Is radiation exposure safe for patients?

Radiation has been used in medicine for over a hundred years to help diagnose and treat diseases. Doctors and medical professionals only use radiation when they believe it will provide a medical benefit to the patient. Medical physicists play an important role in keeping patients safe by making sure the amount of radiation used is the minimum needed to diagnose a condition or treat a disease.

Medical physicists routinely perform safety checks on equipment and procedures to ensure that radiation-producing devices are working properly and that the correct amount of radiation is delivered. They work closely with the care team (for example, radiologists, radiation oncologists, radiation technologists, radiation therapists) to find the best way to deliver radiation safely. Medical physicists also calculate the amount of radiation dose a patient has received and can answer patients’ questions to help them feel informed and safe. In these ways they help keep radiation as safe as possible while maximizing its benefits for each individual patient.

For nearly all patients, medical procedures involving radiation are very safe. Potential risks from radiation are related to the amount of radiation dose received and whether it is received over the whole body or just a portion of the body. Usually, patients receive radiation to only a small part of their body. Radiation levels are low in diagnostic applications and higher for radiation therapy because the goal of therapy is to destroy harmful cells, such as cancer.

When assessing radiation risk from a medical exposure, there are two main considerations: the possibility that the body’s normal tissues will be noticeably damaged in the short term (known as acute effects), and the probability that the radiation will cause cancer in the long term (known as late effects).

There are billions of cells in the human body. If some cells are lost due to radiation damage, they are usually replaced by new cells. This is the case for patients receiving radiation from diagnostic procedures, which deliver such low doses of radiation that patients typically don’t experience short- or long-term effects. The average radiation dose a person in the US receives from natural sources in the environment is about 3 milliSieverts (mSv) per year, with a range of 1 to 20 mSv. (The millisievert, or mSv, is a commonly used unit of radiation dose.) Simple diagnostic x-ray procedures deliver doses less than 1 mSv for each procedure. More complex procedures such as x-ray computed tomography (CT) scans may deliver more dose to the imaged area, from 1 to 10 mSv, depending on the exam being performed. Diagnostic imaging is considered safe because the radiation doses delivered are similar to natural background levels of radiation, which have not been shown to cause short-term harm.

As the amount of radiation delivered to a patient increases, more cells are destroyed. At relatively high radiation dose levels, the damage and loss of normal cells has an observable effect. For example, during a daily radiation therapy treatment with a medical linear accelerator, radiation passes through the patient’s skin and penetrates their body to kill the targeted cancer. Total radiation dose to the skin can be around 3,000 mSv over the entire course of radiation therapy and the patient may experience a temporary skin reaction similar to a sunburn.

Exposure to radiation—whether from the natural environment, a person’s job, or medical procedures—may increase the risk of developing cancer in the long term. The question is by how much.

Most healthy cells are able to repair themselves after receiving small doses of radiation. Even if a cell’s repair isn’t perfect, it is unlikely to have any long-term impact. However, there is always a small chance, even at low levels of radiation exposure, that a surviving, damaged cell may eventually reproduce in an uncontrolled way. This can result in cancer.

Based on studies of populations exposed to very high levels of radiation, radiation-induced cancers can appear in a person years after exposure. For most patients with cancer, the immediate benefits from radiation therapy outweigh the small chance of developing a new cancer in the future. However, data does show that radiation therapy increases the risk for developing a second cancer during the patient’s lifetime. After about seven years, there is a slight increase in bone marrow and blood cancers, and after about twenty years there may be a small increase in solid tumors.

To put the risk in perspective, patients undergoing a diagnostic procedure receive the equivalent of about 1 mSv to their whole body. (Even though only part of the body may receive radiation, the dose received is commonly converted to a whole-body equivalent dose for the purpose of performing cancer risk calculations.) The natural cancer death rate in the U.S. is about 20% of the population. This means that out of every 100,000 people, 20,000 will eventually die of cancer. If 100,000 people each received 1 mSv from a diagnostic medical procedure, models predict 5 additional cancer deaths at some time long after that exposure. That means the risk of developing cancer would increase by 0.025% (20,005 deaths instead of 20,000). The lifetime fatal cancer risk increase from diagnostic radiation procedures is very low for an individual patient, while the medical benefits are immense. Overall, diagnostic imaging can be considered safe.

Although radiation treatments deliver much higher doses than diagnostic imaging procedures, those high doses are focused at the sites of disease, and the dose delivery is spread out over time to give healthy tissues time to repair themselves. The dose needed to destroy cancer cells is typically about 50,000 mSv, roughly ten thousand times higher than in diagnostic procedures. However, the risk for developing a fatal cancer from radiation therapy isn’t as high as this large dose might suggest because it is mostly targeted at cancerous cells.

The purpose of therapeutic radiation is to kill cancer cells that are an immediate threat. In the course of delivering that treatment, the radiation will pass through the body and deliver some dose to normal cells. This radiation dose to normal cells can introduce a risk for developing another cancer later in the patient’s lifetime. However, this risk is usually very low because only a small fraction of the normal tissues receive any radiation, and the dose is generally much less than that received by the cancerous cells. Depending on the case, normal tissue averaged over the whole body of a patient receives about 1/150^th of 50,000 mSv, or about 330 mSv. This will produce a fatal cancer in about 1500 of 100,000 people (1.5%) long after treatment. In other words, 98.5% of radiation-therapy patients will not develop a radiation-induced cancer. Although there is a small risk associated with radiation therapy, the benefit of curing the current cancer far outweighs the risks. Medical physicists work hard to keep these risks as low as possible, ensuring that the benefits of treatment outweigh the risks.

• Acute effects – Side effects that may occur immediately after radiation exposure
• Cancer – A disease in which cells grow uncontrollably and can spread to other parts of the body
• Cells – The tiny building blocks that make up all living things, including our bodies
• Diagnostic procedure – A medical test that helps doctors determine what is happening inside the body
• Late effects – Health effects that may appear years after radiation exposure
• Medical physicist – A specialist who ensures that medical devices using radiation work safely and effectively
• mSv (millisieverts) – A unit to express how much radiation dose a person received
• Natural radiation – Background radiation that comes from the sun, earth, and space, and which everyone is exposed to
• Radiation – Energy that travels in waves or particles. X-rays are the most common type of radiation used in medical tests and treatments.
• Radiation oncologist – A medical doctor who treats cancer using high doses of radiation
• Radiation therapist/technologist – A professional who helps deliver radiation treatments to patients
• radiologist – A medical doctor who uses imaging devices, such as X-rays, to see inside the body
• Therapeutic radiation – Radiation used to kill harmful cells, such as cancer cells, in the body
• Tumor – A lump or mass formed by extra cells in the body, and which can be cancerous
• X-ray – A type of radiation often used in diagnostic imaging and radiation therapy