Radiation Therapy: How It Works, Types & Side Effects

What Is Radiation Therapy and How Does It Work?

Radiation therapy uses high-energy ionizing radiation to damage the DNA of cancer cells, preventing them from dividing and growing. The radiation destroys cancer cells by causing breaks in their genetic material. While healthy cells are also affected, they are generally better able to repair this damage than cancer cells, which is why treatment is typically given in multiple sessions.

Radiation therapy, also known as radiotherapy, has been used to treat cancer for over a century and remains one of the cornerstones of modern oncology. The treatment works on a fundamental principle of cell biology: cells that are actively dividing are more susceptible to radiation damage. Since cancer cells divide more rapidly and less efficiently repair DNA damage compared to normal cells, they are preferentially destroyed by radiation.

The ionizing radiation used in cancer treatment is powerful enough to strip electrons from atoms in the cells it passes through. When this occurs in the DNA of a cancer cell, it creates breaks in the genetic code that prevent the cell from successfully dividing. Over time, these damaged cells die and are cleared away by the body's natural processes. This is why tumors typically shrink gradually over weeks or months following radiation treatment rather than immediately.

Modern radiation therapy has evolved dramatically from its early days. Today's treatments use sophisticated imaging technology, computer-aided planning, and precision delivery systems to maximize the dose to the tumor while minimizing exposure to surrounding healthy tissues. This therapeutic ratio - the balance between killing cancer cells and preserving normal tissue - is the key challenge that radiation oncologists work to optimize for each patient.

Curative vs. Palliative Radiation

Radiation therapy can serve different purposes depending on the clinical situation. Curative (or radical) radiation therapy aims to eliminate the cancer entirely and is used when there is a reasonable chance of long-term disease control. This approach typically involves higher total doses delivered over several weeks, as the goal is complete tumor eradication.

Palliative radiation therapy, in contrast, focuses on relieving symptoms and improving quality of life when cure is not the primary goal. This might include treating painful bone metastases, shrinking tumors that are causing breathing difficulties, or controlling bleeding from a tumor. Palliative treatments are usually shorter, involving fewer sessions and lower total doses, as the aim is symptom relief rather than tumor elimination.

Radiation in Combination with Other Treatments

Radiation therapy is frequently used as part of a multimodal treatment approach. When combined with surgery, radiation may be given before the operation (neoadjuvant) to shrink the tumor and make it easier to remove, or after surgery (adjuvant) to destroy any remaining microscopic cancer cells. The timing and sequencing of these treatments is carefully planned by a multidisciplinary team of specialists.

Chemoradiation combines radiation therapy with chemotherapy drugs, which can enhance the effectiveness of radiation by making cancer cells more sensitive to its effects. This approach is commonly used for cancers of the head and neck, lung, esophagus, and cervix. While more intensive, chemoradiation has been shown to improve outcomes for many cancer types compared to either treatment alone.

What Are the Different Types of Radiation Therapy?

The two main categories of radiation therapy are external beam radiation (delivered from outside the body) and internal radiation or brachytherapy (placed directly inside or near the tumor). External beam therapy is more common and includes advanced techniques like IMRT, SBRT, and proton therapy that allow precise tumor targeting.

Understanding the different types of radiation therapy helps patients know what to expect from their treatment. The choice of radiation type depends on several factors, including the cancer type and location, tumor size, overall treatment goals, and the patient's general health. Your radiation oncologist will recommend the most appropriate approach for your specific situation.

External Beam Radiation Therapy (EBRT)

External beam radiation therapy is the most common form of radiation treatment, used in approximately 80% of all radiation therapy cases. During EBRT, a machine called a linear accelerator (or linac) generates high-energy X-rays or photon beams that are directed at the tumor from outside the body. The patient lies on a treatment table while the machine rotates around them, delivering radiation from multiple angles.

The treatment itself typically takes only a few minutes of actual radiation delivery, though the entire appointment may last 15-30 minutes due to positioning and setup time. Most EBRT treatment courses involve daily sessions (Monday through Friday) for 2-7 weeks, depending on the cancer type and treatment intent. This fractionated approach allows healthy tissues to recover between sessions while accumulating damage in the tumor.

