[Radioisotope therapy of malignant pheochromocytoma with iodine-131 metaiodobenzylguanidine--absorbed dose assessments using SPECT].

The correlation of absorbed doses D (rad) of tumors in 4 patients with malignant pheochromocytoma, who were treated by 131I-MIBG (3.7 GBq), with their clinical courses were analyzed and the clinical significance of determination of absorbed dose was discussed. Absorbed doses of 131I-MIBG in the tumors were measured by using SPECT at the time of therapy. Absorbed dose was calculated based on the MIRD (medical internal radiation dose committee) equation. Tumor volumes were ranged from 17 g-100 g (mean 40 g), effective half lives were ranged from 1.3 days-5.9 days (mean 3.6 days), and tumor absorbed doses were varied between 5.4 Gy-68 Gy (mean 40 Gy). When the absorbed doses of the tumor exceeded over 40 Gy, good clinical responses were obtained. The initial treatment seemed to be important for 131I-MIBG therapy, since the absorbed doses in the following therapy became reduced. These results indicate that the quantitative SPECT for radioisotope therapy is clinically valid and that the calculated absorbed doses correlate well with clinical responses.