O Kwon*, J Grudzinski, D Adam, P Clark, R Sriramaneni, C Ferreira, J Jeffery, C Massey, C Kerr, Z Morris, R Hernandez, J Weichert, B Bednarz, University of Wisconsin-Madison, Madison, WI

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  O Kwon

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SU-E-202-6 (Sunday, 7/10/2022) 1:00 PM - 2:00 PM [Eastern Time (GMT-4)]

Room 202

Purpose: The accurate estimation of absorbed doses to normal organs and tumors is important for establishing dose-response relationships in radiopharmaceutical therapy (RPT). In this regard, RAPID (Radiopharmaceutical Assessment Platform for Internal Dosimetry), a subject-specific Monte Carlo internal dosimetry platform, has been developed and utilized for various purposes in preclinical and clinical research. Here, RAPID was expanded to utilize high-resolution micro-SPECT/CT images to perform dosimetry in mice with intracranial brain tumors treated with RPT.

Methods: Two C57BL/6 mice with GL261 gliomas injected with approximately 500 μCi of 177Lu-NM600 were scanned using micro-SPECT/CT at 7-, 29-, 52-, and 77-hours post-injection and monitored using both T1-Gd and T2 MRI. ROIs of the normal brain, brain tumors, and right flank tumors were drawn using both CT and MRI, and mean percent injected dose in each ROI was determined as a function of time. RAPID in vivo concentration and dosimetry results were compared with ex vivo biodistribution data and S-values based on the MIRD formalism.

Results: The normal brain, brain tumors, and right flank tumor uptake were determined at all timepoints and compared with ex vivo biodistribution at the last timepoint, Mouse 1: 0.96, 6.96, and 3.60 %ID/g, and ex vivo 0.51, 6.67, and 3.98 %ID/g, Mouse 2: 0.53, 6.92, and 3.14 %ID/g, and ex vivo 0.36, 5.39, and 4.23 %ID/g, respectively. The RAPID integrated mean absorbed doses were estimated and compared with S-values integrated doses, Mouse 1: 0.20, 1.21, and 0.66 Gy/MBq, and S-values 0.18, 1.34, and 0.71 Gy/MBq, Mouse 2: 0.12, 1.32, and 0.62 Gy/MBq, and S-values 0.11, 1.34, and 0.62 Gy/MBq, respectively. The comparison results showed good agreement.

Conclusion: High-resolution voxel-wise dosimetry in mice gliomas treated with 177Lu-NM600 was successfully performed in the RAPID platform. This extension of RAPID will facilitate future preclinical studies that utilize micro-SPECT/CT to evaluate novel RPT agents.

Funding Support, Disclosures, and Conflict of Interest: NIH National Cancer Institute (NCI), grant P01CA250972.

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