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
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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Is it possible or necessary to receive 9 weeks of radiation 7 days a week?

Hi Elma, we are not able to answer specific medical questions, but radiation therapy is generally given five days a week. This gives normal, healthy cells a chance to recover from the radiation. If you’d like to consult with one of our radiation oncologists, you can call 800-525-2225 or go to for more information on making an appointment. Thank you for your comment.

My boyfriend recently had radiation on his thyroid. Afree 24 hours we slept in the same bed, sheets changed since first 24 hours. I've had a rash on my skin now for 4 days solely in one area. Can that be in any way related or is it not likely. (I am immunocompromised and have had a form of cancer before, so I'm just slightly worried.)

Dear Kasey, we are sorry to hear about your boyfriend’s diagnosis. For people who receive receiving radioactive iodine therapy for thyroid cancer, radioactive substances can be emitted through body fluids such as saliva, urine, and sweat for several days following this therapy. 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.

If he received external-beam therapy, it does not make a person radioactive in any way. The therapy only affects the patient’s cells for the very short time that they are receiving treatment. A person who has received external-beam radiation is unable to contaminate or transfer that radiation to any other person.

You can learn more about radiation safety here:…

We are unable to tell you if your rash or other symptoms are related to your boyfriend’s treatment. We recommend that you follow up with your physician to discuss your concerns. Thank you for reaching out to us.

My husband had 72 Cesium seeds implanted 4 weeks ago. Can you say more about the safety of intercourse? I'm confused if that's OK when 'spooning' is not recommended. We're both in our early 50s, married for 30 years.

Dear Michelle, it’s best to discuss your concerns with your husband’s oncologist. He or she is best equipped to answer questions about the particular type of seeds used and the safety of sexual intercourse and/or spooning. Thank you for reaching out to us.

Hi My Husband is having radiotharpy for Cancer of the neck,he has to have 33 treatments monday to friday, we sleep i the same bed , and ow I seam to have a cold all the time flu like , my Husband the same ,, should we be in separate beds ,

Dear Mary, we recommend you discuss your concerns with your husband’s healthcare team. Thank you for your comment.

At my job there's someone taking radiation pills twice per week for several months(they go in to the hospital to take them, and have to stay there for a few hours to make sure they don't react to the pill). Do I need to be concerned? Do I need to stay so many feet away from him? Also, when he leaves an area does radiation linger, or does it immediately go away? Me and my husband may try to get pregnant soon, and I want to take appropriate precautions.

Natalie, thank you for reaching out. We consulted with Jean St. Germain, MSK radiation safety officer, who responds:

This question is very difficult to answer without further information. There are certain pharmaceuticals administered as capsules; however, these are usually one-time administrations. HIPPA regulations limit the information you may be able to obtain. First, you can ask your co-worker directly and explain your concerns. If you know the name of the physician involved, you can try to contact him/her to obtain pertinent information. Again, HIPPA regulations may limit access to patient information.

Is IMRT used to treat nodules in the lung which are secondary to thyroid cancer?

Your article says, "Although it has been a widely used treatment for decades, confusion and misunderstandings about the safety of radiation treatment persist. " It fails to explain that radiation used to be more dangerous, with a greater chance of serious long-term health consequences. The problem in the old days was that doctors were insufficiently aware of how bad those dangers were, and the radiation was given in high doses to a wide area. I am glad that radiation is more targeted now. Too late for me, though (breast cancer, heart and lung damage).

Dear Elizabeth, we’re sorry to hear that you experienced side effects from the treatment that you received. Thank you for sharing your story, and best wishes to you.

I had radiation spheres released into my liver. I was told to sleep in separate bed. My husband is almost 68 years old. What is the risk of this?

We recommend that you discuss this with your doctor. Thank you for your comment.

My boyfriend was diagnosed with neck cancer mid June of this year. He has had twenty treatments but a few problems arising has kept him from getting them continuous through 7 wks, 5 days a wk. He is receiving the external-beam radiation. One of the doctors said it's unlikely that this treatment alone will cure his cancer. They say he's too weak for chemotherapy in addition to the radiation. Could you give me some insight on this? Thanks.

Dear Patricia, we’re very sorry to hear that your boyfriend is going through this. We are not able to make treatment recommendations on our blog, but if he would like to come to MSK for a consultation to learn about various options for therapy, he can call 800-525-2225 or go to for more information. Thank you for your comment, and best wishes to both of you.

My father just finished 25 treatments of radiation. His next step is either seed implant radiation or cyber knife. He is also getting hormone shots once every four months. With seed implant radiation we understand infants should not be on my father’s after the procedure. We also heard the children under the age of 18 should not be within three feet of my father... we are not clear on how long my father should be away from children under the age of 18. Is it for one month? Two months? Six months? Etc. what is the length of research completed on these results?

Dear Linda, we’re sorry to hear that your father is going through treatments for cancer. We recommend that you discuss your concerns with his medical team. Thank you for your comment, and best wishes to you and your family.

I had 35 radiation treatments to my tongue and neck , ct scan, 2 pet scans in 2017. I currently work as a dental assistant and take X-rays with a hand held portable unit while wearing a lead apron and thyroid collar. My question is am I exposing myself to extra life threatening radiation exposure.

Dear Billie, we recommend you discuss this with your employer or consult the OSHA standards for administering X-rays, to ensure that your procedures are compliant with the safety guidelines.

Thank you for your comment, and best wishes to you.

My husband had radioactive seeds implanted for prostate cancer treatment. He was told to use only bathroom in our house. With grandchildren expected to visit soon, I need to know how to clean the bathroom he uses so others are not effected.

