Answers to Common Questions about Radiation Safety

Two doctors looking at a patient

Radiation oncologist Melissa Zinovoy (right) and chief radiation therapist Beeban Natt with a patient at MSK Westchester.

Radiation treatment is one of the most common and effective ways to destroy cancer cells and shrink tumors. At Memorial Sloan Kettering, approximately half of our adult cancer patients undergo radiation therapy as a primary treatment or as part of a broader approach that includes chemotherapy, surgery, or other therapies. For many cancers, radiation therapy may be all that is needed to treat the disease.

There are different ways to deliver radiation treatment. With external-beam radiation therapy, treatment is delivered from a machine outside the body. With internal radiation (brachytherapy), sealed sources of radioactivity are placed near or within the tumor. Less commonly, radiation treatment can also be given using liquid materials in capsules by mouth or infusion through a vein (systemic radiation).

Although radiation treatment has been widely used for decades, there still is confusion and misunderstandings about its safety. We asked MSK clinical physicist Lawrence Dauer and medical physicist Matthew Williamson to tell us about the concerns they hear most frequently from patients and their families — and the answers and reassurance they provide.

Will receiving external-beam radiation make me radioactive or able to expose others to radiation?

External-beam therapy, the most common type of radiation treatment, does not make a person radioactive in any way. It is applied most often in the form of x-rays by a linear accelerator. The therapy is designed to deliver precise amounts of energy to tumor cells while sparing healthy tissue. The radiation is present only when the linear accelerator is operating. When you receive external-beam radiation, you are unable to contaminate or transfer that radiation to any other person.

When you receive external-beam radiation, you are unable to contaminate or transfer that radiation to any other person.
Lawrence T. Dauer clinical physicist
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How can I be sure that the external-beam radiation machine isn’t damaging normal, healthy tissue in my body?

We have carefully developed methods for calibrating radiation beams to ensure they reach the areas they are intended to target. Even when nearby normal tissues receive small amounts of radiation, it is rare for long-term damage to occur. Our doctors and physicists also know how much radiation healthy tissue can receive without causing significant damage. They use this information to develop a patient-specific treatment. We often use special masks, molds, or casts of body parts to keep you completely still during treatment so that we can aim the radiation beams precisely to the area that needs to be treated.

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Is there any risk that internal radiation implants (brachytherapy) will leak or break free from where they are placed and move around my body?

With brachytherapy, we use a needle or a catheter to insert radioactive material contained within a sealed source such as a seed, pellet, wire, or capsule. As the radioactive material inside the implants decays naturally over time, it emits radiation that deposits energy to treat nearby cancer cells. This radioactivity travels only a certain distance beyond the implant. Within a few weeks or months, the implant no longer gives off any radiation. The implants are specially tested and sealed to ensure that the encapsulated radioactive material doesn’t leak, and we place them in such a way that it’s highly unlikely they will move. We give people specific precautions to minimize exposure to others from the implanted radioactive material.

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Should I limit contact with anyone while brachytherapy implants are inside my body?

Most of our safety concerns are related to being in physical contact with children for extended periods of time because their bodies are undergoing such rapid change and growth. Because we vary the radiation dose in each implant as well as the number of implants we insert based on your particular cancer, we provide you with specific advice about precautions to take when you’re in close contact with children.

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Do prostate seed implants put my sexual partner or the person I sleep next to at risk in any way?

Prostate seeds are sealed sources. You cannot contaminate another person by being in his or her physical vicinity, during sexual intercourse, or through any other form of intimate contact. Your doctor or a member of the radiation safety staff will discuss any special precautions you should take with sleep arrangements before you leave the hospital. For example, based on such factors as your age and the age of your partner, we may ask that for a short time you avoid embracing your partner from the back in the “spooning” position through the night.

Radiation Therapy for Cancer
Radiation therapy can destroy tumors and/or prevent them from returning. It can be used by itself as the only treatment or in combination with surgery, chemotherapy, or both. Learn more about the types of radiation therapy and how it's used at MSK.
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Do I pose a danger to others after receiving radioactive iodine therapy for thyroid cancer?

Radioactive iodine treatment involves swallowing a capsule or liquid form of radioactive iodine that all thyroid cells take up (absorb), destroying them. It’s effective because other healthy cells in the body don’t usually absorb the radioactive iodine.

