Tissue dose estimation after extravasation of Lu-DOTATATE.

Background: Extravasation of radiopharmaceuticals used for vectorized internal radiotherapy can lead to severe tissue damage (van der Pol et al., Eur J Nucl Med Mol Imaging 44:1234-1243, 2017). Clinical management of these extravasations requires the preliminary estimation of the dose distribution in the extravasation area. Data are scarce regarding the dose estimation in the literature. This work presents a methodology for estimating the dose distribution after an extravasation occurred in September 2017, in the arm of a patient during a 7.4-GBq infusion of Lutathera ® (AAA).

Methods: A local quantification procedure initially developed for renal dosimetry was used. A calibration factor was determined and verified by phantom study. Extravasation volume of interest and its variation in time were determined using 4 whole body (WB) planar acquisitions performed at 2 h (T), 5 h (T), 20 h (T), and 26 h (T) after the beginning of the infusion and three SPECT/CT thoracic acquisitions at T, T, and T. For better estimation of initial extravasation volume, 3 volumes were defined on SPECT images using a 3D activity threshold. Cumulated activities and associated absorbed doses (D, D, D) were calculated in the 3 volumes using the MIRD formalism.

Results: Volumes estimated using 3D threshold were V = 1000 mL, V =400 mL, and V =180 mL. Cumulated activities were evaluated using a monoexponential fit on activities calculated on SPECT images. Estimated local absorbed doses in V, V, and V were D = 2.3 Gy, D = 4.1 Gy, and D = 6.8 Gy. Evolution in time of local activity in the extravasation area was consistent with an effective local half-life (T) of 2.3 h.

Conclusions: Rapid local dose estimation was permitted thanks to knowledge of the calibration factor determined previous to accidental extravasation. Lutathera® lymphatic drainage was quick in the arm (T = 2.3h). Estimated doses were in the lower range of deterministic effects and far under soft tissue necrosis threshold. Thus, no surgical rinse was proposed. The patient did not show any clinical consequence of the extravasation.