Several advanced EBRT techniques have been developed to improve targeting accuracy:

• Three-Dimensional Conformal Radiation Therapy (3D-CRT): Uses CT imaging to create a 3D model of the tumor, allowing radiation beams to be shaped to match the tumor's contours
• Intensity-Modulated Radiation Therapy (IMRT): An advanced form of 3D-CRT that varies the intensity of radiation across the treatment field, enabling even more precise dose distribution
• Image-Guided Radiation Therapy (IGRT): Uses real-time imaging during treatment to account for tumor movement and ensure accurate targeting
• Stereotactic Body Radiation Therapy (SBRT): Delivers very high doses of radiation in fewer sessions (typically 3-5) with extreme precision
• Stereotactic Radiosurgery (SRS): Similar to SBRT but specifically for brain tumors, often completed in a single session

Proton Therapy

Proton therapy is a specialized form of external beam radiation that uses protons instead of X-rays. The key advantage of protons is their unique physical properties - they can be precisely controlled to deliver most of their energy at a specific depth (the Bragg peak) and deposit very little dose beyond the tumor. This makes proton therapy particularly valuable for tumors located near critical structures like the brain, spine, or heart.

Proton therapy is especially beneficial for pediatric cancers, as reducing radiation exposure to developing tissues can minimize long-term side effects and reduce the risk of secondary cancers later in life. It is also used for certain adult cancers including some brain tumors, prostate cancer, and tumors at the base of the skull or near the spine.

Brachytherapy (Internal Radiation)

Brachytherapy involves placing radioactive sources directly inside or next to the tumor. This allows a very high dose of radiation to be delivered to the cancer while largely sparing surrounding healthy tissues. The radioactive sources may be placed temporarily (removed after treatment) or permanently (left in place to gradually lose their radioactivity over time).

There are several forms of brachytherapy:

• Interstitial brachytherapy: Radioactive seeds or sources are placed directly into the tumor tissue, commonly used for prostate cancer
• Intracavitary brachytherapy: Sources are placed in a body cavity adjacent to the tumor, frequently used for gynecological cancers
• High-dose-rate (HDR) brachytherapy: Delivers treatment over minutes in an outpatient setting; sources are removed after each session
• Low-dose-rate (LDR) brachytherapy: Involves continuous exposure over hours or days, or permanent seed implants

Before brachytherapy, you may need a minor surgical procedure to place thin tubes (catheters) or applicators in the treatment area. These remain in place during treatment and allow the radioactive sources to be inserted and removed. For permanent implants like prostate seed brachytherapy, tiny radioactive seeds are placed directly in the prostate and remain there permanently, though they become inactive over several months.

Systemic Radiation Therapy

Some radiation treatments are delivered systemically through injections or oral medications containing radioactive substances. These radiopharmaceuticals travel through the bloodstream and target cancer cells throughout the body. Examples include radioactive iodine for thyroid cancer and radium-223 for prostate cancer that has spread to bones.

How Do You Prepare for Radiation Therapy?

Preparing for radiation therapy involves a simulation session where imaging scans map your tumor's exact location, followed by treatment planning that typically takes about one week. You may receive small tattoo marks on your skin for positioning, and custom immobilization devices may be created to help you stay still during treatment.

The preparation phase is crucial for radiation therapy success. Unlike some cancer treatments that can begin immediately, radiation therapy requires careful planning to ensure the treatment is delivered precisely where it is needed while protecting healthy tissues. This planning process typically takes one to two weeks before your first actual treatment session.

Initial Consultation

Your radiation therapy journey begins with a consultation with a radiation oncologist, a physician who specializes in using radiation to treat cancer. During this appointment, your doctor will review your medical history, examine you, and discuss imaging studies and pathology reports. They will explain why radiation therapy is recommended for your situation, describe what to expect during treatment, and answer your questions.

This is also an opportunity to discuss your treatment goals and any concerns you may have. You might want to bring a family member or friend to help remember the information discussed, and consider writing down questions beforehand. Topics to discuss might include the expected number of treatments, potential side effects, impact on daily activities, and long-term outlook.