For several days following this therapy, radioactive substances can be emitted through body fluids such as saliva, urine, and sweat. We send patients home with detailed instructions on how to care for themselves for the first few days — from limiting contact with young children and pets to using separate utensils and towels.

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I am having an imaging test using radioactive materials. Will I be radioactive after the test?

Doctors sometimes use small amounts of radioactive material to diagnose disease. This is called nuclear medicine. The radioactive substance is injected into your body, locating specific cells or tissues ― including cancer cells ― and binds to them. The radioactive material will stay in your body for several hours or days, depending on the type that is used. Eventually, the material decays and your body naturally flushes it out through urine, sweat, and other forms of biological elimination. We make sure the specifics are clear to you before the test, and we may also issue an information card explaining your treatment in case you are questioned by someone in airport security, for example. You can learn more about nuclear medicine approaches here.

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Editor’s note: This story was originally published in 2014 and was updated in 2020.


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no one ever told me when I had radiation 8 years ago that I could develop an Angiosarcoma...So it's a big surprise that I now have a full blown sarcoma.

Following Brachytherapy and beam radiation is there a limit to the amount of radiation to a particular site?
If further cancer develops in the bone area already treated can further radiation be used to quell or kill the cancer?
What is the outcome of too much radiation to a bone or soft tissue site?
Are there further options in such circumstances?
Thanks for your help.

Roger, thanks for reaching out! There are no specific regulatory limits on the amount of radiation to a particular site during treatment when that treatment has been deemed appropriate and justified by your doctor. Our doctors follows appropriateness criteria and accepted professional guidance, along with best procedures based on the latest research to deliver appropriate treatments. They always seek to target the most effective dose of radiation directly at the cancer, while minimizing radiation to the healthy parts of a patient’s body. Decisions about the best therapy and best technology are based on each individual case. Also, different tissues have a different sensitivity and response to various types of radiation. Each case is unique.

Unfortunately we can’t answer personal medical questions on our blog. But if you or someone you care for has had radiation to the bone and you are wondering about treatment options, we encourage you to consult with one of our specialists. Please call our Physician Referral Service at 800-525-2225.

Radiation caused damages to chromosomes.Will long term Radiotherapy treatment cause permanent chromosomal damages leading to gene mutation?

I too am interested in the damage to chromosomes leading to gene mutation.
Since radiation three years ago I have developed MDS. Is there a possible link?

Thank you for writing, Carol! Unfortunately we cannot answer personal medical questions on our blog. If you would like to make an appointment for a consultation with one of our specialists who can provide a personalized assessment of your treatment options, please call our Physician Referral Service at 800-525-2225.

It is stated above, "it is rare for long term damage to occur." Are the studies available to confirm this? i.e. breast radiation - 10 years later, lung or respiratory damage?

Lana, we sent your question to Beryl McCormick, Chief of our External Beam Radiotherapy Service, who responded that there have been several studies of the long-term effects of breast radiation. Two of the largest were reported in the New England Journal of Medicine in 2002
( and in the Lancet Oncology in 2005 ( She noted that this area has been studied with much longer follow-up than some of the newer chemotherapy regimens. Thank you for your comment.

Are there any allergic reactions caused by the radioactive material used during a CT scan or a PET scan such as Itching and a soft red rash?

Joe, radioactive materials are not used during regular CT scans, but they are used during PET scans and PET/CT scans. It’s possible to have an allergic reaction to the tracer. If you think you have had an allergic reaction, we recommend that you discuss this with your doctor. Thank you for your comment.

Are you allowed to go swimming after radiation treatment

Eileen, radiation treatment can cause sensitivity of the skin, so this is something you should discuss with your doctor. Thank you for your comment.

As a caregiver, what precautionary safety measures do i take when one of my clients start radiation treatments for 7 weeks, 5 days a week?

External-beam therapy does not make a person radioactive in any way. The therapy only affects your cells for the very short time that you are receiving treatment. A person who has received external-beam radiation is unable to contaminate or transfer that radiation to any other person. Thank you for your comment.

I have had a full hysterectomy and was classified as stage one. Soon I will be receiving brachytherapy to my vaginal cuff. How long is the possible risk of radiation exposure to my young grandchildren and others? I don't want to be treated as a leper but also don't want to harm others in even the slightest way.

