Radiation exposure after permanent prostate brachytherapy

Abstract

Background and purpose: Limited information is available on the true radiation exposure and associated risks for the relatives of the patients submitted to prostate brachytherapy with permanent implant of radioactive sources and for any other people coming into contact with them. In order to provide appropriate information, we analyzed the radiation exposure data from 216 prostate cancer patients who underwent (125)I or (103)Pd implants at the European Institute of Oncology of Milan, Italy.

Patients and methods: Between October 1999 and October 2004, 216 patients with low risk prostate carcinoma were treated with (125)I (200 patients) or (103)Pd (16 patients) permanent seed implantation. One day after the procedure, radiation exposure measurements around the patients were performed using an ionization chamber survey meter (Victoreen RPO-50) calibrated in dose rate at an accredited calibration center (calibration Centre SIT 104).

Results: The mean dose rate at the posterior skin surface (gluteal region) following (125)I implants was 41.3 microSv/h (range: 6.2-99.4 microSv/h) and following (103)Pd implants was 18.9 microSv/h (range 5.0-37.3 microSv/h). The dose rate at 50 cm from the skin decreased to the mean value of 6.4 microSv/h for the (125)I implants and to the mean value of 1.7 microSv/h for the (103)Pd implants. Total times required to reach the annual dose limit (1 mSv/year) recommended for the general population by the European Directive 96/29/Euratom and by the Italian law (Decreto Legislativo 241/2000) at a distance of 50 cm from the posterior skin surface of the implanted patient would be 7.7 and 21.6 days for (125)I and for (103)Pd. Good correlation between the measured dose rates and both the total implanted activity and the distance between the most posteriorly implanted seed and the skin surface of the patients was found.

Conclusions: Our data show that the dose rates at 50 cm away from the prostate brachytherapy patients are very low and that the doses possibly absorbed by the relatives and other members of the general population coming into contact with the treated patients are well below the dose limit set by the European Directive and by the Italian regulation. However, in order to meet the recommendation of the ALARA principle (As Low As Reasonably/Readily Achievable), some advice to the patients should be given, such as to maintain a minimum distance from the patient of 1m, at least for a period equal to one half life of used radionuclide (60 days for (125)I and 15 days for (103)Pd).