Simulation Appointment

The simulation is a planning session that typically lasts one to two hours. You will lie on a special table in the same position you will be in during treatment, and imaging scans (usually CT, sometimes with MRI or PET) will be performed to create a detailed map of your tumor and surrounding anatomy. This simulation allows the radiation team to determine the exact area to be treated.

During simulation, custom immobilization devices may be created to help you maintain the same position for each treatment session. Depending on the treatment area, these might include:

• Head and neck treatments: A custom plastic mesh mask that fits snugly over your face and secures to the table
• Chest or abdomen: Custom foam molds or vacuum cushions that conform to your body shape
• Breast treatments: Arm boards or positioning devices to keep the arm raised
• Pelvis or extremities: Leg immobilizers or specialized positioning systems

Small permanent tattoo dots (smaller than a freckle) or temporary ink marks may be placed on your skin to guide positioning for each treatment. These reference points ensure that the radiation beams are aimed at exactly the same location every time. If you receive temporary marks, you will be instructed not to wash them off; avoid scrubbing the marked area and skip deodorant or lotions on treatment days if treating the chest area.

Treatment Planning

After simulation, your medical team uses sophisticated computer software to design your treatment plan. This process involves the radiation oncologist, medical physicists who ensure accurate dose calculations, and dosimetrists who optimize beam arrangements. The goal is to deliver the prescribed dose to the tumor while minimizing exposure to healthy structures.

The planning team reviews detailed images from your simulation to outline the tumor target and identify nearby organs that need protection. They then calculate how to shape and aim the radiation beams to achieve the best possible dose distribution. For complex cases, this planning process may take several days to a week.

Pre-Treatment Instructions

Your healthcare team will provide specific instructions to follow before and during treatment. General recommendations may include:

• Quit smoking: Smoking reduces oxygen in tissues, making radiation less effective and increasing side effects
• Maintain good nutrition: Your body needs energy and nutrients to heal - a balanced diet supports recovery
• Stay hydrated: Drink plenty of fluids unless otherwise instructed
• Review your medications: Some medications may need to be adjusted during treatment
• Skin care: Keep the treatment area clean and dry; avoid irritants
• Plan for transportation: Arrange rides to daily appointments, especially if you may feel fatigued

What Happens During a Radiation Therapy Session?

Each radiation therapy session typically lasts 10-20 minutes, with the actual radiation delivery taking only 2-5 minutes. You will lie on a treatment table while technologists position you precisely, then leave the room during radiation delivery. The treatment is painless - you cannot see, hear, or feel the radiation beams.

Understanding what happens during treatment can help reduce anxiety and prepare you for the experience. While the treatment room contains sophisticated equipment that may look intimidating at first, most patients quickly become comfortable with the routine.

Arriving for Treatment

When you arrive at the radiation therapy department, you will check in at the reception area and wait briefly until the treatment team is ready for you. Depending on the treatment area, you may need to change into a hospital gown. Remove jewelry, watches, and other metal objects from the treatment area, and avoid applying lotions, deodorants, or powders to the skin being treated on treatment days.

Most treatment facilities run on a tight schedule, with appointments booked at specific times throughout the day. You will typically have the same appointment time each day, which helps establish a routine. If you are running late or need to reschedule, contact the department as soon as possible.

The Treatment Room

The treatment room contains the linear accelerator, a large machine that generates and delivers the radiation beams. The machine has a treatment table (sometimes called a couch) where you will lie, and a gantry that can rotate around you to deliver radiation from different angles. Many modern machines also include imaging equipment to verify your position before each treatment.

The room may seem cold due to the temperature requirements for the equipment. Feel free to ask for a blanket if you are uncomfortable. There is typically a camera and intercom system so the therapists can see and communicate with you at all times during treatment.

Positioning and Verification

Radiation therapists (also called radiotherapy technologists) will help you onto the treatment table and position you using the immobilization devices and skin marks from your simulation. They will make precise adjustments to ensure you are in exactly the right position, which may involve using lasers mounted on the walls for alignment.

