Sci—Thur AM: YIS - 03: irtGPUMCD: a new GPU-calculated dosimetry code for 177Lu-octreotate radionuclide therapy of neuroendocrine tumors

Authors

  • Montégiani Jean-François,

    1. Physics, Engineering Physics and Optics, Université Laval, Quebec City, QC, Canada
    2. Molecular Imaging and Targeted Therapeutics, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
    3. Radiology, Université Laval, Quebec City, QC, Canada
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  • Gaudin Émilie,

    1. Physics, Engineering Physics and Optics, Université Laval, Quebec City, QC, Canada
    2. Molecular Imaging and Targeted Therapeutics, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
    3. Radiology, Université Laval, Quebec City, QC, Canada
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  • Jackson Price A.,

    1. Physics, Engineering Physics and Optics, Université Laval, Quebec City, QC, Canada
    2. Molecular Imaging and Targeted Therapeutics, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
    3. Radiology, Université Laval, Quebec City, QC, Canada
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  • Beauregard Jean-Mathieu,

    1. Physics, Engineering Physics and Optics, Université Laval, Quebec City, QC, Canada
    2. Molecular Imaging and Targeted Therapeutics, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
    3. Radiology, Université Laval, Quebec City, QC, Canada
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  • Després Philippe

    1. Physics, Engineering Physics and Optics, Université Laval, Quebec City, QC, Canada
    2. Molecular Imaging and Targeted Therapeutics, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
    3. Radiology, Université Laval, Quebec City, QC, Canada
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Abstract

In peptide receptor radionuclide therapy (PRRT), huge inter-patient variability in absorbed radiation doses per administered activity mandates the utilization of individualized dosimetry to evaluate therapeutic efficacy and toxicity. We created a reliable GPU-calculated dosimetry code (irtGPUMCD) and assessed 177Lu-octreotate renal dosimetry in eight patients (4 cycles of approximately 7.4 GBq).

irtGPUMCD was derived from a brachytherapy dosimetry code (bGPUMCD), which was adapted to 177Lu PRRT dosimetry. Serial quantitative single-photon emission computed tomography (SPECT) images were obtained from three SPECT/CT acquisitions performed at 4, 24 and 72 hours after 177Lu-octreotate administration, and registered with non-rigid deformation of CT volumes, to obtain 177Lu-octreotate 4D quantitative biodistribution. Local energy deposition from the β disintegrations was assumed. Using Monte Carlo gamma photon transportation, irtGPUMCD computed dose rate at each time point. Average kidney absorbed dose was obtained from 1-cm3 VOI dose rate samples on each cortex, subjected to a biexponential curve fit. Integration of the latter time-dose rate curve yielded the renal absorbed dose.

The mean renal dose per administered activity was 0.48 ± 0.13 Gy/GBq (range: 0.30–0.71 Gy/GBq). Comparison to another PRRT dosimetry code (VRAK: Voxelized Registration and Kinetics) showed fair accordance with irtGPUMCD (11.4 ± 6.8 %, range: 3.3–26.2%). These results suggest the possibility to use the irtGPUMCD code in order to personalize administered activity in PRRT. This could allow improving clinical outcomes by maximizing per-cycle tumor doses, without exceeding the tolerable renal dose.

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