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

Abstract

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 (pvalue ≥ 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.