Before your first treatment and periodically throughout your course, imaging verification will be performed to confirm accurate positioning. This might involve X-rays, CT scans, or other imaging taken on the treatment machine. If any adjustments are needed, the therapists will make small corrections to your position or the machine settings.

During the Treatment

Once you are properly positioned, the therapists will leave the room and go to an adjacent control area. This is necessary because even small amounts of daily radiation exposure would be harmful to the staff over time. You are never alone, however - the therapists monitor you constantly through cameras and can hear you through the intercom.

The machine may make clicking, buzzing, or whirring sounds as it operates and rotates around you, but the radiation itself is completely invisible and cannot be felt. You should breathe normally and remain as still as possible during treatment. For some treatments, you may be asked to hold your breath briefly while the radiation is delivered, as this helps protect healthy tissues like the heart during breast cancer treatment.

The actual radiation delivery typically takes only 2-5 minutes, though the total time in the treatment room is usually 10-20 minutes including setup. If you feel uncomfortable or need to stop for any reason, simply speak or raise your hand - the therapists will pause treatment and come to assist you.

Children Receiving Radiation Therapy

Young children who cannot lie still during treatment may receive sedation or general anesthesia for each session. This ensures they remain motionless for accurate treatment delivery. If your child needs anesthesia, additional time is required for preparation and recovery, and specific fasting instructions must be followed before each appointment.

Parents can typically stay with their child until the anesthesia takes effect and are called back as soon as treatment is complete and the child is waking up. The pediatric oncology team will provide detailed guidance and support throughout the treatment process.

What Are the Side Effects of Radiation Therapy?

Common radiation therapy side effects include fatigue (affecting up to 80% of patients), skin changes in the treated area, and localized effects depending on the body part being treated. Most early side effects resolve within weeks after treatment ends, though some late effects may develop months or years later.

While radiation therapy is carefully planned to minimize effects on healthy tissues, some degree of side effects is expected. The type and severity of side effects depend on several factors, including the area being treated, the total dose of radiation, whether you are also receiving chemotherapy, and your overall health. Understanding potential side effects helps you prepare and know when to seek help.

Early (Acute) Side Effects

Early side effects typically begin after two to three weeks of treatment and may continue for a few weeks after treatment ends. These are generally caused by damage to rapidly dividing cells in the treatment area and resolve as these tissues heal.

Fatigue is the most common side effect of radiation therapy, affecting the majority of patients to some degree. This is not ordinary tiredness - radiation-related fatigue can feel overwhelming and is not fully relieved by rest. The fatigue often builds gradually over the course of treatment and may peak one to two weeks after completing therapy before slowly improving.

Managing fatigue involves balancing rest with light activity. While it may seem counterintuitive, moderate exercise such as short walks can actually help improve energy levels. Taking shorter, more frequent rest periods is generally more helpful than one long nap. Most patients find their fatigue improves significantly within a month or two after finishing treatment.

Skin changes in the treatment area are also very common. The skin may become red (like a sunburn), dry, itchy, or tender. In some cases, particularly in skin folds or high-dose areas, the skin may peel or develop moist patches. These changes are usually worst one to two weeks after treatment ends and then gradually heal.

Skin care during radiation includes:

• Washing gently with mild, unscented soap and lukewarm water
• Patting the area dry rather than rubbing
• Avoiding irritants such as perfumes, deodorants (unless approved), or adhesive bandages on treated skin
• Wearing loose, soft clothing over the treatment area
• Protecting the skin from sun exposure during and after treatment
• Using moisturizers as recommended by your care team

Site-Specific Side Effects

Many side effects are specific to the body region being treated:

Head and neck radiation may cause dry mouth, difficulty swallowing, mouth sores, taste changes, and hair loss in the treated area. Dental problems can develop if the salivary glands are affected, so dental evaluation before treatment and good oral hygiene during treatment are important.

Chest radiation may cause difficulty swallowing if the esophagus is in the treatment area, or cough and shortness of breath if lung tissue is affected. Breast radiation can cause skin changes and temporary breast swelling.

