MetaIodoBenzylGuanidine (mIBG) [update]

This entry is part 1 of 3 in the series "Radiation" --


[Update to the Update: On 24July2015 after his cancer had relapsed, another mIBG scan was performed. This time, the cancer was shown to be mIBG avid]

[Update: On 4Sept2014, during the imaging 123-mIBG, it was determined that Liam’s Neuroblastoma is one of the types that does not take up mIBG. This means that he will be excluded from participation of the 131-mIBG study and we will be performing more chemo treatments]

Let’s not leave out the cool science.  During the course of his treatment Liam will encounter mIBG (MetaIodoBenzylGuanidine).  The first time that he encounters it, should all go well, is this week (~4Sept2014). He will be injected with the chemical so that his Neuroblastoma can be imaged. So, how does it work? It turns out that Neuroblastoma has a strong affinity for this compound in about 85% of cases.[1] In a very high percentage, the Neuroblastoma cells will take this compound up while the normal cells will not. This is called ‘selectivity’. (i.e. the Neuroblastoma soaks this compound up selectively over normal cells).  mIBG in itself, however, doesn’t do anything. It is taken into the cell, and then is excreted from the cell at a later time.  This means that the Neuroblastoma cells are not sensitive to the compound. 

A clever and ingenious pupil of chemistry can already see what to do next.  Swapping out the Iodine atom on this compound with the radioactive version  makes this molecule very useful.


123 Iodine will decay by electron capture to form 123 Tellurium which will then emit a Gamma ray with an energy of 159 keV. This is useful for imaging.  This is like having an x-ray performed, but rather than having an x-ray source shining high energy light through Liam, the light will be generated inside him!  Since this radioactive atom is attached to a compound which is only selective to Neuroblastoma, Gamma rays (like x-rays) will be generated only at the Neuroblastoma sites.  With the correct detector, the Neuroblastoma will light up like a Christmas tree.


If 131 Iodine is used, different results will be observed.  131 Iodine decays in the follow two manners (statistically a 90% Beta(-) Decay and a 10% Gamma decay):

(Beta(-) Decay ~90%) {^{131}_{53}\mathrm{I}} \rightarrow \beta + \bar{\nu_e} + {^{131}_{54}\mathrm{Xe}^*}  + 606 keV 

(Gamma Decay ~10%) {^{131}_{54}\mathrm{Xe}^*}  \rightarrow {^{131}_{54}\mathrm{Xe}} + \gamma  + 364 keV

The Beta(-) decay produces a very energetic electron and an Antineutrino which have a tissue penetration of about 0.6 to 2 mm. This is enough energy to destroy cells. (i.e. a cell sized atomic bomb) So in essence, this gives a pathway for the mIBG, which is very selective to the Neuroblastoma, to blow up the cells (and leave the good cells alone)

This mIBG therapy is typically only given in cases of Nueroblastoma that have relapsed, however, we may be one of the lucky families that gets this treatment as a clinical trial directed at making this part of the standard treatment.  If everything works out well, we will be part of this trial sometime after 5 or 6 chemotherapy treatments.

This mIBG scan being performed this week will only involve 123 Iodine for gamma ray imaging. This will indicate all of the places that the Nueroblastoma has metastasized to. It will be used as a baseline for how he is progressing in his treatment later on.

  1. According to “…Roughly 80-85% of neuroblastomas will absorb MIBG. There are really 2 ways in which MIBG treatment is used. In both methods, the MIBG chemical is attached to an iodine molecule that has been made radioactive. The radioactivity can be either a low-dose or a high-dose…. ”
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