Radiation Therapy for Cancer

Introduction

If you or someone you care for has been told that radiation therapy is part of the cancer treatment plan, you are likely trying to understand what the weeks ahead will look like. Radiation therapy is one of the three main pillars of cancer treatment, alongside surgery and drug therapy (chemotherapy, immunotherapy, hormone therapy, and targeted treatments). About half of all people with cancer receive radiation therapy at some point in their treatment journey.

This article explains what radiation therapy is, how it works, the different techniques used today, what to expect during a course of treatment, the side effects that may appear and how they are managed, and how radiation fits with other cancer treatments. It is written for patients and families who already have a diagnosis and are preparing for, currently receiving, or recovering from radiation treatment.

Radiation therapy has changed substantially over the past two decades. Modern techniques allow radiation oncologists to shape the dose tightly around a tumour while sparing healthy tissue, which has reduced side effects and improved outcomes for many cancer types. The plan that has been built for you is highly individual — it depends on the cancer type, its location and stage, the goal of treatment, and your overall health.

What Is Radiation Therapy?

Radiation therapy, sometimes called radiotherapy, is the use of high-energy radiation to kill cancer cells or stop them from growing. The most common form uses high-energy X-ray beams produced by a machine called a linear accelerator (often shortened to “linac”). Other forms use protons, gamma rays, electrons, or radioactive sources placed inside or near the tumour.

Radiation works by damaging the DNA inside cancer cells. Once the DNA is damaged beyond repair, the cell can no longer divide and eventually dies. Healthy cells in the radiation field also receive some dose, but they are generally better at repairing DNA damage than cancer cells. By spreading the total dose over many small daily treatments — called fractions — the radiation team gives healthy tissue time to repair between sessions while cancer cells gradually accumulate enough damage to die. This is one of the core principles behind a typical course of radiation therapy.

Radiation therapy can be given with several different intents:

• Curative (radical) intent: to eliminate the cancer entirely, either alone or combined with other treatments. Examples include radiation for early-stage prostate cancer, certain head and neck cancers, cervical cancer, and some lung and skin cancers.
• Adjuvant intent: given after surgery to reduce the chance of the cancer coming back. Common after breast-conserving surgery for breast cancer and after surgery for some brain tumours, for example.
• Neoadjuvant intent: given before surgery to shrink the tumour and make removal easier or safer. Used in rectal cancer, some sarcomas, and certain oesophageal cancers.
• Palliative intent: given to relieve symptoms caused by cancer, such as pain from bone metastases, bleeding, or pressure on nearby structures. Palliative courses are usually shorter than curative ones.

Knowing the intent of your radiation course helps you understand the schedule, the dose, and the likely side effects. Curative treatments typically use higher total doses spread over more weeks, while palliative treatments often use fewer, larger doses focused on quick symptom relief.

How Radiation Therapy Works

Cancer cells, like all cells, contain DNA — the instructions a cell uses to grow and divide. When a beam of radiation passes through tissue, it knocks electrons off atoms in the cells, creating reactive particles that damage the DNA strands. Some of this damage can be repaired; some cannot. Cancer cells, because they divide rapidly and often carry faulty repair machinery, are generally more vulnerable to this damage than the surrounding normal cells.

• Targeting: deliver enough dose to the tumour to kill it.
• Sparing: keep the dose to nearby healthy organs (called “organs at risk”) as low as possible.
• Fractionation: divide the total dose into smaller daily treatments to give normal tissue time to recover.

Modern imaging and computer planning have made these three principles work together far more precisely than was possible in earlier decades. Three-dimensional scans of your body are used to build a custom plan, and the radiation beams are shaped to match the tumour from multiple angles. Daily imaging on the treatment machine confirms your position before each session.

Who Receives Radiation Therapy?

Radiation therapy is used across most cancer types. Whether it is offered to you depends on the cancer’s type, location, stage, and your overall health. Some of the more common situations include:

• Breast cancer: radiation to the breast after lumpectomy (breast-conserving surgery) is standard practice. It may also be given after mastectomy in some situations, and to lymph node areas when needed.
• Prostate cancer: radiation is one of the main curative options for localised prostate cancer, either as external beam radiation or brachytherapy.
• Lung cancer: radiation may be given alone for early-stage tumours in people who cannot have surgery (often as stereotactic body radiation therapy), combined with chemotherapy for locally advanced disease, or used to treat symptoms in advanced disease.
• Head and neck cancers: radiation, often combined with chemotherapy, is a major treatment for cancers of the throat, voice box, mouth, and salivary glands.
• Cervical and other gynaecological cancers: radiation, usually combining external beam treatment with brachytherapy, is central to the treatment of locally advanced cervical cancer.
• Rectal cancer: radiation combined with chemotherapy is often given before surgery to shrink the tumour.
• Brain tumours: radiation is used after surgery for many primary brain tumours and for some brain metastases.
• Lymphomas: radiation plays a role in certain Hodgkin and non-Hodgkin lymphomas, often combined with chemotherapy.
• Skin cancers: radiation is one option for certain non-melanoma skin cancers when surgery is not preferred.
• Bone metastases and other palliative settings: short courses of radiation can relieve pain, control bleeding, or reduce pressure on the spinal cord.

