Patent Number: 051608472
Section: summary

INTRODUCTION AND BACKGROUND This invention relates to a dynamic multivane electron arc beam collimator and a dynamic multivane electron arc beam collimation system and related apparatus and methods. The invention is useful in connection with electron arc therapy, which is an electron radiation treatment method used to treat cancer. For example, electron arc therapy is used to treat a patient's chest wall following a mastectomy. The practice of electron arc therapy requires an electron source to provide the electron beam (electron radiation) which is used to treat the target area of the patient. A linear accelerator can be the electron source. A purpose of the invention is to improve the uniformity of dose delivered to a large treatment surface during the technique of electron arc therapy. Dosimetric studies (as detailed in the attached publications list) have shown that an improvement in electron arc therapy dose uniformity can be achieved through application of this invention. A collimator is used in combination with the linear accelerator to define the shape of the electron field of the electron beam. The shape of the electron field is defined by the collimator's electron aperture. The head of the linear accelerator is moved through or along an arc of rotation above the patient as the electron beam is emitted through the head and collimator to the target area (i.e. treatment area) of the patient. Such movement is referred to herein as "linear accelerator rotation." It is desired that the electron dose be uniform across the target area and that electron radiation to patient areas outside of the target area be minimized. The following publications include information relevant to an understanding of the invention: 1. Leavitt, D. D., Peacock, L. M., Gibbs, F. A., and Stewart, J. R.: "Electron Arc Therapy: Physical Measurement and Treatment Planning Techniques" Int. J. Radiation Oncology Biol. Phys., Vol. 11, pp. 987-999 (May, 1985). PA1 2. McNeely, L. K., Jacobson, G. M., Leavitt, D. D., and Stewart, J. R.: "Electron Arc Therapy: Chest Wall Irradiation of Breast Cancer Patients" Int. J. Radiation Oncology Biol. Phys., Vol. 14, pp. 1287-1294 (June, 1988). PA1 3. Leavitt, D. D. and Stewart, J. R.: "Optimization of Electron Arc Therapy Doses by Dynamic collimator Control" Proceedings of the 9th International Conference on the Use of Computers in Radiation Therapy, pp. 149-152, June 1987. PA1 4. Leavitt, D. D., Stewart, J. R. Moeller, J. H., and Earley, L.: "Optimization of Electron Arc Therapy Doses by Multi-vane Collimator Control" Int. J. Radiation Oncology Biol. Phys., Vol. 16, pp. 489-496 (February, 1989). This paper was presented at the 29th Annual Meeting of the American Society of Therapeutic Radiology and Oncology, Oct. 20, 1987, Boston, Mass. PA1 5. Leavitt, D. D.: "Multileaf Collimation in Electron Arc Therapy". This paper was presented on May 3, 1988 at the Proceedings of the Twelfth Varian User's Meeting. PA1 6. Leavitt, D. D., Stewart, J. R., Moeller, J. H., Lee, W. L., and Takach, Jr. G. A.: "Electron Arc Therapy: Design, Implementation and Evaluation of a Dynamic Multi-vane Collimator System". This paper was presented at the 30th Annual Meeting of the American Society of Therapeutic Radiology and Oncology, Oct. 11, 1988. Accepted for publication in International Journal of Radiation Oncology Bio. Phys. February, 1989. Copies of the above-identified publications are filed with this patent application and are incorporated by reference into this specification. Through the innovations of our invention it is possible to design and construct a dynamic multivane electron arc beam collimator that is attachable to the head of a linear accelerator. These innovations contribute to the ease of use of the collimator and reduce the complexity and size of the collimator without reduction of functionality or features. These innovations facilitate collimator installation and eliminate or reduce the need to modify the linear accelerator. SUMMARY OF THE INVENTION This invention is a dynamic multivane electron arc beam collimator and a dynamic multivane electron arc beam collimation system. In one form of this invention, the dynamic multivane electron arc beam collimator includes a plurality of collimation vanes, a plurality of vane movement means associated with the vanes and a plurality of local controllers at the collimation site. The vanes are positioned and adapted to define an electron aperture which defines the electron field of the electron beam emitted by the linear accelerator. The vane movement means move the vanes to dynamically define the electron aperture. The local controllers control the vane movement means. Vane movement is independent of the movement of the other vanes and is capable of movement simultaneous with the movement of other vanes. In another form of this invention, the collimator includes a plurality of collimation vanes, a means for moving said vanes, and local controllers (i.e. local intelligence) at the collimation site for controlling the vane movement means. Other aspects of this invention provide to the collimator a local power source (e.g. battery) at the collimation site, a noncontact communications means (e.g. infra-red transceiver), and a network for communication between the local processors (and any other network resident nodes such as the host controller). The elements of the collimator, i.e., the vanes, vane movement means and local controller(s) together with any local power source or noncontact communications means, can be combined to form a unit that is attachable to, and detachable from, the linear accelerator. In another form of this invention the inventive collimator is part of a dynamic multivane electron arc beam collimation system which further includes: (i) means for selecting a treatment arc and for dividing the treatment arc into a plurality of arc segments defined by reference angles, (ii) means for determining preferred vane pair