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Can occult metastases be Treated by radioimmunotherapy?
Author(s) -
Dunn Robert M.,
Juweid Malik,
Sharkey Robert M.,
Behr Thomas M.,
Goldenberg David M.
Publication year - 1997
Publication title -
cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.052
H-Index - 304
eISSN - 1097-0142
pISSN - 0008-543X
DOI - 10.1002/(sici)1097-0142(19971215)80:12+<2656::aid-cncr42>3.0.co;2-8
Subject(s) - radioimmunotherapy , nuclear medicine , medicine , imaging phantom , absorbed dose , lesion , single photon emission computed tomography , radionuclide therapy , dosimetry , radiology , monoclonal antibody , pathology , antibody , immunology
BACKGROUND Tumor lesions in the millimeter (mm) range may escape detection with nuclear medicine imaging methods (including single photon emission computed tomography [SPECT]) using radiolabeled monoclonal antibodies (MoAbs). We hypothesized that these lesions still could receive a potentially therapeutic radiation absorbed dose, and therefore should be treated, despite the lack of detection. METHODS To simulate this situation, 2‐mm beads (0.004 mL) containing ∼1.15 μCi of iodine‐131 ( 131 I) were used. The beads were placed centrally in a 1200‐mL liver phantom containing ∼3 mCi of 131 I. The resultant activity concentration on the beads was ∼288 μCi/mL compared with ∼2.5 μCi/mL in the phantom, corresponding to a maximum tumor uptake of ∼0.3% injected dose per gram (%ID/g) if 100 mCi of 131 I‐labeled immunoglobulin G were administered. The phantom, containing the beads, was imaged by both planar and SPECT techniques at hypothetical Day 1 (time of maximum tumor uptake) and at hypothetical Day 7 to examine the improved target‐to‐nontarget ratio over time. In addition to imaging the beads, the radiation absorbed dose to the simulated lesions from the beta component emissions of 131 I was calculated using absorbed fractions based on Berger's point kernels. RESULTS Regardless of the conditions used, the beads could not be observed by either planar or SPECT imaging. However, the radiation‐absorbed dose to the simulated lesion was calculated to be as high as ∼6200 centigray (cGy), with an average dose rate of ∼89.5 cGy/hour. CONCLUSIONS This simulation demonstrates that a relatively high absorbed dose and dose rate can be delivered to mm‐sized lesions not observed by conventional nuclear imaging methods, and that these lesions should be considered for radioimmunotherapy with 131 I MoAbs. However, for micrometastases of <1 mm, other radionuclides with shorter path length β particles than 131 I, Auger electrons, or α particles should be considered. Cancer 1997; 80:2656‐9. © 1997 American Cancer Society.