Case Report of a Clinically Significant Lu-177 Extravasation: Rapid Clearance Kinetics and Dosimetry Using Quantitative SPECT/CT
Abstract
Purpose
Extravasation during radiopharmaceutical therapy can retain a substantial fraction of administered activity at the injection site, creating high local absorbed doses and potential tissue injury while reducing delivery to target tumors. For Lu-177 therapies, timely quantitative assessment of infiltrated activity, clearance, and extravasation dosimetry is essential for patient management.
Methods
A patient receiving Lu-177 DOTATATE (Lutathera, 200 mCi) was identified with an extravasation early during administration; the infusion was stopped and IV access re-established. Local hyperthermia and arm elevation were used to promote clearance. Post-administration, infiltrated activity was quantified using (1) a hand-held CZT detector (RAVIN CAM) and (2) an xSPECT Quant protocol on a NaI SPECT/CT system. The first SPECT/CT defined the extravasated volume (VOI = 1070 mL) and activity, a second SPECT/CT 4.57 h later enabled effective half-life (Teff) estimation and patient-specific dosimetry with MIRDcalc (sphere model).
Results
Quantitative SPECT/CT estimated 66.6 mCi, while the external detector estimated 61.8 mCi (7% difference). SPECT/CT data showed a decrease from 66.6 mCi to 28.0 mCi over 4.57 h, yielding Teff = 3.66 h, consistent with rapid clearance. The mean absorbed dose to the 1070 mL infiltrated soft-tissue compartment was 1.035 Gy (self-dose only). Two low-dose CTs used for localization and attenuation correction had CTDIvol of 5.37 mGy each, corresponding to a total effective dose of 15 mSv calculated with MIRDct. The measured short Teff did not require more restrictive patient release criteria than the default 56.1 h value.
Conclusion
This case demonstrates a practical Lu-177 extravasation workflow: rapid identification with an external detector, quantitative SPECT/CT activity estimation, and a second time point for Teff-based dosimetry. Despite one-third of the planned activity infiltrating, rapid clearance limited the mean compartment dose to ~1 Gy, and patient release guidance remained within standard practice while incurring a low additional CT dose.