  Objective. Patients treated with radionuclide therapy may require
restrictions on certain activities for a period of time following treatment to
optimise protection of the public and ensure the legal dose limit is not
exceeded. Software may be used to calculate necessary restriction periods for
an individual based on longitudinal dose rate measurements from the time of
radiopharmaceutical administration. A spreadsheet program has been used for
this purpose in Australian hospitals for the last two decades. However, this
spreadsheet has a limitation in that it uses an approximation in the
calculation of dose from a contact pattern, which affects the calculated
restriction period. A computer program called Dorn was developed that provides
the same functionality as the spreadsheet but without this approximation.
Proffered radiation safety advice from Dorn and the spreadsheet were compared.
Approach. Advice from the spreadsheet and Dorn were compared for 55 patients
who underwent iodine-131 therapy for differentiated thyroid cancer. Main
results. The restriction periods for caring for infants, close contact with
children and sleeping with a partner were typically about 13 hours longer in
Dorn than in the spreadsheet, but in some cases were over a week shorter or a
month longer. Significance. If the Dorn program is used clinically in place of
the spreadsheet, some patients will enjoy shorter restriction periods and the
therapy provider can be more confident in their compliance with regulatory
requirements and best practice. Dorn is freely available from
https://doi.org/jg5f.