Several different techniques fall under the broad heading of radiation therapy. The radiation oncologist chooses the technique based on the tumour’s location, size, shape, and proximity to sensitive organs, and on the overall treatment goal.

External Beam Radiation Therapy (EBRT)

Within EBRT, several modern techniques exist:

• Three-dimensional conformal radiation therapy (3D-CRT): uses CT-based planning to shape beams to the tumour. It was the standard approach before more advanced techniques became widely available and is still used for some indications.
• Intensity-modulated radiation therapy (IMRT): uses many small beam segments of varying intensity to sculpt the dose tightly around irregularly shaped tumours. Particularly useful for head and neck, prostate, and gynaecological cancers where critical structures sit very close to the tumour.
• Volumetric modulated arc therapy (VMAT): a refinement of IMRT in which the treatment machine rotates around you while delivering radiation continuously, often shortening each session.
• Image-guided radiation therapy (IGRT): uses imaging on the treatment machine — CT scans, X-rays, or other systems — immediately before or during each session to verify your position. IGRT is now standard with most modern EBRT plans.

Stereotactic Radiation Therapy: SRS and SBRT

Stereotactic techniques deliver very high doses of radiation in a small number of highly precise sessions.

• Stereotactic radiosurgery (SRS) treats small targets in the brain, usually in one session. Despite the name, no incision is involved — the “surgery” refers to the precision. SRS is used for brain metastases, some benign brain tumours, and certain functional disorders.
• Stereotactic body radiation therapy (SBRT), sometimes called SABR (stereotactic ablative radiotherapy), treats small targets elsewhere in the body — lung, liver, spine, prostate, adrenal — usually in three to five sessions.

These techniques require sophisticated immobilisation, imaging, and motion management, especially for tumours that move with breathing.

Brachytherapy

Brachytherapy (from the Greek brachys, meaning short) places radioactive sources directly inside or next to the tumour. Because the radiation acts over very short distances, healthy tissues a few centimetres away receive a much lower dose than with external beam.

Brachytherapy is used most commonly for:

• Cervical and uterine cancers (intracavitary brachytherapy)
• Prostate cancer (permanent seed implants or temporary high-dose-rate brachytherapy)
• Selected breast cancers (as part of partial breast irradiation in some patients)
• Skin cancers and certain head and neck cancers

Brachytherapy can be high-dose-rate (HDR), delivered over minutes through temporarily inserted applicators, or low-dose-rate (LDR), delivered over hours or days, sometimes using permanent implants such as prostate seeds.

Proton Therapy

Proton therapy uses charged particles (protons) rather than X-rays. Protons deposit most of their energy at a specific depth inside the body (the “Bragg peak”) and then stop, so they deliver less dose to tissues beyond the tumour. This makes proton therapy particularly useful for tumours near critical structures and for children, in whom limiting dose to growing tissues matters more. Proton therapy is available at a limited number of centres worldwide and is selected for specific clinical situations rather than offered as a general alternative to X-ray radiation.

Internal Radiation with Radioactive Drugs (Systemic Radioisotope Therapy)

In some cancers, a radioactive substance is given as an injection, capsule, or infusion and travels through the body to reach cancer cells. Examples include radioactive iodine for thyroid cancer, radium-223 for prostate cancer with bone metastases, and lutetium-based therapies for certain neuroendocrine and prostate cancers. These treatments are sometimes grouped under the term “radioligand therapy” or “radionuclide therapy.”

Intraoperative Radiation Therapy (IORT)

IORT delivers radiation directly to the tumour bed during surgery, after the tumour has been removed and before the wound is closed. It is used selectively in some breast cancers, sarcomas, and abdominal cancers.

The Treatment Plan and What to Expect

Once the decision to give radiation has been made, you will go through several preparation steps before treatment begins.

Consultation and Planning

You will first meet the radiation oncologist, who will review your imaging, pathology, and overall health, and explain the proposed plan: the technique, the total dose, the number of fractions, the schedule, the goal of treatment, and the expected side effects. This is an important conversation; bringing a family member and a written list of questions is helpful.

