Ruedi Risler

Modification of the University of Washington Neutron Radiotherapy Facility for optimization of neutron capture enhanced fast-neutron therapy

A modified neutron production target assembly has been developed to provide improved performance of the proton-cyclotron-based neutron radiotherapy facility at the University of Washington for applications involving neutron capture enhanced fast-neutron therapy. The new target produces a neutron beam that yields essentially the same fast-neutron physical depth-dose distribution as is produced by the current UW clinical system, but that also has an increased fraction of BNCT enhancement relative to the total therapeutic dose. The modified target is composed of a 5-millimeter layer of beryllium, followed by a 2.5-millimeter layer of tungsten, with a water-cooled copper backing. Measurements of the free-field neutron spectrum of the beam produced by the new target were performed using activation foils with a direct spectral unfolding technique. Water phantom measurements were performed using a tissue-equivalent ion chamber to characterize the fast-neutron depth-dose curve and sodium activation in soda-lime glass beads to characterize the thermal-neutron flux (and thus the expected neutron capture dose enhancement) as a function of depth. The results of the various measurements were quite consistent with expectations based on the design calculations for the modified target. The spectrum of the neutron beam produced by the new target features an enhanced low-energy flux component relative to the spectrum of the beam produced by the standard UW target. However, it has essentially the same high-energy neutron flux, with a reduced flux component in the mid-range of the energy spectrum. As a result, the measured physical depth-dose curve in a large water phantom has the same shape compared to the case of the standard UW clinical beam, but approximately twice the level of BNCT enhancement per unit background neutron dose at depths of clinical interest. In-vivo clinical testing of BNCT-enhanced fast-neutron therapy for canine lung tumors using the new beam was recently initiated.

Experience with Z Developing a Control Program for a Radiation Therapy Machine

We are developing a control program for a unique radiation therapy machine. The program is safety-critical, executes several concurrent tasks, and must meet real-time deadlines. Development employs both formal and traditional methods: we produce an informal specification in prose (supplemented by tables, diagrams and a few formulas) and a formal description in Z. The Z description includes an abstract level that expresses overall safety requirements and a concrete level that serves as a detailed design, where Z paragraphs correspond to data structures, functions and procedures in the code. We validate the Z texts against the prose specification by inspection. We derive most of the code from the Z texts by intuition and verify it by inspection but a small amount of code is derived and verified more formally. We have produced about 250 pages of informal specification and design description, about 1200 lines of Z and about 6000 lines of code. Experiences developing a large Z specification and writing the program are reported, and some errors we discovered and corrected are described.

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.

Control system specification for a cyclotron and neutron therapy facility

A comprehensive specification for the computer control system of a cyclotron and treatment facility that provides particle beams for cancer treatments for fast neutrons, production of medical isotopes, and physics experiments is discussed. The control system is described as thoroughly as is practical using standard technical English, supplemented by tables, diagrams, and algebraic equations. This specification comprises over 300 single-spaced pages. A more precise and compact specification might be achieved by making greater use of formal mathematical notations instead of English. Work has begun on a formal specification of the system, using the Z and Petri net notations.<<ETX>>

University of Washington Clinical Neutron Facility: Report on 26 Years of Operation

Particle radiotherapy facilities are highly capital intensive and must operate over decades to recoup the original investment. We describe the successful, long‐term operation of a neutron radiotherapy center at the University of Washington, which has been operating continuously since September 1984. To date, 2836 patients have received neutron radiotherapy. The mission of the facility has also evolved to include the production of unique radioisotopes that cannot be made with the low‐energy cyclotrons more commonly found in nuclear medicine departments. The facility is also used for neutron damage testing for industrial devices. In this paper, we describe the challenges of operating such a facility over an extended time period, including a planned maintenance and upgrade program serving diverse user groups, and summarize the major clinical results in terms of tumor control and normal tissue toxicity. Over time, the mix of patients being treated has shifted from common tumors such as prostate cancer, lung c...

Boron neutron capture (BNC): a mechanism for enhancing tumor cell kill in fast neutron radiotherapy

At therapeutic doses fast neutron radiotherapy alone gives significant tumor control can result in a significant increase in tumor control probability. As a fast neutron beam penetrates tissue it is partially moderated producing a cloud of thermalized neutrons. We describe measurements of this thermalized component using the therapy beam at the University of Washington and show how it is possible to increase its magnitude without appreciable degradation of the other clinical properties of the beam. We describe model calculation of the radiobiological effects of a boron neutron capture boost as well as in vitro cell culture measurements on the V-79 cell line, in vivo experiments on the 36B10 rat glioma system, and a preliminary experiment on a human melanoma nodule test system. Plans to extend this work to clinically-relevant tumor systems are discussed.

Relational database: a radiation therapy machine control software development tool

A relational database is being used to develop control software for a neutron radiation therapy system including a cyclotron and an isocentric treatment gantry. The control system entails over 1000 input and output signals. Signal descriptions and internal control system parameters are stored in a relational database. Database queries can generate design documents, answer ad-hoc inquiries about signals, and create machine-readable tables used by control-system computer programs. Engineering staff can reconfigure the control system by updating the database without modifying the control system executable software.<<ETX>>

Routine operation of the University of Washington fast neutron therapy facility and plans for improvements

The fast neutron therapy facility in Seattle is based on a cyclotron, which produces a 50.5 MeV proton beam. Neutrons are produced in a beryllium target installed in an isocentric gantry equipped with a multi-leaf collimator. The system has been in routine operation for 14 years and over 1800 patients have been treated. Downtime has been minimal, over the past 10 years less than 1.5% of the scheduled daily treatment sessions could not be delivered for equipment related reasons. Fast neutron therapy has been shown to be highly effective for the treatment of salivary gland tumors, sarcomas of bone and soft tissues and for certain prostate cancers. In addition there are situations such as non-small cell lung cancer, where results are promising, but success is limited by normal tissue complications. A relatively small selective increase in the tumor dose might lead to a significant clinical improvement in these situations. The use of a boron neutron capture (BNC) boost, utilizing the moderated slow neutrons n...