Does Radiation Therapy Weaken the Immune System?

For most healthy individuals, a fever or cough is bothersome but not deadly. However, if you are currently undergoing radiation therapy to treat cancer, infections may lead to severe and potentially life-threatening illnesses.

That’s because radiation therapy often weakens the immune system, compromising a patient’s ability to fight off the common cold, influenza (the flu), and even COVID-19.

Here, we offer more insight into how radiotherapy affects the immune system and tips for improving your immunity during and after treatment.

Radiotherapy uses high doses of radiation to target cancer cells. Though treatment is typically localized, healthy cells near the cancerous areas can sometimes be damaged too.

If stem cells in bone marrow are damaged by radiotherapy, the body will struggle to produce white blood cells (WBCs). Also known as leukocytes, WBCs are responsible for attacking disease-causing pathogens like bacteria, viruses, parasites, and fungi.

When your white blood cell count is low – a condition called leukopenia – you are at an increased risk for infection.

Radiotherapy can also weaken immunity by compromising your body’s first line of defense: the skin.

Your skin forms a physical barrier against germs. Unfortunately, high doses of radiation can injure the skin by creating open sores through which germs can enter the body.

The extent that radiation therapy affects your immune system depends on various factors, including:

• The total radiation dose
• The radiation schedule
• Which part of the body is being treated
• How much of the body is being treated

Higher radiation doses are more likely to cause severe side effects, including the potential for lessened immunity.

Radiation directed toward bones is also more likely to compromise immunity since white blood cell production occurs in bone marrow.

However, patients receiving radiation to their entire body (called total body irradiation) are at the highest risk for suppressed immunity.

Like radiation therapy, the goal of chemotherapy is to target and destroy cancer cells. However, there are important differences between the two treatment options.

Whereas radiotherapy is localized to the area with cancer, chemo is systemic. That means your entire body is affected by anti-cancer drugs.

Because of this, chemotherapy is more likely to weaken your immune system than radiotherapy.

If your cancer care team suggests a combination of both chemo and radiation therapy, your risk for immune system suppression will be heightened.

Patients receiving radiotherapy or who recently finished radiotherapy treatment are more prone to certain infections.

These infections are called opportunistic infections because they typically occur in individuals with compromised immune systems.

Opportunistic infections can be caused by bacteria, viruses, fungi, or protozoa. Common types of infections include:

• Staphylococcus (staph): Staph infections cause bumps, redness, and swelling on the skin. They are often mild and can be treated with antibiotics.
• Streptococci (strep): Strep causes tonsillitis and cellulitis. Both are relatively mild and can be treated with antibiotics.
• Enterococci: These bacteria can contribute to urinary tract infections, wound infections, a heart infection called endocarditis, and sepsis.

• Candidiasis (thrush): Thrush causes white patches and soreness in the mouth. Your cancer care team may prescribe antifungal pills or an injection. Candidiasis can also cause vaginal thrush (yeast infection), which is treated with antifungal creams.
• Aspergillosis: This fungus can cause a serious lung infection that must be treated with an IV drip.
• Pneumocystis: The pneumocystis fungus can cause pneumocystis pneumonia, a severe lung infection that leads to fluid buildup. Oral antifungal medications are the typical course of treatment.

• Common Colds: If your immune system is compromised, a common cold can lead to bronchitis or pneumonia.
• Herpes Simplex: This virus causes cold sores and genital herpes. There is no cure, but treatment can lessen symptoms.
• Varicella Zoster (chickenpox): The chickenpox virus can cause potentially fatal infections in oncology patients. Luckily, there are antiviral drugs available.
• Cytomegalovirus (CMV): Most people who contract CMV experience mild symptoms like fever and sore throat. But the virus can cause infections in oncology patients.
• Influenza (flu): Cancer patients can develop life-threatening complications if they contract the flu.
• SARS-CoV-2 (COVID-19): Oncology patients have an increased risk of contracting COVID-19. Vaccines and boosters can help mitigate severe illnesses.

Protozoan infections are caused by single-celled parasites called protozoa. These parasites enter the body through insect bites or infected food or water, causing a condition called toxoplasmosis.

Toxoplasmosis can feel like the flu. However, if your immune system is compromised, it can cause symptoms like seizures and encephalitis.

To prevent illness while receiving radiotherapy, you must take certain precautions.

These include:

• Getting the flu shot each year
• Receiving COVID-19 vaccinations
• Washing your hands with water and soap
• Wearing a mask in public
• Avoiding sick people and large crowds
• Social distancing
• Avoiding unpasteurized dairy, cooking meat well, and washing produce
• Treating cuts and scrapes properly

Your cancer care team may also suggest filgrastim. This medication helps your blood marrow produce WBCs.

Many people believe that once they finish radiotherapy treatment, their immune system will quickly return to normal. Unfortunately, this is not the case.

According to recent research published in the National Library of Medicine, oncology patients experience a “significant impairment in immune recovery following cancer treatment.”

More specifically, radiation therapy was shown to significantly delay the recovery of interleukin 4 (IL4). IL4 is a protein that stimulates the activation of B cells, a type of lymphocyte that creates antibodies. IL4 also affects the behavior of T cells, which protect the body from infection.

Luckily, you can help your immune system recover by following common sense practices such as:

• Eating a balanced diet rich in fruits and vegetables
• Eliminating tobacco and avoiding alcohol
• Limiting stress
• Exercising regularly
• Sleeping 7 to 8 hours per night

At SERO, our expert radiation oncologists and care teams are here to help you navigate your cancer journey, from diagnosis to remission. This includes helping you understand how radiotherapy may affect your immune system.

Whether you have a question about boosting your white blood cell count or mitigating the risk of infection during treatment, we are here to provide kind and compassionate support.

To learn more about SERO and our radiation services, call us at 704-333-7376.