Rapid Lymphatic Clearance After Subcutaneous Extravasation of 177 Lu-PSMA-I&T Radioligand Therapy.

Extravasation of therapeutic radiopharmaceuticals during radioligand therapy is uncommon. We report the first published case of subcutaneous extravasation of 177 Lu-PSMA-I&T, presenting with acute upper-arm swelling, pain, and transient autonomic symptoms. Early planar scintigraphy and SPECT/CT demonstrated intense radiotracer accumulation in the left upper arm, with rapid redistribution and near-complete clearance by 20 hours. Dosimetric analysis estimated an absorbed dose of ~8 Gy at the injection site. Conservative management resulted in no radiation-induced tissue injury. The clinical course was comparable to previously reported cases of 177 Lu-PSMA-617 extravasation. This case highlights the value of early imaging in the case of extravasation for evaluating the extent of the extravasation and enabling absorbed dose estimation.