We recommend that you discuss this with your husband’s healthcare team. Thank you for your comment, and best wishes to you both.

I Had 4 brain ct scans in 3 years from age 30 to 33 .im female . Is this high risk radiation now in developing cancer ?
Thank you ❤

Dear Britt, we recommend that you discuss your concerns with your doctor. Thank you for your comment, and best wishes to you.

My husband is considering brachytherapy treatment of prostate cancer. We have an old cat who loves nothing more that lying on top of my husband when he's in bed. We're wondering if a lead vest or lead apron might protect our cat so they can continue to cuddle. Please advise.

Dear Susan, we recommend that you discuss this with your husband’s doctor. He or she will be able to give you more information about this, depending on the type of seeds that will be used. Thank you for your comment and best wishes to you, your husband, and your cat.

I am a tutor about to receive brachytherapy for prostate cancer. About half my students are under the age of 13, and I normally sit next to them to see the questions they are answering and the techniques they use to get their answers. My students get 1 - 2 hourlong sessions per week. My doctor says I should not come within 6 feet of a child for 2 months after insertion of the seeds, though there is less risk to a child beside me than one in front of me. Is there some way I can cover my lap (for example with the item I get for dental x-rays) that might make me safe after one month instead of two?

Dear Ben, thank you very much for your important question.

We consulted with one of our brachytherapy experts who explained that radiation safety precautions depend a lot upon the particular type of seed that is used for the procedure. There are generally two types of seeds which are commonly used for brachytherapy and they include iodine 125 and palladium–103. Iodine–125 has a half-life of 60 days so that would mean that after 10 months the activity is basically out of the person’s body and come no longer be detectable. For palladium–103 seeds the half-life is only 17 days so the activity of the implant and its life only lasts for about 10 weeks. With extensive measurements we have done at MSK we have generally recommended to patients that with palladium seed implants the exposure externally is generally minimal and no radiation precautions are necessary. With iodine seed implants we usually recommend that for 10 months a distance is placed approximately the size/distance of a bowling ball from the lap of the individual who had the implant. In these situations a lead apron as is used by dentists in their office for x-rays would be more than adequate to protect anyone during those number of months where the seed implant could be active if someone is sitting for prolonged periods of times near students. Thank you for your comment, and best wishes to you.

My husband's coworker is in the hospital and they did a radiation test on him today, we didnt know that we couldnt take our 3 1/2 yr. Old daughter in there, we were in there for about 5-10 minutes, she gave him a hug and was by him talking to him, will anything happen to her. Plz help answer my question, thank you.

Dear Melanie, we recommend that you talk to your friend’s doctor about what type of agent was used in his test and whether it poses any risks to others. Thank you for your comment.

My father had Brachytherapy (i believe iodine type) about 4 weeks ago. We are going to visit for Christmas and I have two children - a 5 month old and a 2 year old. I have read online the various recommendations about 3 to 6 feet distances. Some advice says for the first month limit visits to 1 hour. Seeing that we are approximately 1 month out from his procedure, can we visit on Christmas day and Boxing Day for several 2 hour periods each day if we keep the kids more than 6 feet away from him? I'd like to visit and keep Xmas as normal as possible, but also err on the side of caution where needed.
Thanks so much.

Dear Simon, this is something that your father should discuss with his doctor. Thank you for your comment and happy holidays to your family.

My father was a private contract engineer for nuclear testing on Enewetak in 1957-8 over a 6 month period.10 yrs later at 48 he had a massive MI and died. My mother got pancreatic cancer 38 yrs later. I see there can be damage to the cardiovascular system from radiation and that it can be passed on via body fluids. Where, medically, can my brother and I follow up on our health care needs. My father was both in Project Red Wing and WIGWAM. Also who is studying this situation? Thank you for your assistance. Karen Golinveaux RN

Dear Karen, we recommend that you discuss this with your doctor. Thank you for your comment and best wishes to you and your family.

I had Stage 1 Figo Grade 111B endometrial cancer and a total hysterectomy. However, the tumor dropped down into the "vaginal wall" and I was told to have EBT and Brachytherapy. I refused the EBT because of the side effects. I was told that it was "superficial" in the vaginal wall. No one has told me whether or not this may be just as protective against a recurrence. I asked the Radiologist and I don't get a direct answer of any kind. DOESN'T ANYONE KNOW?...She said I was "unique" because in her 30 years of being a Radiologist she never saw anyone with Stage 1 (which is curable with just surgery) but then having a drop down in t he vaginal wall and it being Figo Grade 111B. You can only imagine how "upsetting" that is to hear and I feel like an "alien" because no one else seems to have this situation?...Is this true? And I have researched all over the Internet and find very little information about what I have....I am a very active person and truly cannot deal with "side effects" from being radiated all over the pelvis/abdomen. PLEASE ADVISE....THANK YOU!

Dear Gayle, we’re sorry to hear about what you’ve been through. If you’re interested in consulting with an expert at MSK you can make an appointment on online or call 800-525-2225 Monday through Friday during regular business hours. Thank you for your comment and best wishes to you.

I had two "seeds" implanted and have received 4 treatments for a pre-cancerous, bacterial tumor. It is not having the desired effects and due to negative reactions they have decided to remove the "seeds". Just found out my boss is pregnant and have a grandson 10 months old I want to visit for his birthday. How long will I be "radioacative" or need to stay away from both the grandson and my pregnant boss??

Dear Marge,

Thank you for your question. We recommend you discuss this with your care team or doctor, who will be able to give you more specific information.

You also can learn more about radioactive seeds here: