Dosimetric quantities of neuroendocrine tumors over treatment cycles with 177Lu-DOTA-TATE

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Tumor dosimetry was performed for 177Lu-DOTA-TATE with the aims of better understanding i) the range and variation of the tumor absorbed doses (ADs), ii) how different dosimetric quantities evolve over the treatment cycles, and iii) whether this evolution differs depending on the tumor grade. Such information is important for radiobiological interpretation and may inform the design of alternative administration schemes. Methods: Data come from 41 patients with neuroendocrine tumors (NETs) of grade 1 (n = 23) or 2 (n = 18), that had received between 2 and 9 treatment cycles. Dosimetry was performed for 182 individual lesions, giving in total 880 individual AD assessments across all cycles. Hybrid planar-SPECT/CT imaging was used, including quantitative SPECT reconstruction, voxel-based absorbed-dose-rate calculation, semi-automatic image segmentation, and partial-volume correction. Linear mixed-effect models were used to analyze changes over cycles in tumor ADs, absorbed-dose rates and activity concentrations at day-1, effective half-times, and tumor volumes. Tumors smaller than 8 ml were excluded from analyses. Results: Tumor ADs ranged between 2 and 77 Gy per cycle. On average the AD decreased over the cycles, with significantly different rates (P < 0.05) for grade 1 and 2 NETs of 6% and 14% per cycle, respectively. The absorbed-dose rates and activity concentrations at day-1 decreased by similar amounts. The effective half-times were less variable but shorter for grade 2 than grade 1 (P < 0.001). For grade 2 NETS the tumor volumes decreased, with a similar tendency in grade 1. Conclusion: The tumor AD, absorbed-dose rate and activity uptake decrease, in parallel with tumor volumes, between 177Lu-DOTA-TATE treatment cycles, particularly for grade 2 NETs. The effective half-times vary less but are lower for grade 2 than grade 1 NETs. These results may indicate the development of radiation-induced fibrosis and could have implications for the design of future treatment and dosimetry protocols.

Original languageEnglish
Pages (from-to)399-405
Number of pages7
JournalJournal of Nuclear Medicine
Issue number3
Early online date2021
Publication statusPublished - 2022 Mar

Bibliographical note

Copyright © 2021 by the Society of Nuclear Medicine and Molecular Imaging, Inc.

Subject classification (UKÄ)

  • Radiology, Nuclear Medicine and Medical Imaging
  • Cancer and Oncology
  • Other Physics Topics


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