Radiation Therapy: A Complete Treatment Guide

How Radiation Therapy Works

Radiation therapy (also called radiotherapy) uses high-energy particles or waves, such as X-rays, gamma rays, electron beams, or protons, to destroy cancer cells. The radiation damages the DNA inside cancer cells so severely that the cells can no longer repair themselves and eventually die. While radiation also affects nearby healthy cells, normal cells are generally better at repairing DNA damage than cancer cells, which is why treatment is given in multiple small doses over several weeks.

A radiation oncologist is the specialist who designs your treatment plan, determines the appropriate dose, and oversees your care throughout treatment. They work alongside medical physicists and dosimetrists who calculate precise radiation doses and radiation therapists who operate the equipment and position you for each session.

Types of Radiation Therapy

External Beam Radiation Therapy (EBRT)

External beam radiation is the most common form of radiation therapy. A machine called a linear accelerator (linac) directs high-energy beams at the tumor from outside the body. You do not become radioactive during or after treatment. Several advanced techniques fall under external beam radiation:

Three-Dimensional Conformal Radiation Therapy (3D-CRT)

Uses CT scans to create a three-dimensional model of the tumor and surrounding structures. Multiple radiation beams are then shaped to match the tumor's contour, reducing exposure to nearby healthy tissue compared to older techniques.

Intensity-Modulated Radiation Therapy (IMRT)

An advanced form of 3D-CRT that modulates (adjusts) the intensity of each radiation beam. This allows the radiation oncologist to deliver different doses to different areas within the treatment field, concentrating higher doses on the tumor while keeping doses to critical organs low. IMRT is widely used for prostate cancer, head and neck cancers, and brain tumors.

Stereotactic Body Radiation Therapy (SBRT)

Delivers very high doses of precisely focused radiation in a small number of sessions (typically one to five treatments). SBRT is used for small, well-defined tumors in the lung, liver, spine, and other locations. The extreme precision allows ablative doses that destroy the tumor while sparing surrounding tissue. For brain tumors, this technique is called stereotactic radiosurgery (SRS).

Proton Therapy

Uses protons instead of X-rays. The key advantage of proton therapy is the Bragg peak, a physical property that causes protons to deposit most of their energy at a precise depth, with very little radiation passing beyond the tumor. This makes proton therapy especially valuable for pediatric cancers and tumors near critical structures like the brain, spinal cord, and eyes. Proton therapy centers are less common and typically more expensive than conventional radiation facilities.

Brachytherapy (Internal Radiation)

Brachytherapy involves placing a radioactive source directly inside or next to the tumor. This delivers a very high dose of radiation to a small area while limiting exposure to surrounding tissues. There are two main types:

• High-dose-rate (HDR) brachytherapy: A radioactive source is temporarily placed into the body through catheters or applicators for a few minutes at a time. Multiple sessions may be needed. Common for cervical cancer and some breast cancers.
• Low-dose-rate (LDR) brachytherapy: Radioactive seeds or pellets are permanently implanted into the tumor, where they slowly release radiation over weeks or months. Frequently used for early-stage prostate cancer.

When Radiation Therapy Is Used

Curative Radiation

Radiation may be the primary treatment for certain cancers, particularly when surgery is not feasible or when the tumor responds well to radiation. It is also commonly used after surgery (adjuvant radiation) to eliminate microscopic cancer cells that may remain, reducing the risk of recurrence. In some cases, radiation is given before surgery (neoadjuvant radiation) to shrink a tumor and make it easier to remove.

Concurrent Chemoradiation

Radiation is frequently combined with chemotherapy because certain chemo drugs make cancer cells more sensitive to radiation. This combination is standard treatment for many cancers of the head, neck, lung, cervix, and rectum.

Palliative Radiation

When a cure is not possible, radiation can provide significant symptom relief. Palliative radiation can shrink tumors that are causing pain, bleeding, difficulty swallowing, or airway obstruction. Bone metastases frequently respond well to palliative radiation, with many patients experiencing meaningful pain relief within one to two weeks.

Treatment Planning and Simulation

Before your first radiation treatment, you will undergo a planning session called a simulation. This session typically takes 30 to 60 minutes and involves the following steps:

1. Imaging: A CT scan (and sometimes MRI or PET scan) is performed in the exact position you will be in during treatment
2. Immobilization: Custom molds, masks, or cushions are created to help you hold the same position for each treatment session
3. Marking: Small tattoo dots or skin marks are placed to ensure precise alignment each day
4. Planning: Your radiation oncologist and physics team use the imaging data to design a treatment plan that maximizes the dose to the tumor while minimizing exposure to nearby organs

The planning process may take one to two weeks before treatment begins. This time is essential for creating a safe, effective treatment plan.

What Happens During a Treatment Session

A typical external beam radiation session lasts 15 to 30 minutes from arrival to departure, though the actual radiation delivery takes only one to five minutes. You will lie on a treatment table while the radiation therapist positions you using the alignment marks made during simulation. The linear accelerator may rotate around you to deliver radiation from multiple angles.

You will be alone in the treatment room during radiation delivery, but your treatment team monitors you through cameras and an intercom system. The machine does not touch you, and you will not feel anything during the radiation delivery. Some patients hear clicking or buzzing sounds from the machine.

Most patients receive treatment five days per week (Monday through Friday) for several weeks. Some newer protocols use fewer sessions with higher doses per session (hypofractionation).

Side Effects by Treatment Area

Radiation side effects are generally limited to the area being treated. They tend to develop gradually over the course of treatment and may continue for a few weeks after treatment ends before improving.

General Side Effects (Any Area)

• Skin changes: Redness, dryness, peeling, or darkening in the treated area, similar to a sunburn
• Fatigue: Usually builds gradually over the course of treatment

Head and Neck

• Mouth sores (mucositis) and difficulty swallowing
• Dry mouth (xerostomia) due to salivary gland damage
• Taste changes, dental problems
• Sore throat, hoarseness

Chest and Breast

• Difficulty swallowing (esophagitis) if the esophagus is in the treatment field
• Cough, shortness of breath (radiation pneumonitis, typically weeks after treatment)
• Breast swelling, skin irritation (for breast radiation)

Abdomen and Pelvis

• Nausea, diarrhea, cramping
• Bladder irritation (urinary frequency, urgency, burning)
• For pelvic radiation: sexual side effects, fertility concerns

Recovery After Radiation Therapy

Most acute side effects from radiation begin to improve within two to four weeks after treatment ends, though some effects, particularly fatigue, may persist for several months. Late side effects, which can develop months or years after treatment, are less common but may include tissue fibrosis (scarring), changes in skin texture, or, rarely, secondary cancers in the treated area.

During recovery, continue to protect your skin in the treated area from sun exposure. Follow up with your radiation oncologist as scheduled, typically at four to six weeks after completing treatment, then at regular intervals. Report any new or worsening symptoms, as some side effects can develop after a delay.

Last reviewed: March 2026. This information is for educational purposes only and is not a substitute for professional medical advice. Always consult your radiation oncologist about your specific treatment plan.