Person volunteered with full informed consent as a subject of biomedical research, e.g. causing radiation exposure of the subject. He/she may get or may not get a direct medical benefit from the study. The research programme should subject to, according to national regulations if relevant, approval from an appropriate review committee like an 'Ethic Committee'. Radiation exposure of the volunteer is regarded as a special case of medical exposure and, therefore, the individual dose limits do not apply. The regulatory body or the review committee, however, may impose a dose constraint proportionating the value of the research programme.
ICRP Glossary entry - June 2019