Simulation

Before treatment starts, you will undergo a planning session called “simulation.” A CT scan, and sometimes an MRI or PET scan, is taken in the exact position you will be in for treatment. Custom devices — a mesh mask for head and neck treatment, a body cradle, breath-hold instructions for breast or lung treatment — may be made to keep you still and reproducible. Small permanent skin marks (tiny tattoos) or temporary marks may be placed to help the team align you the same way every day.

Plan Design

The radiation oncologist, working with medical physicists and dosimetrists, designs the radiation plan on a computer. They define the tumour (called the target volume), the surrounding organs to protect (organs at risk), and choose beam angles, shapes, and intensities to deliver the prescribed dose to the tumour while keeping healthy tissue below safe limits. Quality checks are performed on the plan before any treatment is given. This planning step usually takes one to two weeks.

Daily Treatment

Most external beam courses involve treatment Monday through Friday, with weekends off, for a number of weeks that depends on the cancer type and intent. Each session typically takes 15 to 30 minutes, of which only a few minutes is the actual radiation. You lie still on the couch, the team positions you precisely, imaging confirms your alignment, and the machine then delivers the beams from several angles. You will not feel the radiation as it is given. The room is empty during treatment, but the team watches and listens to you on video and can pause the treatment if needed.

On-Treatment Reviews

While you are receiving radiation, you will have regular check-ins with the radiation oncologist or radiation nurse — commonly weekly — to review how you are tolerating treatment, manage side effects, and adjust supportive care.

Length of Treatment

Course length varies widely:

• A single fraction for a painful bone metastasis
• Three to five fractions for stereotactic body radiation
• One to three weeks for some shorter (hypofractionated) breast and prostate schedules
• Five to seven weeks for many head and neck, cervical, and prostate curative courses
• Several days of brachytherapy for cervical cancer, in addition to external beam radiation

Side Effects and How They Are Managed

Side effects from radiation therapy fall into two broad groups: acute (during or shortly after treatment) and late (months to years afterwards). The specific side effects depend almost entirely on which part of the body is being treated, because radiation affects mainly the tissues in or close to the radiation field. Side effects from radiation to the prostate are very different from side effects from radiation to the head and neck.

Acute Side Effects

Most acute side effects begin a week or two into treatment, peak near the end or shortly after, and resolve over several weeks. Common acute effects include:

• Fatigue: very common across most radiation sites. It builds gradually through the course and usually improves over weeks after treatment ends.
• Skin reactions: redness, dryness, itching, and sometimes peeling or moist breakdown in the treated area. Gentle skincare advised by your team helps.
• Hair loss in the treated area only: radiation does not cause hair loss elsewhere in the body (unlike chemotherapy). Hair regrowth may or may not occur, depending on dose.

Site-specific acute effects include:

• Head and neck radiation: sore mouth and throat, taste changes, dry mouth, thick saliva, difficulty swallowing, voice changes. Nutritional support, mouth care, and sometimes a temporary feeding tube may be needed.
• Chest radiation: oesophagitis (sore swallowing), cough, and shortness of breath.
• Abdominal or pelvic radiation: nausea, diarrhoea, urinary frequency or burning, and sometimes rectal irritation.
• Breast radiation: skin redness, breast swelling and tenderness.
• Brain radiation: fatigue, hair loss in the treated area, mild headache, and sometimes nausea.

The radiation team has many tools to manage acute side effects: skincare products, anti-nausea medications, mouthwashes, pain relief, dietary advice, and adjustment of the treatment plan if needed. Telling the team early about any new symptom helps keep treatment on track without unplanned breaks.

Late Side Effects

Late effects appear months or years after treatment. They are less common with modern, precisely targeted radiation than they were with older techniques, but they can be more persistent. Possible late effects depend on the site treated and may include:

• After head and neck radiation: long-term dry mouth, dental problems, jaw stiffness, changes in swallowing, and rarely hypothyroidism if the thyroid gland was in the field.
• After chest radiation: lung scarring (pneumonitis or fibrosis), and small long-term effects on the heart in some breast cancer patients (much reduced with modern techniques and breath-hold methods).
• After pelvic radiation: long-term bowel changes, urinary changes, sexual changes, and infertility. Fertility-preserving discussions before treatment are important for younger patients.
• After brain radiation: memory and concentration changes, particularly with whole-brain radiation; these are much less prominent with focused stereotactic treatment.
• Lymphoedema: swelling of an arm or leg after radiation to nearby lymph nodes (most often after breast or pelvic radiation combined with lymph node surgery).
• Second cancers: a small long-term risk of a new cancer developing in or near the radiation field, generally many years later. This risk is weighed against the benefit of treating the original cancer.

