[en] Full text: Radiation exposure of other persons from patients to whom radioactive materials have been administered is often a concern in nuclear medicine. This is particularly so in cases where patients are returning to young families after administration of relatively large activities of ¹³¹l iodide for therapeutic purposes; also, on occasion, some diagnostic radiopharmaceuticals (e.g. ¹¹¹ln leucocytes in activities exceeding 30 MBq) may also result in significant external exposures. Total radiation exposure depends critically on the clearance rate of the radioactive material from the body (effective half-life), external exposure rate per unit activity, the amount of radioactive material administered and the close contact exposure pattern. In order to limit the exposure to acceptable levels, it may be necessary to alter or restrict exposure patterns and/or avoid close contact altogether for a designated time after administration of the radioactive material. Spreadsheet templates which automatically calculate cumulative exposures from patients based on any single, bi- or tri-exponential whole body clearance rate and any diurnal (or any other periodic) exposure pattern have been developed at by the authors. The method used is an adaptation of that originally described by Mountford et al. The time (post-administration) during which contact should be avoided in order to constrain the radiation exposure to a selected maximum is also calculated using an iterative technique (Newton's method). These templates find particular application in the calculation of exposures to persons who are in contact with patients who have received ¹³¹l iodide for therapeutic purposes. In thyrotoxic patients for example, using typical retention data, avoidance of close contact with very young children is indicated for 25 days post administration if radiation exposure is to be limited to 1 mGy, and 10 days if radiation exposure is to be limited to 5 mGy (assuming an administered activity of 555 MBq). The effect of changing dose limits, exposure patterns and using individually derived clearance rates may be readily modelled using the spreadsheet templates