new radiotherapy planning system with unusual features and design. The design and implementation strategies are intended to assure high quality and clinical acceptability. The features include Artificial Intelligence tools and special support for multileaf collimator (MLC) systems. The design provides unusual flexibility of operation and ease of expansion. METHODS AND MATERIALS: We have implemented Prism, a three-dimensional (3D) radiotherapy treatment-planning system on standard commercial workstations with the widely available X window system. The design and implementation use ideas taken from recent software engineering research, for example, the use of behavioral entity-relationship modeling and the "Mediator Method" instead of ad-hoc programming. The Prism system includes the usual features of a 3D planning system, including Beam's Eye View and the ability to simulate any treatment geometry possible with any standard radiotherapy accelerator. It includes a rule-based expert system for automated generation of the planning target volume as defined in ICRU Report 50. In addition, it provides special support for planning treatments with a multileaf collimator (MLC). We also implemented a Radiotherapy Treatment Planning Tools Foundation for Prism, so that we are able to use software tools form other institutions without any source code modification. RESULTS: The Prism system has been in clinical operation at the University of Washington since July 1994 and has been installed at several other clinics. The system is run simultaneously by several users, each with their own workstation operating from a common networked database and software. In addition to the dosimetrists, the system is used by radiation oncologists to define tumor and target volumes and by radiation therapists to select treatment setups to load into a computer controlled accelerator. CONCLUSIONS: Experience with the installation and operation has shown the design to be effective as both a clinical and research tool. Integration of software tools has eased the development and significantly enhanced the clinical usability of the system. The design has been shown to be a sound basis for further innovation in radiation treatment planning software and for research in the treatment planning process.

Evaluation of an expert system producing geometric solids as output.

This paper reports the evaluation of an expert system whose output is a three-dimensional geometric solid. Evaluating such an output emphasizes the problems of establishing a comparison standard, and of identifying and classifying deviations from that standard. Our evaluation design used a panel of physicians for the first task and a separate panel of expert judges for the second. We found that multi-parameter or multi-dimensional expert system outputs, such as this one, may result in lower overall performance scores and increased variation in acceptability to different physicians. We surmise that these effects are a consequence of the higher number of factors which may be deemed unacceptable. The effects appear, however, to be equal for computer and human output. This evaluation design is thus applicable to other expert systems producing similarly complex output.

Treatment of adenoid cystic carcinoma of the salivary gland, a three-field technique.

Clinical trials have demonstrated that fast neutron radiotherapy is the treatment of choice for advanced inoperable salivary gland tumors. A three-field technique utilizing a medically dedicated cyclotron to produce fast neutrons is described for the treatment of adenoid cystic carcinoma of the parotid. This three-field technique utilizes the cyclotron's multi-leaf collimator system to treat large asymmetric fields, which spare normal tissues otherwise treated with conventional wedged pair techniques. Field geometry, field weightings, and beam normalization will be discussed in relation to this three-dimensional treatment volume.