Integration of radiotherapy planning systems and radiotherapy treatment equipment: 11 years experience.

PURPOSE: We have investigated the requirements, design, implementation, and operation of a computer-controlled medical accelerator with multileaf collimator (MLC), integrated with a radiation treatment-planning system (RTPS), and we report on the performance, benefits, and lessons learned from this experience. METHODS AND MATERIALS: In 1984 the University of Washington installed a computer-controlled radiation therapy machine (the Clinical Neutron Therapy System, or CNTS) with a multileaf collimator. Since the beginning of operation the control system computer has been connected by commercially available network hardware and software to three generations of radiation treatment-planning systems. Semiautomated setup and completely computerized check and confirm were incorporated into the system from the beginning of clinical operation in 1984. The system cannot deliver a patient treatment without a computer-prepared treatment plan. RESULTS: The CNTS has been in use for routine patient treatments for over 11 years. The cost of the network connection and software was an insignificant fraction of the facility cost. Operation has been efficient and reliable. Of the 441 machine-related session reschedulings (out of 18,432 sessions total) during the past 9 years, only 20 were due to problems with data transfer between the RTPS and CNTS, associated primarily with two incidents. Close integration with the treatment-planning system allows complex treatments to be delivered. Dramatic evolution of the departmental treatment-planning system has not required any changes or redesign of either the accelerator control system or the network connection. CONCLUSIONS: Our experience shows that a large degree of automation is possible with reasonable effort, by using well-known software and hardware design strategies. The lessons we have learned from this can be carried over into photon therapy now that photon accelerators with MLC facilities are commercially available.

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.

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.

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.

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.

Left ventricular performance in endotoxin shock in dogs.

Endotoxin shock, with maximal velocity of contraction (Vmax) as our index of contractility, showed no myocardial depression in an earlier 4-h study (Guntheroth, Proc. Soc. Exp. Biol. Med. 157: 610--614, 1978). Because of reports of late deterioration, we studied six dogs until spontaneous death (9--18 h). Heart rate nearly doubled and left ventricular filling pressure and aortic mean pressure fell, but Vmax did not change significantly. Because of concern that the marked increase in heart rate may have contributed to an artifactual maintenance of Vmax (due to its frequency dependence, inherent in dp/dt), we studied a final group of five dogs with three additional indicators of contractility. End-systolic pressure-diameter ratio (Emax), ejection fraction (sonar-determined from the minor axis of the left ventricle), and frequency-normalized average rate of generation of power density (FARPD) all fell early and remained low until death. We conclude that myocardial contractility is significantly reduced in endotoxin shock, early and sustained. Its presence is masked somewhat in the untreated subject by the reduced work load, secondary to hypovolemia.

A research-oriented treatment planning program system.

The function of a treatment planning program is to graphically simulate radiation dose distribution from proposed radiation therapy treatments. While many such programs are available which provide this much-needed service, none addresses the question of how to compare calculation and display techniques. This paper describes a program system described for support of research efforts, particularly development and testing of new calculation algorithms. The system emphasizes a modular flexible structure, enabling programs to be developed somewhat as interchangeable parts. Thus multiple variants of a calculation algorithm can be compared without undue software overhead or additional data management. Unusual features of the system include extensive use of command procedures, logical names and a structured language (PASCAL). These features are described along with other implementation details. Obstacles, limitations and future applications are also discussed.

Barometric measurement of tidal volume: effects of pattern and nasal temperature.

The accuracy of the formula derived by Drorbaugh and Fenn (Pediatrics 16: 81-86, 1955) for calculating tidal volume (VT) from the phasic pressure change measured when an animal breathes in a closed chamber has recently been challenged. Epstein and Epstein (Respir. Physiol. 32: 105-120, 1978) argue that the formula may underestimate VT by up to 30% and predict that the error increases as the ratio of inspiratory duration (TI) to total breath duration (Ttot) increases, and as the expired temperature at the nares (TN) increases. To test their theory, I measured VT in anesthetized rats by the barometric technique and by conventional pneumotachography simultaneously. TN was varied from ambient to body temperature by passing a variable current through the pneumotachograph heater; TI/Ttot was varied by changing FICO2 and by selecting different rats. The predictions were confirmed. A factor is derived for retrospectively correcting VT estimated by the Drorbaugh-Fenn formula. It requires knowledge of TN and TI/Ttot and reduces the error between experiments to under 20% and within each experiment to about 5%. To facilitate its use, TN was measured in rat, rabbit, cat, man, and infant pigtail monkey.

A plethysmograph for long-term measurements of ventilation in unrestrained animals.

An apparatus for quantitative measurement of ventilation in unrestrained small animals is described. The subject rests in an environmental chamber, and respiration is indicated by barometric pressure oscillations proportional to tidal volume. The chamber is purged continuously at a relatively high flow rate during studies. Thus, CO2 does not accumulate and long-term measurement can proceed without interruption. Respiratory control studies are especially facilitated since different gas mixtures can be rapidly passed through the chamber. An electronic device also is described which automatically calculates expired minute volumes (VE) from the pressure signal obtained from the plethysmograph.