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Targeted Radionuclide Therapies

The rate at which Nuclear Medicine treatments have increased has been staggering. The efficacy with which these therapies can be delivered is world-class and no longer experimental. Indeed many private centers internationally now offer these services where it has become commonplace. With the advent of more targeted therapies the future of patient-tailored medicine looks viable and promising. The field of Theragnostic looks set to explode. The following common examples of Theragnostic services are cited:

 

Conventional therapies:

This includes radio-iodine ablation therapy for thyroid cancer and hyperthyroidism. To date private health facilities have be under-utilizing thyroid ablation therapy for cancer since the radiation doses prescribed were only given for the ablation of remnant (minimal) thyroid disease after surgery in stage 1 (early) thyroid cancer. The handling of high-dose open-source radiation for this condition requires a licensed Nuclear Physician and/or Nuclear Physicist e.g. advanced thyroid cancer. We aim to rectify this shortfall by working with the radiation oncologists to provide the best possible outcomes for patients with more advanced disease.

I-131 MIBG therapy for the palliation (easing of disease) of children with debilitating Neuroblastoma (and other MIBG-receptive tumors) is being used more frequently at an earlier stage and has shown effectivity in the prolongation of life and markedly improving symptoms. Promising trials have demonstrated that their earlier use markedly improves patient outcomes.

Novel injectable therapies:

Receptor-targeted therapy – Many malignancies (and more specifically neuroendocrine tumors) express receptors on their cell surfaces sensitive to the innate substance called Somatostatin. These receptors trigger a chain of events that cause very unpleasant symptoms. Typically chemotherapy has been very ineffectual for the most part in controlling the symptoms or causing any real remission. Substrates that bind to the receptors and subsequently the tumor cells can now be coupled to high energy radiation isotopes that cause local ablation of these tumors without affecting the surrounding tissues unlike general chemotherapy and local external beam radiation, which oftentimes also cause damage around the target or elsewhere in the body. This field of patient-tailored medicine is expanding rapidly to include other receptors found in other tumors.

Antigen-Antibody couple therapy (radio-immunotherapy) – Likewise, many cell lines express antigens on their surfaces unique to those tumors e.g. CD20 receptors on certain lymphoma cell lines. Common human antibodies that on their own have been used for targeting these cell lines can now be coupled to high energy radiation sources and injected intravenously to not only cause a local immune response in fighting these malignancies but also radiate them from  close proximity – the so called “double-effect”. This therapy is currently of limited availability in South Africa.

Bone seeking agents – Certain radio-isotopes are known to have a high affinity for areas of increased bone turnover e.g. at bone cancer and bone metastases from other cancers. It is a well-known fact that the most painful metastases known in cancer occur at these sites and are often not responsive to even high dose opioid therapy e.g. morphine and its derivatives. These aforementioned bone-seeking agents causes local killing of metastatic cells, but also general destruction of the sensitive nerve endings in this site to effectively and permanently alleviate pain in these patients.

Novel semi-invasive therapies:

Selective Internal Radiation Therapy – Colon cancer (and indeed many other cancers) metastasize predominantly to the liver. Unfortunately oftentimes the patient may be cancer free elsewhere following surgery but resection of the offending mass is impossible. By feeding a transarterial catheter into the blood supply of the tumor, microspheres coupled to high energy radiation can deliver radiation doses to the tumor that far exceed those possible in external beam radiation – again without offending the surrounding normal tissue. In fact in both liver cancer and colon cancer many patients have experienced remission and remarkably prolonged survival.

Radiosynovectomy – Patients with intractable joint pain (including hemophiliacs with pain and stiffness related to recurrent bleeding into the joint spaces), have demonstrated remarkable reduction in pain (and bleeding for hemophilia) by the injection of a radiopharmaceutical into the joint space. In fact it has been demonstrated to be less invasive than surgical synovectomy and equally effective. It is also much more effective than chemotherapy agents and has a lower complication rate than both the former. Furthermore it can be used for a variety of joint sizes and isn’t limited to medium-to-large joints only. Indeed many patients have been rendered pain free or were able to stop taking harmful pain medications such as corticosteroids and disease modifying drugs.

Ablation of arterial walls at transcutaneous stenting of coronary arteries – inflating a balloon catheter filled with radiation “bakes” the unstable plaque and decreases the rate of re-stenosis (reclogging) at stenting thus decreasing the risk of ischemia/infarction recurrence. Currently there is a lack of experience in using this type of therapy in South Africa.

Novel invasive therapies:

Intra-operative intra-tumoral injections – high dose radiation can be given intra-tumorally into well capsulated tumors (especially brain tumors) to deliver a localized high energy dose to the tumor and aid in-its shrinkage with the ultimate goal of excision.

There are many more novel therapies constantly in development that are beyond the scope of this description. Please contact us for more information.

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