Patent Number: 058959262
Section: summary

FIELD OF THE INVENTION The present invention generally relates to control and security systems for radiation treatment facilities. In particular, the invention pertains to beamline control and security systems for proton therapy facilities and to systems for controlling, detecting and preventing hazardous conditions to patients, personnel and facility apparatus. BACKGROUND OF THE INVENTION Contemporary radiation therapy utilizes several types of ionizing radiation, such as .beta.-rays, .gamma.-rays, X-rays and high-energy protons applied to malignant tissue to prevent and control the spread of cancer. Proton beam therapy, in particular, has undergone dramatic development in recent years with attendant advances in therapy techniques and facilities. In most proton therapy systems around the world, the proton accelerators were originally built for physics research and later adapted for part-time clinical research and therapy. However, the imminent advantages of proton beam therapy is best realized with the development of dedicated, clinically based facilities. One such therapy facility, located at the Loma Linda University Medical Center, was purposely built to provide therapeutic proton beams to a multiplicity of treatment rooms, thereby increasing patient throughput and defraying the cost of an otherwise expensive form of treatment. An overview of the facility and its development is provided in "The Proton Treatment Center at Loma Linda University Medical Center: Rationale for and Description of its Development," J. M. Slater, et al., Intl. J. Radiation Oncology, vol. 22, no. 2, 1992, pp.383-389, and herein incorporated by reference. A more detailed description of the proton beam apparatus and facility is provided in U.S. Pat. No. 4,870,287 by F. T. Cole, et al., entitled "Multi-Station Proton Beam Therapy System," also herein incorporated by reference. Proton radiation beamlines operate using large high-field electromagnets for beam deflection and focussing. At the Loma Linda Facility, the proton beam is generated with an on-site proton synchrotron and transferred by such beamlines to any one of several target destinations. To insure protection from proton radiation exposure, the beamline magnets must be monitored and controlled to prevent beam misdirection and mistiming. To this end, a method of treatment room selection verification has been employed by which a selected or desired beam path implementation is verified before authorizing beam delivery. The method of selection verification is more fully disclosed in U.S. Pat. No. 5,260,581, herein incorporated by reference. While such a method appears to be a necessary safeguard from radiation misexposure, it does not detect all potentially hazardous fault conditions. The collection of such magnets often require megawatts of electrical power, which itself presents a lethal hazard to facility personnel if appropriate safeguards are not taken to insure personnel non-contact. Thus, in addition to properly coordinating and timing the magnet array, appropriate measures should be taken to insure against mechanical, electrical and thermal breakdown. In the event of component failure, by any means, the high-power apparatus should be disabled and the radiation beam directed to a so-called "beam dump." Clearly, meeting these challenging demands is a necessity of great importance. In the broader context of radiation therapy, a necessary precondition for treatment is the safeguard of patients and personnel from accidental radiation exposure. In particular, at proton beam treatment facilities, accidental exposure to beam radiation or derivatives thereof is perceived to be the principal threat to patient and personnel safety. Inadvertent exposure to radiation may for example occur through beam misdirection or improper timing of radiation beam delivery. Nevertheless, as the demand for proton beam therapy increases and treatment facilities become more complex, as for example at the Loma Linda University Medical Center, beamline safety becomes a premium and the challenge of insuring beamline safety is taken very seriously. SUMMARY OF THE INVENTION A preferred radiation treatment facility in accordance with the present invention basically comprises a radiation beam source, a plurality of radiation beam treatment locations, and a multiplexed switchyard and beam transport system for directing the radiation beam to a selected one of the radiation beam treatment locations. One potential problem associated with such a treatment facility is the possibility of accidental radiation exposure through wrong-path or multiple path activation. Thus, it is one object of the present invention to safeguard against accidental radiation exposure, as well as other hazardous conditions for personnel and apparatus. In accordance with one aspect of the present invention, a method of radiation beam security comprises first receiving a beam request signal from a selected treatment location. A beam path configuration signal is derived from the beam request signal and used to select the switchyard and beam transport system configuration. The configuration of the switchyard and beam transport system is sensed to verify that the switchyard and beam transport system configuration allow radiation beam transport to the selected treatment location and no other. Upon verification of correct system configuration, radiation beam transport is provided to the selected treatment location. Because there is a plurality of available beam paths, it is not only necessary to check that the selected path is activated, but preferably also that no additional beam paths are simultaneously active. The method of the present invention accomplishes this verification by deriving a switchyard and beam transport system configuration signal from the sensing procedure. The switchyard and beam transport system configuration signal is compared to the selected beam path configuration signal. This comparison entails verifying that every element of the selected beam path configuration signal is contained in the switchyard and beam transport system configuration signal, thus insuring that the selected path has been activated. The comparison further entails verifying that every element of the switchyard and beam transport configuration signal is contained in the selected beam path configuration signal, hence also insuring that no additional path is activated. In addition to path configuration sensing, a preferred beamline control and security system safeguards against other hazardous conditions for personnel and apparatus such as electrocution, apparatus overheating and communication link failures. Sensing is preferably also performed to detect potential human contact with electrical load bearing components which may pose a threat of electrocution. Furthermore, sensing is preferably performed to detect over heating by electrical load bearing components. Communication failures are reduced by providing redundant communication paths for sensed information as well as signal processing steps. When redundant communication paths are mutual logical complements, their logical comparison provides a method to determine a communication link failure. In accordance with another aspect of the present invention, an apparatus for radiation beam security comprises a means for receiving a beam request signal from a selected treatment location and a means for deriving a beam path configuration signal from said beam request signal, such as for example a digital signal communication network and local digital processor. The apparatus also comprises a means for selecting the switchyard and beam transport system configuration based on the selected beam path configuration signal. Furthermore, there is a means for sensing the configuration of the switchyard and beam transport system to verify that the switchyard and beam transport system configuration allow radiation transport to only the selected treatment location. Finally, there is means for providing radiation beam transport to the selected treatment location, in response to the aforementioned verification. In accordance with another aspect of the present invention, an apparatus for controlling the multiplexed switchyard and beam transport system comprises a plurality of groups comprising elements of the multiplexed switchyard and beam transport system, wherein each group has a common functional characteristic different from the other groups. The apparatus further comprises a dedicated controller for each of the groups having a common functional characteristic. Preferably, each group comprises elements having a common functional characteristic pertaining to the transport of radiation to each of the plurality of radiation beam paths. Furthermore, preferably each dedicated controller operates to activate the respective functional elements for the selected beam path.