| Popis: |
Background. Extravasation of radiopharmaceuticals used for vectorized internal radiotherapy can lead to severe tissue damage (1). 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 2h (T2h), 5h (T5h), 20h (T20h) and 26h (T26h) after the beginning of the infusion and three SPECT/CT thoracic acquisitions at T5h, T20h and T26h. 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 (D1, D2, D3) were calculated in the 3 volumes using the MIRD formalism.Results. Volumes estimated using 3D threshold were V1= 1000 mL, V2=400 mL and V3=180 mL. Cumulated activities were evaluated using a mono exponential fit on activities calculated on SPECT images. Estimated local absorbed doses in V1, V2 and V3 were D1 = 2.8 Gy, D2 = 5.4 Gy and D3 = 7.8 Gy. Evolution in time of local activity in the extravasation area was consistent with an effective local period (Teff) of 3 hours.Conclusions. Rapid local doses estimation was permitted thank to knowledge of the calibration factor determined previous to accidental extravasation. Luthatera® lymphatic drainage was quick in the arm (Teff = 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 theses extravasation. |
