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Besides the effects of the microgravity environment, and the psychological and psychosocial problems encountered in confined spaces, radiation is the main health detriment for long duration human space missions. The radiation environment encountered in space differs in nature from that on earth, consisting mostly of high energetic ions from protons up to iron, resulting in radiation levels far exceeding the ones encountered on earth for occupational radiation workers. Therefore the determination and the control of the radiation load on astronauts is a moral obligation of the space faring nations. The requirements for radiation detectors in space are very different to that on earth. Limitations in mass, power consumption and the complex nature of the space radiation environment define and limit the overall construction of radiation detectors. Radiation dosimetry onboard the International Space Station (ISS) is onboard the International Space Station (ISS) is accomplished to one part as "operational" dosimetry accomplished to one part as "operational" dosimetry aiming for area monitoring of the radiation environment as well as astronaut surveillance. Another part focuses on "scientific" dosimetry aiming for a better understanding of the radiation environment and its constitutes. Various research activities for a more detailed quantification of the radiation environment as well as its distribution in and outside the space station have been accomplished in the last years onboard the ISS. The paper will focus on the current radiation detectors onboard the ISS, their results, as well as on future planned activities.

The EROPAQ project for TLD monitoring of photon beams started in June 1994 with the set-up of the TLD system: calibration, reading and evaluation procedures. The acceptance level of +/- 3% was set for the TLD intercomparisons. The policy of the project was to check all beams in 47 participating radiotherapy centres and to recheck all the beams in those centres, where a deviation exceeding +/- 3% occurred in one or more of the beams. Out of 129 beams checked, 100 beams (78%) were found within the +/- 3% limit. Eleven beams show deviations larger than +/- 6%, and immediate corrective action was undertaken. Out of 47 centres checked, 22 did not participate in any external audit in a preceding 5 years. In these centres 68% (34/50) of the total number of gamma and x-ray beams checked but only 59% (20/34) of gamma beams were within the acceptance level, while in the 25 centres, which participated in an external audit before, these figures were 84% (66/79) and 88% (35/40) respectively. The sources of discrepancies were thoroughly investigated, discussed with the participants and the errors corrected. Poor results were in several cases associated with very old design of radiotherapy units and old dosimetry systems, equipped with inadequate ionization chambers. In several centres, an insufficient training of the physicists in clinical dosimetry was observed. Thanks to the corrective action, a great improvement of calibration of the beams was achieved. Standard deviation of the distribution of the results for all x and gamma beams checked decreased from SD = 7.4% at the first check to SD = 2.5% at the second check.

The recent international standards published by the International Electrotechnical Commission (IEC) on the performance of medical electron accelerators describe suggested test procedures for the performance of radiotherapy accelerators. The recommendations of the Nordic Association of Clinical Physics for testing of the radiation beam characteristics include test conditions, methods and suggested tolerances that are different from those of the IEC. In this work the two publications were compared for acceptance testing of a Philips SL25 linear accelerator. It is important to gain experience on the practical use of these standards.

In 1987 mechanical checks of megavoltage units and simulators were included in the on-site physics program of the EORTC. The results reported were obtained in 16 different centres and concern 23 accelerators, 14 cobalt units and 14 simulators. In general, the deviations observed for accelerators and simulators are smaller than for cobalt units. A single score, based on the deviations observed for the mechanical checks, is attributed to each centre.