
One of the difficulties of direct injection of radioisotope into a tumor, is the absorption of the radioisotope from the site and its distribution to other body tissues.  

Studies of biodistribution and therapeutic action were carried out on the effect of a single intratumoral dose of chromic phosphate, carrying the radioisotope 32P, in large particle size, for the treatment of solid tumors. Therapeutic action showed a 50% reduction in tumor size.  Biodistribution studies showed that approximately 50% remains in the tumor, 10% [+/- 5%] in the liver, 30% eliminated in feces and 7% in urine.  Large colloidal particles of chromic 32-P are not safe enough for intratumoral injection, since it is mobilized from the injection site and delivers a high dose to the entire organism.  [23]

"Human macroaggregated albumin (MAA), ... labeled with technetium-99m (99mTc) ... was directly labeled with yttrium-90 (90Y)-acetate. This study evaluated whether 90Y-MAA could be potential radiotherapeutic agent for regional radiotherapy against malignant tumors. ... Following the intratumoral administration of 90Y-MAA, ... in nude mice bearing human neuroblastoma ... More than 93% of the radioactivity of the injected dose was found on the subcutaneous tumor over 168 h. ... A slight increase in radioactivity was noted in the liver, kidneys, and spleen over the 168-h periods. In conclusion, 90Y-MAA may be a potential agent for regional radiotherapy ... because of the sufficient persistence in the tumor following an intratumoral administration."[20]

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