Abdominal and pelvic radiation commonly causes digestive symptoms including nausea, diarrhea, cramping, and increased urinary frequency or urgency. These symptoms are usually manageable with dietary modifications and medications.

Brain radiation may cause headaches, nausea, and fatigue. Hair loss occurs in the treated area, and some patients experience temporary cognitive changes.

Late (Chronic) Side Effects

Some side effects may not appear until months or even years after treatment. These late effects result from permanent changes to the treated tissues and are generally less common than acute effects, though they tend to be longer-lasting.

Fibrosis (scarring) can develop in treated tissues, causing them to become firm or less flexible. This may affect skin, muscles, or internal organs depending on the treatment area. Lymphedema (swelling due to lymphatic damage) can occur after radiation to areas with lymph nodes.

Effects on fertility may occur if reproductive organs are in or near the treatment field. Radiation to the ovaries or testes can reduce fertility or cause premature menopause in women. If fertility preservation is a concern, discuss options with your oncologist before starting treatment.

Secondary cancers are a rare but potential long-term risk. While radiation can cause new cancers years after treatment, the risk is very small compared to the benefit of treating the current cancer. Modern treatment techniques have reduced this risk further.

What Is Recovery Like After Radiation Therapy?

Most acute side effects improve within 2-6 weeks after completing radiation therapy, though fatigue may take longer to resolve. Follow-up appointments will monitor your recovery and check for any recurrence. Skin in the treated area may remain sensitive to sun exposure permanently.

Completing radiation therapy is an important milestone, but recovery is a gradual process. Understanding what to expect during the weeks and months after treatment can help you navigate this transition successfully.

Immediate Post-Treatment Period

In the first few weeks after finishing radiation, you may notice that some side effects temporarily worsen before they improve. This is normal - radiation continues to damage cells for a short time after the last treatment, and the body needs time to begin healing. Skin reactions, for example, often peak about one to two weeks after completing treatment.

Continue following the skin care and other supportive measures recommended by your care team during this period. Fatigue may persist for several weeks or even months, so be patient with yourself and gradually increase activities as your energy returns. Most patients feel significantly better within two to three months after finishing treatment.

Follow-Up Care

You will have regular follow-up appointments with your radiation oncologist and other members of your cancer care team. These visits typically occur every few months initially and become less frequent over time. The purpose of follow-up is to monitor your recovery, manage any ongoing side effects, and check for signs of cancer recurrence.

Follow-up visits may include physical examinations, blood tests, and periodic imaging scans depending on your cancer type and treatment. Be sure to report any new symptoms or concerns at these appointments. Keep track of any side effects you experience so you can discuss them with your doctor.

Long-Term Considerations

Some effects of radiation therapy require ongoing attention:

• Sun protection: Treated skin may be permanently more sensitive to sunlight. Use sunscreen and protective clothing on the treated area whenever exposed to the sun.
• Dental care: If you had head and neck radiation, continue excellent oral hygiene and regular dental visits to prevent complications from dry mouth.
• Exercise and nutrition: Physical activity and healthy eating support recovery and overall health after cancer treatment.
• Emotional health: Cancer treatment can be emotionally challenging. Seek support from family, friends, support groups, or mental health professionals if needed.

Survivorship Care

As you move further from treatment, your care transitions to survivorship mode. This focuses on maintaining health, monitoring for late effects, and screening for recurrence. Ask your care team about a survivorship care plan, which summarizes your treatment history and outlines recommended follow-up care.

Many cancer centers offer survivorship programs that provide resources for nutrition, exercise, stress management, and managing long-term effects of treatment. Taking an active role in your ongoing health can help you feel more in control and improve your quality of life after treatment.

Are There Special Considerations for Children and Fertility?

Children may experience unique long-term effects from radiation including impacts on growth and development. Fertility can be affected when radiation is given near reproductive organs, but fertility preservation options exist. Radiation therapy should be postponed during pregnancy whenever possible.

Certain patient populations require special consideration when planning radiation therapy. Understanding these factors can help patients and families make informed decisions and prepare for potential long-term effects.

