¹²³I-MIBG Versus ¹⁸F-FDG: Which Is Better, or Which Can Be Eliminated?

TO THE EDITOR: The excellent paper by Dr. Sharp and colleagues compared the diagnostic utility of ¹²³I-metaiodobenzylguanidine (MIBG) with ¹⁸F-FDG (1). They found that ¹⁸F-FDG is superior to ¹²³I-MIBG in stage 1 and 2 neuroblastoma and that ¹²³I-MIBG is superior to ¹⁸F-FDG in stage 4 neuroblastoma.

The authors comment that for socioeconomic and radiation exposure reasons, a reduction in the total number of imaging procedures may be desirable in neuroblastoma patients. In this setting, what is important is not necessarily which test is superior. Rather, we want to know if one of these imaging tests can be safely eliminated. The answer is no. Not in early-stage neuroblastoma, and not in late-stage neuroblastoma.

The authors found that in 10 of 10 patients with early disease, ¹⁸F-FDG was equivalent or superior to ¹²³I-MIBG. But the 95% confidence interval for this ranges from about 72% to 100%. Thus, it remains statistically possible that ¹⁸F-FDG may be inferior to ¹²³I-MIBG in up to 3 of 10 patients. We thus conclude that ¹²³I-MIBG scanning cannot be safely eliminated in early neuroblastoma, although ¹⁸F-FDG works particularly well.

In stage 4 disease, ¹²³I-MIBG was superior in 24 of 40 patients, whereas ¹⁸F-FDG was better in 8 of 40 patients. Yes, 24 of 40 is different from 8 of 40 (P < 0.001), but so what? The more pressing question is whether 8 of 40 is significantly different from 0 of 40. That is, can we safely eliminate ¹⁸F-FDG scanning in stage 4 patients? No. Their data indicate that up to 3 of 10 late-stage patients will benefit from ¹⁸F-FDG scanning, even though ¹²³I-MIBG performs better.

The authors make a valuable contribution by giving us the relative superiority of each agent during the course of neuroblastoma. However, their data also indicate that ¹²³I-MIBG scanning cannot yet be safely eliminated, nor can ¹⁸F-FDG scanning be safely eliminated, in the evaluation of early- or late-stage neuroblastoma.