I have been diagnosed with breast cancer, and have a choice between mastectomy and lumpectomy with radiation. I also have extensive psoriasis, which has been kept under control for several years with short daily UVB-narrow spectrum radiation treatments. Would I be able to continue those treatments if I have radiation therapy for the cancer? Thank you for your answer.

This is something you should discuss with your dermatologist and your radiation oncologist. Thank you for your comment.

My husband had brachy therapy may 2015. June2015 I developed a topical dermatitis on my hands which I only managed to clear by December. I have now developed shingles on my face. The only changes was hisbrachy treatment. I'd it possible that my immune system has weakened from sleeping inthe same bed

Linda, thank you for reaching out. We passed your question on to MSK expert Laurence Dauer, who responds:

Several studies have been performed that have shown that the exposure to any family members from brachytherapy patients are well below any recommended precaution limits. As such, it is not at all likely that your immune system was weakened from sleeping in the same bed. The potential dose rates are simply much to small to have any effect.

I will soon be having a course of radiation after lumpectomy for DCIS. I also have Hashimoto's Thyroiditis and have been warned to avoid X-rays as much as possible (airports,dental) due to risk of thyroid cancer. I've been told no shield will be used on my thyroid which concerns me. Thank you.

Dear Karen, we are sorry to hear about your diagnosis. We encourage you to discuss any questions or concerns you may have with your physician. Thank you for your comment.

My husband had a 200 milicure (don't know if I spelled it correctly) dose of radioactive iodine 13 days ago...we just had oral sex for the first time since the treatment...I swallowed the semen. Will I be in any danger?

Linda, we recommend you discuss with your husband’s healthcare team how long the radioactive iodine remains in the body after the treatment he had. Thank you for your comment.

I had a lumpectomy last week in January. I was advised to start radiation treatment 6-8 weeks after surgery. I have a family event coming up & would like to know if I postpone another 4 weeks do I put myself at an unnecessary risk? Please advise.

Thank you

Dear Marie, we are sorry to hear about your diagnosis. Unfortunately, we are not able to offer specific medical advice on our blog. Please follow up with your oncologist, who knows your full medical history and can provide a more informed recommendation for you. Thank you for reaching out to us.

Can a person that has stared radiation treatment in one city be transferred to another
The reason I ask is because my husband is like 2hours away and I can't get the equipment needed for home care of his trach

We recommend that you ask your husband’s healthcare team what other options may be available for his treatment. Thank you for your comment.

I understand that EBRT focuses on the tumor or tumor site thus reducing harm to nearby healthy tissue. But what if it is being used as a preventive: If there is no evidence of disease and it is being used in case a microscopic cancer cell remained behind after surgery, then it is zapping healthy tissue. Will that lead to long term side effects?

Dear Lorraine, we sent your inquiry to medical physicist and radiation safety expert Jean St. Germain and she responded:

“The goal of modern techniques such as Intensity Modulated Radiation Therapy [IMRT] or Image Guided Radiation Therapy [IGRT] is to maximize the dose to the tumor while sparing as much normal tissue as possible. Neither of these techniques are used as a preventative. There must be a disease process present to prescribe radiation therapy. That disease process is usually a cancer, although there may be the rare circumstance in which radiation therapy is used on a serious, but non-cancerous, disease process such as an aterio-venous malformation [AVM]. The potential for cancer cells to escape during surgery or radiation treatment depends on the type of tumor, its location, and the profession’s overall experience with the type of disease involved. Typically, chemotherapy, a systemic treatment, may be used in these cases.”

We hope this information is helpful. Thank you for reaching out to us.

Yesterday I took 9 small dose pills of 1-123 iodine radiation for a full body scan last month I had almost all of my thyroid removed for papillary cancer I have a 1/4 of my thyroid left cause of the location of a mass and the one nerve left for my voice box still attached with no damage the doctor wants to see if we can kill the rest of the cancer with radiation but the pet scan showed up 2 spots in my lungs so that's why I got a full body scan today but curious how long I have to stay away from my very young great nieces and nephews being I'm a important part of their lives!

Frank, this is something you should discuss with your doctors. Thank you for your comment.

My 20 year old daughter received radioactive iodine treatment for her thyroid cancer (small tumor) on Tursday. My 16 year old son wants to go see her for a little while which I'm not sure is a good idea just yet and haven't decided to let him do so. If he does what is the risk to him and is there a risk that he can pass along any radioactive material to his younger brother and sister?

