TY - JOUR T1 - A Stylized Computational Model of the Rat for Organ Dosimetry in Support of Preclinical Evaluations of Peptide Receptor Radionuclide Therapy with <sup>90</sup>Y, <sup>111</sup>In, or <sup>177</sup>Lu JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1260 LP - 1269 VL - 45 IS - 7 AU - Mark W. Konijnenberg AU - Magda Bijster AU - Eric P. Krenning AU - Marion de Jong Y1 - 2004/07/01 UR - http://jnm.snmjournals.org/content/45/7/1260.abstract N2 - The therapeutic effects of peptide receptor–based radionuclide therapy are extensively being investigated in rats bearing tumors. Both the dose to the tumor and the therapy-limiting dose to normal tissues, such as kidneys and bone marrow, are of interest for these preclinical studies. The aim of this work was to develop a generalized computational model for internal dosimetry in rats. Methods: Mature rats were dissected and the relative positions, dimensions, and weights of all of their major organs were measured. A mathematic model was set up for the rat body and its internal organs to enable Monte Carlo radiation transport calculations to determine estimates for both tumor and organ self-doses as cross-organ doses for 90Y, 111In, and 177Lu. The organs and body were mostly of ellipsoid shape with the axes given as the measured length, width, and height normalized to values that, together with the measured weights, are consistent with the recommended soft-tissue and bone densities. A spheric tumor of 0.25 g was positioned on the right femur. Calculations were performed with the Monte Carlo neutral particle transport code MCNP for the β-emitters (maximum energy, 2.28 MeV) and 177Lu (maximum energy, 0.497 MeV) and for the γ-emissions from 177Lu and from 111In. The presented absorbed dose S values are used to calculate the absorbed dose estimates for the rat organs in a study on the biodistribution of 177Lu-DOTA-Tyr3-octreotate (DOTA is 1,4,7,10-tetraazadodecane-N,N′,N″,N‴-tetraacetic acid). Three activity distributions were considered in the kidney: uniform in the whole kidney, in the cortex, or in the outer 1-mm-thick rim of the cortex. Isodose curves and dose volume histograms were calculated for the dose distribution to the kidneys. Results: Depending on the activity distribution in the kidneys, the renal dose for 177Lu-DOTA-Tyr3-octreotate is 0.13–0.17 mGy/MBq. Conclusion: The renal dose of 70–95 Gy for an injected activity of 555 MBq will likely cause radiation damage, although the higher amount of peptide with this activity may influence the dosimetry by partial receptor saturation. Dose volume histograms show that 111In and 177Lu are likely to have a higher threshold for renal damage than 90Y. ER -