58 Dose estimation for an extravasation in a patient treated with 177Lu-DOTATATE

Introduction Extravasation of radiopharmaceuticals used for therapy purpose, such as Lu-177 ( E β Max = 498 keV, E γ = 113 keV (6%) and 208 keV (10%), T  = 6.6 days) can lead to severe tissue damage [1] . In September 2017, an extravasation occurred in the arm of a patient during a 7.4 GBq perfusion of lutathera ® (AAA). Methods Four whole body (WB) acquisitions were performed at 2 h, 5 h, 20 h and 26 h after the beginning of the perfusion (H0). Three SPECT/CT were performed following the WB acquisitions at 5 h, 20 h and 26 h. Images were acquired with a Symbia T2® camera (Siemens Healthcare) with a MELP collimator, a main window around 208 keV, 20 cm/min for the WB acquisition and 2x30 projections of 30s for the SPECT acquisition. A local quantification procedure developed for renal dosimetry and based on a calibration factor was used, with the following parameters: FLASH 3D®, 10 iterations, 10 subsets, CT-based attenuation correction, scatter correction and 4 mm FWHM Gaussian filtering. Effective period was determined on the geometric mean of whole body images. Given the complexity of subcutaneous tissue contouring, 3 volumes (V1  = 180, V2  = 400 et V3  = 1000 mL) were defined on SPECT images using a 3D threshold. Cumulated activities and associated doses (D1, D2, D3) were calculated in the 3 volumes using a conversion factor ξ = 0.0024 mGy.g/(MBq.s), from the website RADAR [2] . Results Estimated effective periods were 11 h in the whole body and 3 h in the arm. As SPECT images at H0  + 2 h were not available, activity at H0  + 2 h was evaluated using estimated activity from SPECT images at H0  + 5 h and a ratio of the number of counts in a ROI around the arm on geometric mean of WB images at H0  + 2 h and at H0  + 5 h. Cumulated activities were evaluated using a mono exponential fit on activities calculated on SPECT images. Estimated doses in V1, V2 and V3 were D1  = 7.8 Gy, D2  = 5.4 Gy and D3  = 2.8 Gy. Conclusions Estimated doses values are in the range of deterministic effects. However, the patient did not show any clinical sign of the irradiation. Elimination of the product was quick in the arm (Teff  = 3 h) and was promoted by specific interventions (warming, repeated massages around the injection site).