Eric, we sent your question to Jean St. Germain, who replied, “Radioiodine (I-131) is used for treatment of thyroid tumors because the thyroid concentrates the iodine. Approximately 50% of the administered dose is excreted within 24 hours, primarily in urine, but also in sweat and saliva with a small amount in feces. The biological excretion continues in smaller amounts, and eventually, all iodine remaining in the body is concentrated in the thyroid itself. After approximately 72 hours, there is little biological elimination. As long as your son does not contact bodily fluids, the chief problem would be exposure from the iodine in her thyroid. It would usually be recommended that visitors remain at a distance of approximately 1 meter (about 3 ft.) for a period of about 1 week. Since these statements are in general, you may wish to consult with the authorized nuclear medicine physician who administered the therapy.” Thank you for your comment.

Just went threw 42 radiation and 6 chemo had tonsils uvula esophagus and lymphoids cancer feeding tube and port now thyroid fried anyone have input

In regard to lung cancer resulting from radiation therapy treatment for breast cancer, I read in an article from cancergrace stating that data from the United States and Sweden indicates that patients treated before the mid 1980’s were noted to have approximately a 0.5% increase in the risk of developing lung cancer – almost all secondary lung cancers appear to be in smokers. However, among patients treated in the last 30 years, this increased risk of lung cancer has disappeared. In your experience, would you say that this is true?

Mamie, thank you for your question. We consulted with MSK radiation oncologists, who state that “Techniques have improved dramatically since the 1980’s, but it will take at least 15 years after treatment refinements have been routine to detect the impact on long term consequences of radiation, of which secondary cancers are one.”

I have heard that after having radiation seeds to treat cancer the affected area can eventually adhere to other nearby organs, thus making those organs inoperable. Can surgery still be done on other parts of the body not affected by the seeds?

Dear Ralph, we forwarded your inquiry to Dr. Michael Zelefsky, Chief of MSK’s Brachytherapy Service. He responded:

“With modern day radiation techniques, the likelihood that radiation seeds cause scarring to the effect that the prostate adheres to other organs would be extremely unusual. Radiation of course can cause some scarring on the sphincter muscles making subsequent prostate surgery riskier for incontinence of urine. After prostate radiation, surgery can still be done on other parts of the body in general without difficulty.”

We hope this is helpful. Thank you for reaching out to us.

Had small stage 1 breast cancer in left breast removed 11/2015. Clean margins, sentinel node negative. Tumor analysis showed HER2+, ER+, PR+
Treatment: 12 weeks of Taxol + Herceptin, followed by 1 year Herceptin every 3 weeks for the HER2+. Because I had lumpectory oncologist suggested radiation to left breast after Taxol completed. I asked for research on the value of this - I am 82 yrs. old. He found conflicting reports. What is your opinion?

My boyfriend had the radiation therapy for hyperthyroid a week ago, then i accidentally used his utensils. Wondering what may happen to me or to anybody used it?

My boyfriend had an radiation therapy for hyperthyrodism a week ago and i accidentally used her utensils, was wondering what may happen after using it?

Angela, we recommend you discuss this with your boyfriend’s healthcare team. Thank you for your comment.

what is the normal time frame for a patient to recover from radiation treatments to the throat .. also she has developed ulcers in her mouth from the radiation .. is this normal...

Hi John, we recommend that you discuss this with the patient’s healthcare team. Thank you for your comment.

My friend had radiation seeds put in on Tuesday to her lungs for cancer.. I was in pretty close contact to her and I want to help her but I am scared.. is it ok?

Dear Chrissy, according to this Q&A: “Most of our safety concerns [regarding brachytherapy] are related to being in physical contact with children for extended periods of time, since their bodies are undergoing such rapid change and growth and are therefore more vulnerable to abnormal cell changes. Because we vary the radiation dose in each implant as well as the number of implants we insert based on your particular cancer, we provide you with specific advice about precautions to take when you’re in close contact with children.”

We recommend that your friend discuss your particular concerns with her physician. Thank you for reaching out to us.

Someone I work with had a PET scan yesterday and is now back at work the next day . Does this affect me in any way ? Also the 7 year old children she is near ?