The Institute of Physics & Engineering in Medicine, Practical Aspects of Personal Dosimetry, Manchester Royal Infirmary, 1 May 1997

Abstract

The meeting was organised by the IPEM Radiation Protection Special Interest Group. The morning session included talks on the practical aspects of routine personal dosimetry. New methods of assessing radiation dose such as prototype GEMS, optically stimulated luminescence and TLD 100H high sensitivity lithium fluoride were discussed in the afternoon. The meeting was opened with a presentation on the importance of syringe shields in diagnostic nuclear medicine, where surface doses can be as high as 15 mSv min-1, and the effect of the new ICRP 60 recommendations on Nuclear Medicine Departments. ICRP 60 recommends that finger doses are assessed by averaging over 1 cm2 rather than 100 cm2, consequently finger dose assessments will have to be undertaken using finger stall devices rather than ring or hand monitors currently in use at some hospitals. ICRP 60 also recommended that pregnant workers are limited to receiving 1 mSv during the declared term of pregnancy. This may result in limiting the number of injections containing radioactive material pregnant workers are allowed to administer. The session continued with a discussion on the practical aspects of internal dosimetry. As only a small number of personnel working for the NHS are classified radiation workers for internal doses, the facilities available for internal dose assessment within the NHS are limited. The various monitoring techniques used and associated uncertainties were reviewed. The effect that changes to annual limits of intake and mathematical models have on effective dose assessments were discussed in detail, the most dramatic being the effective dose resulting from the inhalation of 232Th being reduced by a factor of 20. The average occupational radiation exposure in Diagnostic Radiology Departments was reviewed by Mr D Rawlings from Newcastle General Hospital. Generally, radiation doses are low, with less than 2% of the people monitored receiving over 1 mSv. He concluded that the radiation dose received by personnel was dependent on the type of procedure, duties undertaken and the skill and experience of the staff. New radiological techniques and/or changes in equipment may also have an increased potential for occupational exposure. The equipment and methods used to monitor individual radon dosimetry was discussed by Mr Shaw from the NRPB. Passive, active and air sampling were all discussed in detail together with the associated problems and inaccuracies. Mr Shaw emphasised the requirement for employers to be aware that radon risk assessments were required in radon affected areas. The final session of the morning was an interesting talk on personal exposure to solar ultraviolet (UVR) by Professor B L Diffey of the Regional Medical Physics Department in Durham. The main conclusions of a large study of personal UVR exposure recently conducted were that there is no variation in the UVR exposure between sexes and young children receive a greater UVR dose than adolescents. The talk concluded with a discussion on the effectiveness of well known methods of reducing UV exposure and one surprising fact: people who use sun protectors are more likely to develop melanoma than people who do not use sun protectors. Mr Shaw opened the afternoon session by explaining in simplistic terms the more confusing aspects of the new dose reporting quantities. The talk concentrated on neutron doses, where in some instances the effective dose could be up to a factor of 4 higher than the effective dose equivalent. The speaker also highlighted the need for low dose measurements and the requirement of dosimetry services to reduce the limit of detection of dosemeters to a maximum of 0.15 mSv. Mr D S Arnold from RRPPS talked about the practical aspects of calibrating personal dosemeters followed by a short presentation on Gamma Extremity Monitoring System (GEMS). GEMS is designed to provide a continuous readout of dose-rate from a small CdTe probe attached to the finger. The advantages (rapid access to dose results, real time counting and simplicity) and disadvantages (energy dependence and non-linearity) were highlighted. The final presentations of the meeting covered three new types of dosimetry. The characteristics of optically stimulated luminescence: extremely stable; sensitivity 50 times greater than TLD 100 and partial processing allowing re-read at a later date were outlined by Dr Finnigan from Landauer Inc. The technical specification of the Siemens EPD2 Electronic Personal Dosemeter was discussed by Mr K Lakin from Vertec Scientific Limited who emphasised the benefit of using this type of dosemeter in a hospital environment. Finally, Mr S Evans from Derbyshire Royal Infirmary presented experimental data on the new high sensitivity TLD 100H lithium fluoride. The high sensitivity, low limit of detection, flat energy response and potential small size of dosemeters possible suggests the material is ideal for use in personal dosemeters. However, the 15% variation in sensitivity after a number of calibrations was cause for concern and continued experimentation was recommended before the department would consider changing from TLD 100.