Radiation emission dose from patients administered Y-90-labelled radiopharmaceuticals: comparison of experimental measurements versus Monte Carlo simulation

Aim To estimate the radiation dose delivered from patients injected with yttrium-90 (Y-90)-labelled tiuxetan (Zevalin) to parents and the general population, comparing different techniques. Methods The radiation dose delivered from a group of eight patients injected with Y-90-Zevalin to treat recurrent lymphoma was measured. The data obtained with the Monte Carlo simulation test were compared with the experimental measurements obtained with an ionization chamber detector and with a crystal Nal(TI) detector. Results A good correlation was found between the Monte Carlo simulation test and the ionization chamber detector results: the air kerma dose rate was 4.2 +/- 0.1 and 4.4 +/- 0.8 mu Gy/h, respectively (r = 0.9, P < 0.01). Moreover, more than 99.7% of the air kerma dose rate measured with the ionization chamber detector was because of the contribution of electrons, whereas the contribution of photons was less than 0.3%. In contrast, the air kerma dose rate measured with the crystal Nal(TI) detector was significantly lower (0.76+0.12 mu Gy/h) in comparison wit the Monte Carlo simulation test. This underestimation was related to the limited crystal Nal(TI) detector response to low energy rates at variance with the ionization chamber detector. The effective radiation dose released by patients treated with Y-90-labelled tiuxetan to parents and the general population was approximately 0.1 mSv per treatment cycle. Conclusion Using the Monte Carlo model as a benchmark to compare the experimental measurements obtained by the two different detectors, we found that the ionizing chamber detector was more accurate than the crystal Na(TI) detector for measuring the exposure radiation dose delivered from patients administered with Y-90-labelled radiopharmaceuticals. Moreover, the effective radiation dose released by these patients to their parents and the general population is significantly lower than the value recommended by international reports and regulations.