PubMed Health⌕ Search

Biomedical subjects

I J Kalet

Publications and source records attributed to I J Kalet.

7 recordsLinked to original sources
PubMed1990

Knowledge-based computer systems for radiotherapy planning.

Radiation therapy is one of the first areas of clinical medicine to utilize computers in support of routine clinical decision making. The role of the computer has evolved from simple dose calculations to elaborate interactive graphic three-dimensional simulations. These simulations can combine external irradiation from megavoltage photons, electrons, and particle beams with interstitial and intracavitary sources. With the flexibility and power of modern radiotherapy equipment and the ability of computer programs that simulate anything the machinery can do, we now face a challenge to utilize this capability to design more effective radiation treatments. How can we manage the increased complexity of sophisticated treatment planning? A promising approach will be to use artificial intelligence techniques to systematize our present knowledge about design of treatment plans, and to provide a framework for developing new treatment strategies. Far from replacing the physician, physicist, or dosimetrist, artificial intelligence-based software tools can assist the treatment planning team in producing more powerful and effective treatment plans. Research in progress using knowledge-based (AI) programming in treatment planning already has indicated the usefulness of such concepts as rule-based reasoning, hierarchical organization of knowledge, and reasoning from prototypes. Problems to be solved include how to handle continuously varying parameters and how to evaluate plans in order to direct improvements.

Artificial Intelligence↗
PubMed1987

A comparison of two radiological path length algorithms.

Most radiation therapy dose calculation methods require the determination of the effective path length of the primary radiation from the radiation source to the point at which the dose is calculated. This usually involves representing the patient anatomy as a set of polygons (contours) as approximations to plane curves. Several algorithms are known for determining the length of a segment or segments on a ray through a planar contour, that are interior to the contour. We have implemented two of these algorithms in a test program to benchmark their relative efficiency. One algorithm uses a linear search over all the contour segments, and the other method represents the contour as a binary tree of "strips," of successively increasing resolution. In general, the tree search should give times proportional to log(n) where n is the number of contour segments, and the linear search time should be proportional to n. Thus, one might expect the tree search to run faster once the number of segments reaches some sufficiently large value. We found that this value is a number of contour points far in excess of that typical for contours representing radiation therapy patient anatomy. Therefore, for this application the linear search method is more efficient.

Algorithms↗
PubMed1986

Radiotherapy planning: direct tumor location on simulation and port films using CT. Part I. Principles.

Although there have been great advances in cancer diagnosis in recent years, it remains difficult to transfer tumor location information from cross-sectional computed tomographic (CT) scans or magnetic resonance images to the simulation and verification films used in planning radiotherapy. A newly developed system uses radioopaque markers attached to the patient as reference points. These markers are identified on both CT scans and simulation films and their locations entered into the treatment planning computer. The tumor and any desired normal structures are then outlined manually on each CT section. Transparent overlays produced by the computer show the position of the reference markers and tumor outlines for any combination of gantry angles and source-film distance. Because the overlays are scaled to the simulation films, the reference points enable precise alignment of overlay and film. The tumor outline thus appears on the simulation or verification films exactly as it is "seen" by the therapy beam, making field verification straightforward and accurate, even on oblique films.

Adult↗
PubMedDate not supplied

Radiation therapy treatment planning using concurrent programming.

Concurrent programming can be applied to the problem of computer graphic simulation of radiation treatment of tumors (radiation treatment planning). Running several tasks or programs simultaneously on behalf of a single user provides a big improvement over the traditional sequential approach, in which editing a treatment plan and computing and displaying dose distributions are separate operations which must be invoked by explicit commands. With our system, the user sees isodose contours being updated automatically and continuously as the plan is edited; this greatly facilitates plan optimization. The complexity of parallel processing has resulted in a 'conventional wisdom' which discourages this technique. The usual approach is to have parallel processes share a common global data structure, which makes interaction hard to control and discourages modularity and data abstraction. We have developed an alternative approach based on message streams which instead enhances modularity and data abstraction while still providing the advantages of parallel processing. The system is very reliable and is used routinely in a practical clinical environment.

Computer Simulation↗
PubMedDate not supplied

How to draw irregular radiation beams in 3-D treatment plans.

We describe a general method for computing the outline which an irregular field originating from some arbitrary angle makes on a plane which may be oriented obliquely within the patient. We describe the mathematical theory of the method, which is based on coordinate transformations expressed as matrix multiplications. Then we describe the implementation of the method in the Pascal programming language, emphasizing language-independent optimizations which ensure fast interactive response. Finally, we describe a systematic program testing procedure that is derived from the mathematical theory, which improves our confidence that the method is coded correctly.

Computer Graphics↗