Your follow-up plan after radiation includes monitoring for late effects relevant to your treated area.

Response and Monitoring

Radiation continues to work after the last treatment session. Cancer cells whose DNA has been damaged beyond repair die over the following weeks and months. For some cancers, tumour shrinkage on scans is visible within a few weeks; for others, it takes several months for the full response to become clear. This is why scans are usually not repeated immediately after radiation ends.

Follow-up after a curative course typically involves:

• Clinical reviews at scheduled intervals, more frequent in the first one to two years
• Imaging (CT, MRI, PET, or ultrasound) on a schedule that depends on the cancer type
• Blood tests, including tumour markers where relevant (for example, PSA for prostate cancer)
• Endoscopic or visual examination of the treated site for head and neck, cervical, and some other cancers
• Late-effects monitoring relevant to the site treated

Different cancer types have different patterns of recurrence risk, and the follow-up schedule is built around those patterns. The doctors will explain what specific symptoms to report between visits.

Combining Radiation with Other Treatments

Radiation is often used together with other cancer treatments. The combination is chosen based on the cancer type and how the treatments interact.

Radiation and Surgery

Radiation may be given before surgery to shrink a tumour and make removal more feasible, or after surgery to reduce the risk of the cancer returning. Examples include preoperative radiation for rectal cancer and postoperative radiation after breast-conserving surgery.

Radiation and Chemotherapy

When chemotherapy is given at the same time as radiation, it is called concurrent chemoradiation. Certain chemotherapy drugs make cancer cells more sensitive to radiation. Concurrent chemoradiation is standard for many locally advanced cancers, including head and neck, cervical, anal, oesophageal, and some lung cancers. Side effects can be greater than with either treatment alone, so the team monitors closely.

Radiation and Targeted or Immunotherapy

Newer combinations are being studied actively. In some cancers, radiation is combined with targeted drugs (for example, cetuximab in some head and neck cancers) or with immunotherapy (for example, durvalumab after chemoradiation in certain lung cancers). The evidence base in this area is evolving, and your team will explain whether a combination is part of your plan.

Radiation and Hormone Therapy

For prostate cancer, hormone therapy is commonly combined with radiation in intermediate- and high-risk disease. For some breast cancers, hormone therapy follows radiation as part of the overall plan.

Living During and After Treatment

Going through a course of radiation is a daily commitment that can be tiring even when the immediate side effects are mild. Some practical things that may help:

• Plan for fatigue. Reduce non-essential commitments during treatment. Short walks and light activity have been shown to help energy levels rather than hurt them, but rest when you need to.
• Eat well. Nutritional support is part of cancer care, and many radiation centres have a dietitian. This is particularly important for head and neck, oesophageal, and abdominal radiation, where swallowing and digestion may be affected.
• Care for the treated skin. Use the products your team recommends. Avoid hot water, harsh soaps, and direct sun on the treated area during and for some time after treatment. Sun protection for treated skin remains important long-term.
• Stop smoking if you smoke. Smoking during radiation reduces its effectiveness in several cancer types and increases side effects. Support to stop is available and worth using.
• Watch for and report symptoms. Tell the team about pain, swallowing difficulty, skin breakdown, urinary or bowel symptoms, or anything new. Early management keeps small problems from becoming big ones.
• Look after your emotional health. Cancer treatment is demanding. Counselling, support groups, and conversations with your family doctor or oncology team are all reasonable. Anxiety and low mood during treatment are common and treatable.

After treatment ends, recovery is gradual. Fatigue may take weeks to months to lift fully. Skin reactions usually settle over several weeks. Late effects, when they occur, develop slowly, and follow-up is designed to catch them early.

Many people return to work, family life, and most activities once acute side effects have resolved. Survivorship care — the long-term phase that begins after treatment ends — addresses physical recovery, late effects, surveillance for recurrence, screening for new cancers, and emotional wellbeing. Major cancer societies, including ASCO and ESMO, emphasise structured survivorship planning as part of high-quality cancer care.

Radiation Therapy in Children

Children with cancer sometimes receive radiation as part of their treatment, but paediatric radiation is approached differently from adult radiation because children’s tissues are still growing and are more sensitive to radiation’s long-term effects.

