An analysis of personnel dose records which justifies the application of cost-benefit analysis techniques in the design of an afterloading facility and the use of controlled areas and systems of work within suite to control occupational exposure. 
The sealed source operational policies employed at the Bristol Radiotherapy and Oncology Centre were originally designed to meet the requirements of the 1972 Code of Practice by ensuring that individual personnel doses were kept below the relevant quarterly and annual dose limits.  In 1982-1983, measures were taken to improve personnel radiation safety within the brachytherapy treatment facility by (a) making preparations for the introduction of Selectron medium-dose-rate (MDR) afterloading systems at the centre for intracavitary brachytherapy and (b) reviewing the operational policies to ensure that they meet the more stringent requirements of the ALARA (as low as reasonably achievable) principle, a principle subsequently embodied in the 1985 UK ionising Radiations Regulations (IRR 85).  When considering the implications of making existing single-bedded side wards, originally designed for low-dose-rate brachytherapy and suitable for the new systems, the cost of the extra protection required to reduce the instantaneous dose rate in the ward corridors adjacent to the treatment room to less than 7.5 microSv h-1 had to be determined.  On the basis of the cost-benefit analysis, it was decided not to provide additional shielding but rather to introduce administrative controls based on local rules which contained systems of work and the operational policies for the afterloading systems.  After using the MDR afterloading systems for 2 years, a period in which there has also been a marked increase in interstitial brachytherapy, an analysis was made of the doses received by nursing staff over the past 8 years.  This has shown that, in spite of higher dose rates in the corridor areas because of the use of an MDR system and the increase in interstitial techniques, the doses to ward nurses have been significantly reduced by encouraging staff to comply with the ALARA principle and the introduction of afterloading systems.