Hepatic absorbed radiation dosimetry during I-131 metaiodobenzylguanidine (MIBG) therapy for refractory neuroblastoma.
OBJECTIVE
To compare the prediction of therapeutic hepatic radiation-absorbed dose rates from tracer imaging plus a linearity assumption to estimation based on intra-therapy imaging in (131)I metaiodobenzylguanidine (MIBG) therapy of refractory neuroblastoma.


METHODS
Conjugate-view images of the liver were obtained before therapy for seven patients at seven times after a tracer infusion of (131)I MIBG and at three times after the therapy infusion. Measured liver activities were converted to dose-rate estimates. Three statistical models of the rates assuming double exponential dependences on time were examined. One of the three models allowed for a multiplicative correction to the therapeutic late-phase dose-rate amplitude. Results from that model: (1) the tracer prediction of the late-phase absorbed-dose-rate amplitude was a factor of 1.75 times the intra-therapy-estimated value, and (2) the difference between tracer prediction of the radiation-absorbed dose and intra-therapy estimation of it was statistically significant, and (3) the liver radiation-absorbed dose did not reach 30 Gy.


CONCLUSIONS
A statistical modeling analysis finds that the radiation-absorbed dose after therapy appears to be lower than that which is predicted from the linear scaling with administered activity of the tracer radiation-absorbed dose. Hepatocyte toxicity is the most likely reason but it is not high enough to produce clinically observable results.
Koral
Kenneth F
KF
Department of Radiology, Nuclear Medicine Division, University of Michigan, Ann Arbor, MI, USA. kenkoral@umich.edu
Huberty
John P
JP
Frame
Bill
B
Matthay
Katherine K
KK
Maris
John M
JM
Regan
Denise
D
Normolle
Daniel
D
Yanik
Gregory A
GA
D019797:3-Iodobenzylguanidine / Q000008:administration & dosage / Q000378:metabolism / Q000627:therapeutic use*; D000042:Absorption; D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008099:Liver / Q000378:metabolism / Q000528:radiation effects*; D008297:Male; D008954:Models, Biological; D009447:Neuroblastoma / Q000473:pathology* / Q000532:radiotherapy*; D011829:Radiation Dosage; D011874:Radiometry
D019797:3-Iodobenzylguanidine