LAUSR

Introduction The calculation of resin yttrium-90 (90Y-) microspheres activity for selective internal radiotherapy (SIRT) needs to be investigated. Methods and materials Analyses using Simplicit90Y (Boston Scientific, Natick, Massachusetts, USA) dosimetry software were performed to determine the concordance between the absorbed doses to the tumor (DT1 and DT2) and healthy liver (DN1 and DN2) during the pre-treatment and the post-treatment phases. An optimized calculation of the activity of 90Y-microspheres performed using dosimetry software was applied retrospectively to assess the impact of this calculation method on the treatment. Results DT1 ranged from 38.8 to 372 Gy, with a mean value of 128.9 ± 73.6 Gy and median of 121.2 Gy [interquartile range (IQR): 81.7–158.8 Gy]. The median DN1 and DN2 was 10.5 Gy (IQR: 5.8–17.6). A significant correlation was between DT1 and DT2 (r = 0.88, P < 0.001) and DN1 and DN2 (r = 0.96, P < 0.001). The optimized activities were calculated; the target dose to the tumor compartment was 120 Gy. No activity reduction was applied in accordance with the tolerance of the healthy liver. Optimization of the microspheres dosages would have resulted in a significant increase in activity for nine treatments (0.21–2.54 GBq) and a reduction for seven others (0.25–0.76 GBq). Conclusions The development of customized dosimetry software adapted to clinical practice makes it possible to use dosimetry to optimize the dosage for each patient.