Personalized dosimetry for a deeper understanding of metastatic response to high activity 131 I-mIBG therapy in high risk relapsed refractory neuroblastoma.

Background: Dosimetry in molecular radiotherapy for personalized treatment is assuming a central role in clinical management of aggressive/relapsed tumors. Relapsed/refractory metastatic high-risk neuroblastoma (rrmHR-NBL) has a poor prognosis and high-activity ¹³¹ I-mIBG therapy could represent a promising strategy. The primary aim of this case series study was to report the absorbed doses to whole-body ( D _WB ), red marrow ( D _RM ) and lesions ( D _Lesion ). A secondary aim was to correlate D _Lesion values to clinical outcome.
Methods: Fourteen patients affected by rrmHR-NBL were treated with high-activity ¹³¹ I-mIBG therapy (two administrations separated by 15 days). The first administration was weight-based whereas the second one was dosimetry-based (achieving D _WB equals to 4 Gy). In all patients D _WB and D _RM was assessed; 9/14 patients were selected for D _Lesion evaluation using planar dosimetric approach (13 lesions evaluated). Treatment response was classified as progressive and stable disease (PD and SD), partial and complete response (PR and CR) according to the International Neuroblastoma Response Criteria. Patients were divided into two groups: Responder (CR, PR, SD) and Non-Responder (PD), correlating treatment response to D _Lesion value.
Results: The cumulative D _WB , D _RM and D _Lesion ranged from (1.5; 4.5), (1.0; 2.6) and (44.2; 585.8) Gy. A linear correlation between D _WB and D _RM and a power law correlation between the absorbed dose to WB normalized for administered activity and the mass of the patient were observed. After treatment 3, 2, 4 and 5 patients showed CR, PR, SD and PD respectively, showing a correlation between D _Lesion and the two response group.
Conclusions: Our experience demonstrated feasibility of high activity therapy of ¹³¹ I-mIBG in rrmHR-NBL children as two administration intensive strategy. Dosimetric approach allowed a tailored high dose treatment maximizing the benefits of radionuclide therapy for pediatric patients while maintaining a safety profile. The assesment of D _Lesion contributed to have a deeper understaning of metabolic treatment effects.
Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://dx.doi.org/10.21037/qims-21-548). The authors have no conflicts of interest to declare
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