Targeted Radionuclide Therapy– A Precision Tool for Cancer Therapy

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Targeted radionuclide therapy, also called molecular radiotherapy or unsealed source radiotherapy, is a type of targeted therapy that uses radioactive substances, known as radiopharmaceuticals, to treat certain medical conditions like cancer.

This therapy involves the use of physical, biological, and chemical properties of the radiopharmaceuticals to target specific areas of the body for radiation treatment.

The radioactive substances are introduced into the body in different ways like ingestion or injection and are localized to specific locations, tissues, or organs depending on their administration routes and properties.

In this article, we will be discussing in detail targeted radionuclide therapy.

How does targeted radionuclide therapy work?

• The radiopharmaceuticals used in targeted radionuclide therapy contain a targeting molecule like peptide or antibody and a medical radioisotope, conjugated by a chelating agent.
• This targeting molecule binds to a tumor-specific receptor or antigens, based on the lock and key principle. This targeting molecule is used for both therapy and diagnosis, also known as theranostics, in most cases, with only a need to change the radioisotope.
• The targeting molecule is conjugated to a radioactive isotope, like Lutetium-177, Yttrium-90, Radium-223, etc., to create a targeted radiopharmaceutical. 
• After administration, the radiopharmaceutical will circulate throughout the body and bind specifically to the cancer cells to deliver targeted radiation to the tumor.
• The radiation that is emitted by the radioactive isotope will lead to localized ionization events leading to DNA damage, production of reactive oxygen species, and cell death.

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How are radioactive isotopes chosen for TRT?

The choice of the radioactive isotope will vary depending on the specific properties needed for proper treatment, like the energy and type of radiation emitted, chemical compatibility with the targeting molecule, and its half-life.

Radioisotopes having short half-lives are used in cases of diagnostic applications. The images of body organs and lesions can be obtained and diagnosis of diseases can be made in their early stages using extremely sensitive molecular imaging technologies such as PET (Positron Emission Tomography) and SPECT (Single Photon Emission Tomography).

For treatment purposes, medical radioisotopes having longer half-lives are preferred for treatment. Minimal cytotoxic doses of ionizing radiation need to reach the tumor site before decay to destroy the tumor. An exact localization of the toxicity is needed to ensure that the surrounding healthy tissues are minimally damaged or not damaged at all.

What is the procedure for TRT ?

TRT treatment may be provided intravenously or orally to the patient.

• In case of an intravenous approach, the patient will be admitted for a day in the hospital and will be administered saline or amino acid infusions along with the TRT. This is a painless procedure and leads to minimal or no side effects. The patient will be monitored after TRT, and a scan will be taken 24 hours after treatment.
• An example of an oral form of TRT is radioiodine therapy provided in patients having thyroid cancer. This involves providing the patient with an Iodine-131 radioisotope orally in the form of a liquid. This procedure is also painless. The patient is usually admitted one or two days before the procedure for radiation safety and to avoid radiation exposure to the family members of the patient.

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Which conditions can be treated using targeted radionuclide therapy?

Targeted radionuclide therapy may be used to treat the following conditions:

• Iodine-131 is the most common type of TRT used to treat benign thyroid conditions like thyrotoxicosis and malignant thyroid conditions like papillary thyroid cancer.
• Strontium-89 chloride, Radium-223 chloride, and Samarium-153 EDTMP are used for treating secondary cancer in bones and bone metastasis.
• Beta emitting phosphorus-32 is used for treating bone marrow conditions like overactive bone marrow. ( Know more about- What is Bone Marrow Transplant? )
• Yttrium-90 spheres can be used for treating primary and metastatic liver tumors.
• Yttrium-90 colloid suspension can be used to treat knee joint inflammation.
• Iodine-131 mIBG can be used for treating conditions like neuroblastoma and pheochromocytoma.
• Lutetium-177 can help in treating neuroendocrine tumors.

What are the advantages of TRT ?

Targeted radionuclide therapy has many benefits over traditional forms of cancer treatments like external beam radiation therapy and chemotherapy. 

The advantages of target radionuclide therapy are:

• It allows radiation to be precisely delivered to the cancer cells while minimizing any damage to the surrounding healthy tissues.
• Lesser side effects and better quality of life for patients during treatment.
• Can help treat cancers resistant to conventional cancer therapies, like cancer cells with hypoxic or radiation-resistant characteristics.
• Can be personalized for individual patients depending on their specific cancer characteristics.
• Can treat patients with metastatic or disseminated diseases (when the disease or cancer spreads from one part of the body to another).
• One dose of TRT is effective in treating cancer that has spread to multiple locations in the body, unlike conventional radiation therapy.

What does the future of TRT look like?

The research on targeted radionuclide therapy is expanding rapidly and many clinical trials are on to investigate its efficacy and safety in different types of cancers. There are advancements in the targeting molecule design, isotope production, and dosimetry (determination of the radiation dosage) that have improved the therapeutic efficiency and safety of TRT in patients.

The combination of TRT with other forms of cancer treatments, like chemotherapy, immunotherapy, or targeted therapy, is showing improved treatment outcomes.

Conclusion

Targeted radionuclide therapy has shown tremendous promise over conventional radiation therapy by precisely targeting the tumor areas and causing minimal or no damage to the healthy surrounding tissues. Additionally, TRT has the added advantage of using theranostic approaches, which helps in combining diagnostic imaging and therapy in one radiopharmaceutical. TRT, therefore, holds a lot of potential for personalised medicine, diagnosis, and treatment monitoring in a patient. Get targeted radionuclide therapy done at the best hospital H N Reliance Hospital Mumbai.