TY - JOUR T1 - Tumor Response After [<sup>90</sup>Y-DOTA<sup>0</sup>,Tyr<sup>3</sup>]Octreotide Radionuclide Therapy in a Transplantable Rat Tumor Model Is Dependent on Tumor Size JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1841 LP - 1846 VL - 42 IS - 12 AU - Marion de Jong AU - Wout A.P. Breeman AU - Bert F. Bernard AU - Willem H. Bakker AU - Theo J. Visser AU - Peter P.M. Kooij AU - Arthur van Gameren AU - Eric P. Krenning Y1 - 2001/12/01 UR - http://jnm.snmjournals.org/content/42/12/1841.abstract N2 - A promising application of radiolabeled somatostatin analogs is peptide receptor–targeted radionuclide therapy of somatostatin receptor–expressing tumors. A suitable radionuclide is 90Y, which emits high-energy β-particles with a pathlength of several millimeters in tissue, making it especially promising for treatment of large tumors. Methods: We investigated the radiotherapeutic effect of different activities (111 and 370 MBq) of [90Y-1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (DOTA)0,Tyr3]octreotide in Lewis rats bearing somatostatin receptor–positive rat pancreatic CA20948 tumors of different size (0.08–15 cm2) in their flank. Results: Dose-dependent radiotherapeutic effects of 90Y-labeled octreotide in this rat tumor model were found. Tumor control (100% complete response) was found in animals bearing tumors of 3–9 cm2 (mean, 7.8 cm2) after intravenous injection of the highest activity (370 MBq [90Y-DOTA0,Tyr3]octreotide). In rats bearing tumors of ≤1 cm2 or ≥14 cm2, the effects were less pronounced (50% and 0% complete response, respectively). In tumors of ≤1 cm2 the 90Y radiation energy will not be absorbed completely in the tumor, whereas in tumors of ≥14 cm2 the increased number of clonogenic and probably hypoxic tumor cells may explain the failure to reach a cure. Conclusion: This study shows the ability of [90Y-DOTA0,Tyr3]octreotide to control tumor growth, especially in medium-sized tumors. The effect of radionuclide therapy appeared to be dependent on tumor size at the onset of therapy. ER -