Resumen
Background: As for any other nuclear medicine treatment, patients treated
with [177
Lu]Lu-DOTA-TATE should be given some radiation protection recommenda-
tions 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 restric-
tion periods based on measurements taken before discharge.
Methods: 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 T 6,24
eff was calculated from a mono-exponential fit per-
formed with the 6 h and 24 h measurements and compared with the effective decay
time T 24,48,168
eff 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 T 6,24
eff .
A modified effective decay T 6,24
eff, mod was obtained by adding the correction factor
to T 6,24
eff 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.
Results: 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 recom-
mendations on radiation protection determined from the first cycle could reasonably
be used for the remaining cycles in most patients. The values of T 6,24
eff and T 24,48,168
eff
obtained for the 20 patients were significantly different. The 95th percentile of the dif-
ferences between T 6,24
eff and T 24,48,168
eff was 46 h, which is thus the time to be added
to T 6,24
eff so as to determine the restriction periods.