openings for each arc segment and for representing said preferred vane pair openings as vane position data for each arc segment; (iii) means for monitoring current treatment angle of the linear accelerator during linear accelerator rotation to detect reference angles when encountered by such rotation, and (iv) means for sequentially transmitting to the local controllers of the collimator the vane position data of each arc segment when the reference angle identifying the arc segment is encountered by linear accelerator rotation. The local controllers of the collimator are adapted to process the vane position data received by the local controllers. The local controllers and vane movement means are adapted to cause the vanes to move to the vane positions represented by the vane position data of the arc segments as transmitted to the local controllers during linear accelerator rotation. An innovation of this invention is the use of distributed processing as applied to the local controllers of the collimator. A plurality of local controllers is used instead of a single controller at the collimator site. The sum of the complexities and size requirements of a plurality of local controllers for controlling a given number of vanes (or vane movement means) is less than the complexity and size requirement of a single controller for controlling the same number of vanes (or vane movement means). By using a plurality of local controllers the collimator is less complex and smaller than would otherwise be the case. These characteristics contribute to the design and construction of a collimator that can attachable to and detachable from the head of a linear accelerator. An innovation of this invention is the concept of a dynamic electron beam collimator that is attachable to and detachable from the head of a linear accelerator. Small size and light weight of the collimator make such attribute practicable. Because the collimator of this invention is only intended for electron arc therapy it only needs to be exposed to radiation in the treatment room during its use as an electron arc therapy collimator. When not in use, the collimator can be detached from the linear accelerator and removed from the treatment room to avoid radiation damage to the collimator electronics during other radiation treatment processes. Because of this limited exposure, the collimator does not require the large amount of shielding that would be needed to protect its electronics against the kinds and quantities of radiation that it would necessarily be exposed to if the collimator was permanently attached to the linear accelerator or attached in such a way that it would not be practicable or easy to remove the collimator from the linear accelerator during nonuse. The practice of removing the collimator (which is practicable only if the collimator is removable and portable) to protect it against excessive radiation allows for the use of local intelligence (local controllers) in the collimator to control and monitor vane movement. An innovation of this invention is the concept of a dynamic multivane electron arc beam collimator that can be used as an accessory to a linear accelerator without the need for modification of the linear accelerator. For example, the collimator can be attached to a conventional linear accelerator by attachment to the standard accessory mount assembly as if the collimator were an accessory tray compatible with the accessory mount assembly of the linear accelerator. Thus, the dynamic collimator can be attached to any linear accelerator in the same manner as fixed collimation plates and blocks. An innovation of this invention is the concept of a dynamic multivane electron arc beam collimator that can be operated independent of any electrical connection to the linear accelerator. The collimator can function as a self-contained unit independent of the electronics of the linear accelerator. This simplifies the task of installing the collimator and/or retrofitting the linear accelerator for use with the dynamic collimator. An innovation of this invention is the application of local intelligence (local controllers) to the dynamic collimator at the collimation site. This contributes simplicity of use and facilitates after market installation to linear accelerators. Local intelligence at the collimation site eliminates the need for connections (e.g. cables) to a remote source of intelligence (i.e., a remote controller). Local intelligence also allows device function verification and testing to be performed prior to any treatment cycle. An innovation of this invention is the concept of a local power source (e.g. battery) at the dynamic collimation site. This eliminates the need for connections (e.g. cables) to a remote power source. An innovation of this invention is the concept of noncontact communication between the local controllers at the dynamic collimation site and a collimator controlling host computer. This eliminates the need for physical connections (e.g. cables or wiring) running from the dynamic collimator to the collimator controlling host computer. This simplifies the task of installing the collimator and/or retrofitting the linear accelerator for use with the dynamic collimator. An innovation of this invention is the concept of applying network communications to the local controllers at the dynamic collimation site and the other intelligent devices (e.g., host controller, display monitors, etc.). The use of a network (e.g. token passing network) for communications facilitates the addition of additional vanes, sensors, controllers, monitors and other devices that may be desired by the user. The above-identified innovations are included in the embodiment of this invention described in detail below but such innovations and this invention are not limited to such embodiment. This invention further includes the other innovations, improvements and novel apparatus and methods disclosed elsewhere in this disclosure and/or the accompanying drawings.