Radiation Therapy in Children

While radiation therapy can be highly effective for pediatric cancers, children's developing bodies are more susceptible to long-term effects. The radiation team carefully considers the potential impact on growth, organ development, and future cancer risk when treating young patients.

Potential late effects in children may include:

• Effects on growth in bones and soft tissues within the treatment field
• Hormonal changes if the pituitary gland or thyroid is affected
• Cognitive effects from brain radiation
• Impacts on fertility when reproductive organs are treated
• Small increased risk of secondary cancers later in life

Pediatric radiation oncologists use techniques specifically designed to minimize these risks, including lower doses when appropriate and advanced targeting technologies like proton therapy. Long-term follow-up continues into adulthood to monitor for and address any late effects.

Fertility Considerations

Radiation therapy to the pelvic area or abdomen can affect fertility in both men and women. The impact depends on the radiation dose, the treatment area, and the patient's age. Before beginning treatment, discuss fertility concerns with your oncologist - there may be options for preserving fertility.

For women, options may include moving the ovaries out of the radiation field (oophoropexy) or freezing eggs or embryos before treatment. For men, sperm banking before radiation begins can preserve the option for biological children later. Even for children and adolescents, fertility preservation should be discussed before treatment when radiation may affect reproductive organs.

Pregnancy and Radiation

Radiation therapy during pregnancy poses risks to the developing fetus and is generally avoided whenever possible. If you are or might be pregnant, inform your medical team immediately before starting treatment. In most cases, treatment can be delayed until after delivery or modified to protect the fetus.

In rare situations where cancer must be treated urgently during pregnancy, careful shielding and modified treatment techniques may allow radiation to be given while minimizing fetal exposure. These decisions are made on a case-by-case basis by a multidisciplinary team including maternal-fetal medicine specialists.

Breastfeeding Considerations

If you are breastfeeding and need radiation therapy, discuss this with your care team. External beam radiation therapy does not make breast milk radioactive. However, if you receive systemic radiation (radioactive drugs), you will need to stop breastfeeding temporarily or permanently depending on the specific treatment. Your oncologist can provide guidance based on your specific situation.

Is Radiation Therapy Safe for People Around You?

External beam radiation therapy does not make you radioactive - you can safely be around family members, children, and pregnant women immediately after treatment. With brachytherapy or systemic radiation, temporary precautions may be needed while the radioactive material is active in your body.

One of the most common concerns patients have is whether their radiation treatment poses any risk to people around them. Understanding the facts can help alleviate unnecessary worry and ensure appropriate precautions are taken when needed.

External Beam Radiation Safety

With external beam radiation therapy, the radiation beams pass through your body during treatment but do not remain in your body afterward. As soon as the treatment machine is turned off, there is no residual radiation. You are not radioactive and cannot expose others to radiation through normal contact, sharing food, or any other activities.

You can safely hug your family members, play with children, and interact normally with pregnant women after external beam radiation treatments. There are no restrictions on who you can be around or activities you can do (other than any limitations related to your own side effects or energy level).

Internal Radiation and Systemic Radiation Safety

With brachytherapy or systemic radiation therapy (radioactive drugs), the situation is different because radioactive material is placed in or enters your body. Temporary safety precautions may be needed:

Permanent seed implants (like those used for prostate cancer) contain low-energy radiation that is mostly absorbed by surrounding tissue. While special precautions are not usually needed, some doctors recommend limiting close contact with pregnant women and small children for the first few months.

Temporary brachytherapy sources are removed after treatment, so once you leave the treatment facility, you are not radioactive.

Systemic radiation therapy (like radioactive iodine for thyroid cancer) may require isolation for several days and specific precautions for one to two weeks after treatment. Your medical team will provide detailed instructions about maintaining distance from others, using separate bathrooms if possible, and other safety measures.

Always follow the specific guidance provided by your radiation oncology team, as recommendations vary based on the type and amount of radiation used in your treatment.

Editorial Team

This article was created by the iMedic Medical Editorial Team, a group of licensed healthcare professionals with expertise in oncology and radiation medicine.

All content follows international guidelines from ASTRO, ESMO, and WHO. For questions about this article, please visit our contact page.