A radioconjugate consisting of the tumor-specific amino acid derivative 4-iodo-L-phenylalanine labeled with iodine I 131, a beta emitting radionuclide, with potential antineoplastic activity. Upon administration, iodine I 131 IPA actively crosses the blood-brain barrier and accumulates specifically in gliomas, via the amino acid transport system l-amino acid transporter 1 (LAT1) over-expressed in malignant glioma cells. where it delivers a cytotoxic dose of beta radiation. Cells that are exposed to radiation may also release potent toxins into the intracellular environment, leading to radiation-induced biological bystander effects (RIBBE) and killing cells not directly exposed to the radiation. Iodine I 131 IPA may also act synergistically with external irradiation due to its radiosensitizing property.