Radioimmunotherapy

Radioimmunotherapy (RIT) employs immune proteins to deliver radioactivity as tracers or targeted therapies. The sterile, pyrogen-free radioantibody is intravenously injected into the tumor or body cavities like peritoneum or intrathecal space, delivering tumoricidal radiation doses. RIT is effective against radiosensitive tumors like leukemias and lymphomas, while solid tumors require higher radiation doses for response.

Pediatric solid tumors, like neuroblastoma in CNS, respond well to intrathecal RIT, but common solid tumors (pancreatic, melanoma, prostate, colon) show limited success with direct intravenous injections.

RIT targets antigens on neoplastic cell surfaces or stroma, and quantitative methods for radiation dose estimation are developed to personalize treatment and minimize toxicity.

Theranostics integrates diagnostic and therapeutic roles, using the same radioisotope for both. High-resolution PET/CT imaging with antibodies aids precise dosimetry for better patient selection and treatment planning.

RIT’s therapeutic principle involves selective tumor targeting over normal tissues, creating a therapeutic index. Though the ideal is exclusive tumor radiation, normal radiosensitive tissues are affected during targeting.

The major hurdle that must be overcome to achieve the full potential of RIT is delivering tumoricidal doses ranging from 3,000 to 5,000 cGy for the most radiosensitive tumors and up to 10,000 cGy for most radioresistant solid tumors. This respecting radiosensitive tissues such as kidneys, lungs, colonic mucosa and bone marrow receive less than 2000, 1500, 250 and 100 cGy, respectively.