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Most accelerator-based space radiation experiments have been performed with single ion beams at fixed energies. However, the space radiation environment consists of a wide variety of ion species with a continuous range of energies. Due to recent developments in beam switching technology implemented at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL), it is now possible to rapidly switch ion species and energies, allowing for the possibility to more realistically simulate the actual radiation environment found in space. The present paper discusses a variety of issues related to implementation of galactic cosmic ray (GCR) simulation at NSRL, especially for experiments in radiobiology. Advantages and disadvantages of different approaches to developing a GCR simulator are presented. In addition, issues common to both GCR simulation and single beam experiments are compared to issues unique to GCR simulation studies. A set of conclusions is presented as well as a discussion of the technical implementation of GCR simulation.

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Proton beams offer several advantages over conventional radiation techniques for treating cancer and other diseases. These advantages might be negated if the leakage and scatter radiation from the beamline and patient are too large. Although the leakage and scatter radiation for the double scattering proton beamlines at the Loma Linda University Proton Treatment Facility were measured during the acceptance testing that occurred in the early 1990s, recent discussions in the radiotherapy community have prompted a reinvestigation of this contribution to the dose equivalent a patient receives. The dose and dose equivalent delivered to a large phantom patient outside a primary proton field were determined using five methods: simulations using Monte Carlo calculations, measurements with silver halide film, measurements with ionization chambers, measurements with rem meters, and measurements with CR-39 plastic nuclear track detectors. The Monte Carlo dose distribution was calculated in a coronal plane through the simulated patient that coincided with the central axis of the beam. Measurements with the ionization chambers, rem meters, and plastic nuclear track detectors were made at multiple locations within the same coronal plane. Measurements with the film were done in a plane perpendicular to the central axis of the beam and coincident with the surface of the phantom patient. In general, agreement between the five methods was good, but there were some differences. Measurements and simulations also tended to be in agreement with the original acceptance testing measurements and results from similar facilities published in the literature. Simulations illustrated that most of the neutrons entering the patient are produced in the final patient-specific aperture and precollimator just upstream of the aperture, not in the scattering system. These new results confirm that the dose equivalents received by patients outside the primary proton field from primary particles that leak through the nozzle are below the accepted standards for x-ray and electron beams. The total dose equivalent outside of the field is similar to that received by patients undergoing treatments with intensity modulated x-ray therapy. At the center of a patient for a whole course of treatment, the dose equivalent is comparable to that delivered by a single whole-body XCT scan.

The experiment 'Dosimetric Mapping' conducted as part of the science program of NASA's Human Research Facility (HRF) between March and August 2001 was designed to measure integrated total absorbed doses (ionising radiation and neutrons), heavy ion fluxes and its energy, mass and linear energy transfer (LET) spectra, time-dependent count rates of charged particles and their corresponding dose rates at different locations inside the US Lab at the International Space Station. Owing to the variety of particles and energies, a dosimetry package consisting of thermoluminescence dosemeter (TLD) chips and nuclear track detectors with and without converters (NTDPs), a silicon dosimetry telescope (DOSTEL), four mobile silicon detector units (MDUs) and a TLD reader unit (PILLE) with 12 TLD bulbs as dosemeters was used. Dose rates of the ionising part of the radiation field measured with TLD bulbs applying the PILLE readout system at different locations varied between 153 and 231 microGy d(-1). The dose rate received by the active devices fits excellent to the TLD measurements and is significantly lower compared with measurements for the Shuttle (STS) to MIR missions. The comparison of the absorbed doses from passive and active devices showed an agreement within +/- 10%. The DOSTEL measurements in the HRF location yielded a mean dose equivalent rate of 535 microSv d(-1). DOSTEL measurements were also obtained during the Solar Particle Event on 15 April 2001.