Some specific considerations for paediatric radiation:

• Avoiding or minimising radiation where possible. Modern paediatric oncology protocols try to reduce or omit radiation when other treatments are equally effective, particularly for young children.
• Proton therapy. Where available, proton therapy is often preferred for children because it reduces the dose to surrounding growing tissues. Major paediatric oncology groups support its use for selected paediatric tumours.
• Anaesthesia for young children. Lying perfectly still for treatment can be difficult for young children. Brief general anaesthesia for each session may be needed and is given by a paediatric anaesthesia team.
• Long-term follow-up. Children who receive radiation are followed for many years afterwards. Possible late effects include impact on growth, hormone production, cognition (with brain radiation), fertility, heart and lung function (depending on the site), and a small increased risk of second cancers later in life. Structured survivorship clinics for childhood cancer survivors monitor for these effects.

Decisions about paediatric radiation are made by multidisciplinary teams that include paediatric oncologists, radiation oncologists with paediatric experience, paediatric anaesthetists, and child life specialists. Parents are part of every step.

Frequently Asked Questions

Will I be radioactive during or after treatment?

For external beam radiation, no. You are not radioactive at any point and it is safe to be around your family, including children and pregnant women. For brachytherapy with permanent implants (such as some prostate seed implants), there are simple safety instructions for the first few weeks, which your team will explain. For systemic radioactive treatments (such as radioactive iodine), short-term precautions about contact with others are needed for a few days; the team will give specific instructions.

Does radiation therapy hurt?

The treatment itself is painless. You do not feel the radiation as it is given. Some side effects, such as sore mouth or skin reactions, can be uncomfortable and are managed with medications and supportive care.

Will I lose my hair?

Radiation causes hair loss only in the treated area. If your scalp is not in the radiation field, your scalp hair will not fall out. Brain radiation does cause scalp hair loss; whether it regrows depends on the dose.

Can I work during radiation therapy?

Many people continue working, particularly if their job is not physically demanding and they can attend daily appointments. Fatigue may build over the course of treatment, and roles vary in how taxing they are. Your radiation oncologist or nurse can help you think through what is realistic for your situation.

Can I drive myself to treatment?

Most people can drive themselves to external beam radiation sessions, especially early in the course. Towards the end of a long course, fatigue may make a companion driver helpful. For brachytherapy procedures involving sedation or anaesthesia, you will need a driver afterwards.

What if I miss a treatment?

Missing the occasional session because of illness or unavoidable circumstances is usually manageable; the team will add a session at the end. Multiple missed sessions can affect the effectiveness of the course, particularly for fast-growing cancers, so let the team know as soon as possible if you cannot attend.

Can radiation therapy be repeated to the same area?

In some situations, re-irradiation of a previously treated area is possible, particularly with modern stereotactic techniques. The previous dose, the time gap, the tolerance of surrounding tissues, and the goal of treatment all factor into the decision. Re-irradiation is a specialised situation and is considered carefully.

Will radiation cause another cancer?

There is a small long-term risk that radiation can contribute to a new cancer developing many years later in or near the treated area. The risk is small compared with the benefit of treating the cancer that is being addressed now, and modern techniques that limit dose to healthy tissue have reduced this risk further. Follow-up after treatment includes attention to this possibility.

Does radiation affect fertility?

Radiation to the pelvis or to the brain (which can affect hormone control) can reduce fertility, sometimes permanently. If fertility matters to you, ask about preservation options — such as sperm banking, egg or embryo freezing, or ovarian tissue preservation — before treatment starts. Time is often a factor, so raise the question early.

Can I take vitamins, herbal supplements, or antioxidants during treatment?

This is worth discussing with your radiation oncologist. Some supplements, particularly high-dose antioxidants, may interfere with how radiation works. Routine multivitamins at standard doses are usually fine, but check with the team about anything specific.

How will the team know whether radiation has worked?

Response is assessed with a combination of clinical examination, imaging, blood tests, and sometimes biopsy or endoscopy, on a schedule built around the cancer type. Because cancer cells continue to die over weeks to months after radiation ends, the first response assessment is usually not immediate.

Conclusion

Radiation therapy is a powerful and precise cancer treatment that has changed substantially over the past two decades. It is used to cure some cancers, to lower the risk of recurrence after surgery, to make surgery feasible or safer, and to relieve symptoms when cancer is advanced. The technique, dose, schedule, and combinations with other treatments are tailored to each person’s cancer and overall situation.

Understanding the goal of your radiation, the technique being used, the schedule ahead of you, and the side effects to expect makes the weeks of treatment more manageable. Your radiation oncology team — radiation oncologist, radiation therapists, medical physicists, nurses, dietitians, and others — is there to guide you through every step, manage side effects, and follow you afterwards. The questions that come up along the way, whether about the daily routine, side effects, work, family, or what happens after treatment ends, are all worth asking.