The Interference of Gamma Rays With Bone Mineral Density Measurements in ¹⁷⁷Lu-PSMA and DOTATATE Therapy

The main purpose was to describe the interference of gamma radiation emitted by ¹⁷⁷Lu with simultaneous bone mineral density BMD measures for patients undergoing ¹⁷⁷Lu-PSMA and ¹⁷⁷Lu DOTATATE therapy. A cohort of 9 patients underwent ¹⁷⁷Lu-PSMA therapy were randomly selected to speculate the activity in the abdominopelvic region. So that, SPECT/CT scan at 24 h was used with attenuation and scatter correction. The activities were derived from the delineated ROIs over the abdominopelvic zone showing a range of 34-274 MBq. Next, a water path was placed under spine phantom mimicking L1-L4 vertebrae and followed by consecutive DEXA scans made by Hologic 4500 W and GE-Lunar DPX-NT systems. Five scans were performed without/and with different Lu-177 activities 37, 185, 370 and 555 MBq under the same geometric conditions. The obtained BMD readings of L1-L4 by the Hologic device were 1.027, 1.024, 1.021, 1.013, and 1.006 g/cm² with presence of 0, 37, 185, 370, and 555 MBq ¹⁷⁷Lu activity, respectively. Whereas, in Lunar device, it was found as higher as 1.163, 1.121, 1.09, 1.072, and 1.043, respectively. There was no statistically significant difference between both devices (p_value ≥ 0.05). The fluctuation ranges in the L1-L4 BMD readings at the presence of 37-555 MBq were 0.3%-2%, and 3.6%-10.3% for Hologic and Lunar systems, respectively. It was emphasized that gamma radiation emitted by ¹⁷⁷Lu relatively influence DEXA scans and the yielded BMD measures. Postponing DEXA scans as early as 8 d after ¹⁷⁷Lu-PMSA and 11 d after ¹⁷⁷Lu-DOTATATE therapies is recommended to avoid the erroneous contribution of gamma radiation and provide precise bone assessment.