External radiation exposures from lutetium-177 DOTATATE therapy patients.

Objectives To estimate the patient self-attenuated exposure rate constant and external total body doses to personnel from a ¹⁷⁷Lu DOTATATE (Advanced Accelerator Applications) therapy patient.

Methods Exposure rates (mR/h) at 1 m from 20 therapy administrations (200 mCi), were measured at the level of the upper abdomen (A) and bladder (B), with a calibrated ion chamber survey meter (451B, Fluke Biomedical) three times; at the end of the ½-h infusion, after the first urination and at the time of release. Release was based upon ¼ of the standard limits, to account for the four fractions of treatment and recurring doses to others. The higher of the initial A and B mR/h was used to compute the self-attenuated exposure rate constant (E, mR-m²/mCi-h). Cumulative whole body doses (μSv) to the NM (NMT) and electrocardiograph (EKGT) technologists and nurse (N) caring for the patient during each 4-h infusion and uptake period, were measured with electronic personal dosimeters (RAD-60, Mirion Technologies).

Results The mean±σ (range) administered mCi was 204±8 (181-214). The calculated E was 0.0115±0.0018 (0.0091-0.0160); and it correlated significantly with body suface area, but with a small slope (y=-0.0035x+0.0177, r=0.44). The doses to personnel from each treatment (μSv) were NMT: 18.8±7.2 (8-34); N: 16.0±7.3 (3-31); and EKGT: 5.9±3.7 (2-14). The EKGT dose was significantly lower than that of both the NMT and N (p<<0.05, one-tailed t-Test).

Conclusions The average measured E was 63% of the in-air value. All patients were releasable at 4-h based on measured E and effective halflife (56 h), while keeping the dose to the most-exposed-person below 1.25 mSv and that to children and pregnant women below 0.25 mSv. The NMT, N and EKGT per treatment personnel doses were 2.44, 2.08 and 0.77 times our NMTs' daily dose (7.7±2.2 μSv, averaged over one year).