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Some of the useful clinical radiation characteristics required for treatment planning using the 6,9,13,17, and 20 Me V scanning electron beams obtainable in a CGR Therac-20 Me V Saturne linear accelerator are outlined.
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The fundamental principles of construction, the operational data, handling and safety devices of the first linear electron accelerator type Therac 20-Saturne (CGR MeV) installed in Germany are described. Relevant characteristics of the radiation field for therapy with 12 and 18-MV photons and also the dosimetric data are reported. Observance of the tolerances recommended by the IEC is guaranteed with this accelerator.
The conception of radiosurgery now more than 40 years old is realized in clinical practice during last 25 years. There were elaborated 3 main methods: focused irradiation by gamma knife, by accelerated heavy charged particles and by linear accelerator. The results led radiosurgery spread over the world. The main indications are vascular malformations (44%), benign intracranial tumours (33%), malignant tumours including metastasis (21%) and functional disorders (2%). The pathological lesions can be controlled or liquidated in 80-95%. The hospital story is minimal, 1-2 days, and there is no risk of mortality and morbidity is minimal. Only the time of healing is prolonged to some years with indispensable follow-up. Further technical improvement and growing number of patients treated by radiosurgery can be expected.
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A metal-resin composite material was experimentally prepared by mixing a powder consisting of Ag-Cu particles and BPO with a paste consisting of UDMA-based monomer and 4-META in the absence of tertiary amine. The working time and setting time were mainly affected by the amounts of 4-META, BPO and metal particles, most of them fulfilling the requirements for working time and setting time specified in ISO 4049:2000 in the present experimental conditions. The flexural strength ranged from 49.6 MPa to 77.8 MPa, and the highest value was obtained when the 4-META concentration was high and metal particle content was low. The flexural modulus of elasticity, ranging from 6.7 GPa to 11.9 GPa, significantly increased as the 4-META concentration and metal particle content increased. Based on its mechanical properties, this metal-resin composite in which metal particles are involved in the polymerization initiation system has the potential to be used as a dental restorative material.
An etched-track method was applied for a measurement of the effective dose of natural background neutrons. Ten assemblies of polycarbonate film and 10B were placed at the center of a rem-counter type moderator. The assemblies were put in an air-tight container in order to avoid a continuous contribution from radon. Electrochemical etching was adopted. The sensitivity of the detector was 0.21 +/- 0.02 microSv pit(-1) cm2. After a period of storage of 4.3 y, the number of recorded artifact pits in the films corresponded to an effective dose rate of 0.8 +/- 0.2 microSv y(-1). The effective dose rate of natural background neutrons was 18.1 +/- 3.6 microSv year(-1) for the same period, with an artifact dose being subtracted. The total net number of etched-track pits of the present detector was 75 +/- 15 when used for measuring an effective dose of natural background level neutrons for 1 mo, which gives enough counting statistics. The method can thus be applied for monitoring the effective dose of neutrons around nuclear sites and high-energy accelerator facilities.
The operational radiation protection issues associated with the Z-Machine accelerator located at Sandia National Laboratories are large: a variety of materials can be placed into the machine; these materials can be subjected to a variety of nuclear reactions, producing a variety of activation products. Without full understanding of the most likely contaminants, a realistic identification of the radiological hazards and appropriate controls is not possible. This paper presents a process developed to provide a realistic prediction of the accelerator-produced radionuclides of interest.