101. Tandem high-dose 131I-mIBG therapy in paediatrics: Dosimetry-based treatment and radiation exposure monitoring of family caregivers

Purpose Tandem high-dose based on two administrations of 131I-meta iodobenzylguanidine (131I-mIBG) is the treatment of choice for children with neuroblastoma (NB) with the aim to improve palliation and progression-free survival rates, especially in patients who have undergone a large amount of prior chemotherapy treatments. The present study aims to report the results of in vivo patient’s dosimetry as well as of radiation exposure to family caregivers. Methods Five children with relapsed/refractory NB were treated with 131I-mIBG between 2016 and 2017. Absorbed doses to whole body (WB) and red marrow (RM) were calculated according to MIRD and EANM guidelines. The calculation of WB absorbed dose for the first administration was used to determine the second activity to be administered to reach a total WB absorbed dose of 4 Gy. During patient’s isolation and the following hospitalization, the family members received an electronic personal dosimeter for monitoring their exposure. Results A dosimetry-based high-dose 131I-mIBG therapy of children with NB has been successfully established and routinely performed in our institution. The injected activity by administration was from 6610 to 10870 MBq (median: 8491 MBq), resulting in WB doses ranging from 0.79 to 2.40 Gy (median: 1.38 Gy) and in RM doses from 0.59 to 2.44 Gy (median: 0.88 Gy). Radiation dose to family caregivers ( H p [10]) varied from 0.4 to 16.6 mSv, with a mean WB exposure of 0.4 μSv/MBq. Conclusions For treatment of neuroblastoma, the WB absorbed doses could be prescribed individually in order to perform an adequate treatment and avoid hematologic toxicity. This is especially true in paediatrics where a highly heterogeneous and heavily pretreated patient population has to be treated. Radiation doses to family caregivers should be accurately evaluated considering the effective dose values established by the European Union regulation.