(131)I-MIBG treatment of pheochromocytoma: low versus intermediate activity regimens of therapy.

Since the second half of the 1980s, (131)I-MIBG has been widely used for treatment of patients with malignant pheochromocytoma. In 1991, at the International Meeting in Rome, it was agreed that (131)I-MIBG therapy induces significant tumor responses in about 30-50% of cases, long-term stabilization of disease in several cases and significant reduction of cathecolamine-related symptoms in almost all patients. Nevertheless, more than 20 years later, its therapeutic use in malignant phaeochromocytoma has not yet been standardized. Aim of the present study was to compare the use of low versus intermediate activity of MIBG to achieve better results in a shorter time with higher activities.Two different modalities of (131)I-MIBG therapy were performed: before 2001, 12 patients (Group 1) received a fixed activity of 5.55 GBq/session. From 2001 to 2009, 16 patients (Group 2) were treated with 9.25-12.95 GBq/session.As expected, the overall response rate in Group 2 are slightly better. The most important result of increasing the single session activity was the shorter median time to achieve a significant response (7 versus 19 months), which was obtained with a lower median cumulative activity (11 versus 22 GBq) in a lower median number of sessions (2 versus 7).We demonstrated that intermediate single session activity shortened to one third the global treatment time, with similar efficacy and a moderate increment of toxicity. Consequently, the increase of (131)I-MIBG activity, without reaching myeloablative levels, can be recommended for standard treatment of pheochromocytoma and paraganglioma patients.