Individualisation of radiation protection recommendations for patients treated with [¹⁷⁷Lu]Lu-DOTA-TATE

As for any other nuclear medicine treatment, patients treated with [¹⁷⁷Lu]Lu-DOTA-TATE should be given some radiation protection recommendations after being discharged to limit the dose received by family members and public. The restriction periods will depend on the remaining activity at the time of discharge, the washout rate and patients' personal conditions. The activity in patients' whole-body follows a bi-exponential behaviour. At the time of discharge only the first part of the time-activity curve is known. However, the second phase of the bi-exponential curve should be known to individualize the time of restrictions. The main purpose of this prospective study was to establish a simple method for calculating the restriction periods based on measurements taken before discharge.

The whole-body time-activity curve was calculated for 20 patients from dose-rate measurements performed during the first week post-administration. An effective decay time [Formula: see text] was calculated from a mono-exponential fit performed with the 6 h and 24 h measurements and compared with the effective decay time [Formula: see text] obtained from the mono-exponential fit performed with the 24 h, 48 h and 168 h measurements. The differences between them were calculated and the 95th percentile of these differences was used as a correction factor for [Formula: see text]. A modified effective decay [Formula: see text] was obtained by adding the correction factor to [Formula: see text] and the restriction periods for each patient was calculated. The whole body activity washout between the first and the fourth treatment cycles of 16 patients was also compared.

The comparison of the whole-body activity curves between the first and the fourth cycle of the treatment for 16 patients would indicate that the recommendations on radiation protection determined from the first cycle could reasonably be used for the remaining cycles in most patients. The values of [Formula: see text] and [Formula: see text] obtained for the 20 patients were significantly different. The 95th percentile of the differences between [Formula: see text] and [Formula: see text] was 46 h, which is thus the time to be added to [Formula: see text] so as to determine the restriction periods.

The proposed method makes it possible to calculate the restriction periods for patients treated with [¹⁷⁷Lu]Lu-DOTA-TATE before they leave the hospital in a conservative and individualized way.