Theranostics is a personalised Nuclear Medicine approach that uses closely related radiopharmaceuticals to identify and treat specific molecular targets on cancer cells. The term combines “therapy” and “diagnostics”, reflecting the principle of using diagnostic imaging to determine whether a targeted radioactive treatment is likely to reach a patient’s cancer.During the diagnostic stage, a small amount of a radiopharmaceutical is administered, usually through a vein. The targeting molecule binds to a particular receptor or protein on cancer cells, while the attached radioactive tracer allows these cells to be seen on PET-CT or SPECT-CT imaging. If the scan shows sufficient uptake in the tumours, a related therapeutic radiopharmaceutical may be used to deliver a higher dose of radiation directly to those cells.Established theranostic approaches include somatostatin receptor-targeted imaging and therapy for selected neuroendocrine tumours, and prostate-specific membrane antigen (PSMA)-targeted imaging and therapy for selected prostate cancers. The diagnostic and therapeutic radiopharmaceuticals are not necessarily identical, but they target the same molecular feature.
- Well-differentiated neuroendocrine tumours that express somatostatin receptors
- Neuroendocrine tumours that are locally advanced, inoperable or metastatic
- Advanced prostate cancer that expresses PSMA on molecular imaging
- Selected patients with metastatic castration-resistant prostate cancer
- Patients whose cancer has progressed despite or after other recommended prostate cancer treatments
- Patients with disease in multiple locations that can be reached by a circulating radiopharmaceutical
- Selected patients who require a targeted systemic treatment rather than treatment of only one tumour site
- Patients who have adequate bone marrow, kidney and liver function to receive the planned therapy
- Patients whose overall health and previous treatments allow radiopharmaceutical therapy to be administered safely
How Theranostics Is Performed
Before Treatment
The Nuclear Medicine physician reviews the diagnosis, biopsy findings, molecular imaging, previous treatments, symptoms and medical history.
The cancer’s extent and molecular target expression are assessed using an appropriate PET-CT or SPECT-CT scan.
For neuroendocrine tumours, somatostatin receptor imaging may be used to determine whether the tumours are sufficiently receptor-positive.
For prostate cancer, PSMA PET-CT may be used to assess whether the disease shows adequate PSMA expression.
Additional CT, MRI, bone imaging or other tests may be reviewed to understand the overall disease burden.
Blood tests are performed to assess blood counts, kidney function, liver function and other relevant measurements.
Current medicines, previous chemotherapy or radiation exposure and other medical conditions are reviewed.
Pregnancy and breastfeeding must be discussed because radioactive material is used.
Patients who may conceive or father a child receive specific advice about contraception and the period for which pregnancy should be avoided.
Hydration, fasting and medication instructions are provided according to the radiopharmaceutical being used.
Medicines that could interfere with imaging or treatment may need to be adjusted under specialist guidance.
The expected number and timing of treatment cycles, possible benefits, side effects and radiation-safety precautions are explained.
Individualised dosimetry may be performed in selected patients to estimate radiation absorbed by the tumours and healthy organs.
During Treatment
The patient is admitted to the Nuclear Medicine treatment area, either as a day-care patient or for a hospital stay, depending on the radiopharmaceutical and applicable regulations.
An intravenous line is placed to administer fluids, medicines and the therapeutic radiopharmaceutical.
Hydration may be provided before, during or after treatment.
During selected treatments for neuroendocrine tumours, an amino-acid infusion is administered to help reduce radiation exposure to the kidneys.
Anti-nausea medicines may be given before an amino-acid infusion or radiopharmaceutical treatment.
The therapeutic radiopharmaceutical is administered slowly through the intravenous line.
The targeting molecule carries the radioactive substance through the bloodstream to cells expressing the relevant receptor or protein.
Radiation emitted by the radiopharmaceutical damages the targeted cancer cells.
The patient’s vital signs and response are monitored during and after administration.
Post-treatment imaging may be performed to confirm the distribution of the radiopharmaceutical and support dosimetry.
Treatment is commonly delivered in multiple cycles separated by several weeks, although the schedule depends on the radiopharmaceutical and individual treatment plan.
After Treatment
The patient is monitored for immediate reactions before leaving the treatment area or hospital.
Hydration is encouraged, where appropriate, to help the body remove unbound radiopharmaceutical through the urine.
Patients are generally advised to empty their bladder frequently and follow careful toilet and personal-hygiene measures.
Temporary radiation-safety precautions are provided in writing.
Precautions may include maintaining a specified distance from others, limiting prolonged close contact, sleeping separately and avoiding close contact with children or pregnant people.
The required precautions and their duration depend on the radiopharmaceutical, administered activity and applicable radiation-safety guidance.
Mild tiredness, nausea, reduced appetite or a temporary increase in pain may occur following treatment.
Blood tests are performed between cycles to monitor blood counts, kidney function and liver function.
Each subsequent cycle is given only after the patient has been reassessed and remains suitable for treatment.
Follow-up may include PET-CT, SPECT-CT, CT, MRI, tumour markers, hormone-related markers or other tests appropriate to the cancer.
Additional treatment cycles, a pause in treatment, dose modification or another cancer treatment may be recommended according to response and side effects.
Potential Benefits of Theranostics
- Selection of treatment based on whether the molecular target is visible on diagnostic imaging
- Delivery of radiation to cancer cells expressing a specific receptor or protein
- Treatment of tumours in multiple parts of the body through a systemically administered radiopharmaceutical
- Reduced radiation exposure to many non-target tissues compared with non-targeted radiation delivery
- A personalised approach based on the individual cancer’s biological characteristics
- The ability to visualise where the diagnostic and therapeutic agents are likely to travel
- Post-treatment imaging to confirm radiopharmaceutical distribution
- The potential to control tumour growth or reduce tumour burden
- Relief of cancer-related symptoms in selected patients
- A treatment option for some cancers that have progressed despite other therapies
- The ability to deliver treatment in planned cycles and reassess the patient between cycles
- Individualised dosimetry in selected cases
- The ability to integrate treatment with systemic therapy, surgery, external radiation therapy or other cancer treatments when appropriate
Side Effects of Theranostics
- Tiredness or weakness
- Nausea or vomiting
- Reduced appetite
- Mild abdominal discomfort
- Temporary increase in tumour-related or bone pain
- Dry mouth or changes in taste, particularly with some PSMA-targeted treatments
- Reduced production of saliva
- Temporary hair thinning in some patients
- Reduction in red blood cells, causing anemia
- Reduction in white blood cells, increasing infection risk
- Reduction in platelets, increasing bleeding or bruising risk
- Temporary or persistent bone-marrow suppression
- Changes in kidney and liver function
- Electrolyte disturbances or nausea related to protective amino-acid infusions
- Hormonal symptoms caused by the release of substances from certain neuroendocrine tumours
- Rare severe hormonal crisis in patients with functioning neuroendocrine tumours
- Rare longer-term bone-marrow disorders, including myelodysplastic syndrome or leukemia
- Reduced fertility or potential effects on reproductive health
- Incomplete response or continued cancer progression despite treatment
