“We will start with simulation, plan your fractions, and use IMRT with a boost.”
If that sounds like a foreign language, you are not alone. Many people hear these terms for the first time when they learn they need radiotherapy, often when it is hardest to take everything in.
Quick answer
Radiation oncology uses high-energy radiation primarily to treat cancer. Common terms include external beam radiation therapy (radiation from a machine outside the body), brachytherapy (radiation placed inside the body), IMRT and SBRT (different radiation delivery techniques), and fractions (individual treatment doses). This glossary explains them in simple language.
Why Do Radiotherapy Terms Feel So Confusing?
Radiotherapy has its own vocabulary, and nobody is born knowing it. This guide explains the terms you are most likely to hear, roughly in the order you may encounter them.
Not every term will apply to your treatment. Keep this guide handy, and ask your doctor to explain anything relevant to your care.
What Is Radiation Oncology? The Basics
Radiation oncology: The branch of medicine that uses high-energy radiation to treat cancer and, occasionally, selected non-cancerous conditions. Radiation damages cellular DNA, affecting cells’ ability to grow and divide. Cancer cells are often less able to repair this damage than healthy cells.
Role of Oncology Pharma Companies in Cancer Treatment
- Radiation oncology:
- The branch of medicine that uses high-energy radiation to treat cancer and, occasionally, selected non-cancerous conditions. Radiation damages cellular DNA, affecting cells' ability to grow and divide. Cancer cells are often less able to repair this damage than healthy cells.
- Radiation oncologist:
- A doctor who specialises in planning and overseeing radiation treatment, working with medical physicists, radiation therapists (technologists), nurses and other specialists.
- Radiotherapy / radiation therapy:
- Two names for the same treatment approach, using radiation primarily to treat cancer. The terms are interchangeable.
- Medical physicist and dosimetrist:
- Specialists who help calculate, plan and verify radiation doses and support accurate, safe treatment delivery.
How Is Radiation Therapy Given?
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External beam radiation therapy (EBRT):
The most common type. A machine outside the body directs radiation towards the treatment area. You cannot feel the radiation beam, and its delivery is usually painless.
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Linear accelerator (LINAC):
A machine commonly used for external beam radiotherapy. A movable part can rotate around you to deliver radiation from different planned angles.
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Brachytherapy:
A radiation source is placed inside the body, in or near the area being treated. It aims to deliver radiation to the target while limiting exposure to surrounding tissues.
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Systemic radiation therapy:
Radioactive medicines given by mouth or injection that travel through the body. They are used for specific cancers.
What Are the Different Radiotherapy Techniques?
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3D-CRT(three-dimensional conformal radiotherapy):
Uses imaging scans to create a 3D picture of the treatment area so radiation beams can be shaped to match it.
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IMRT(intensity-modulated radiotherapy):
Varies the radiation beam's intensity to shape the dose around the target while limiting exposure to nearby healthy tissues.
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VMAT(volumetric modulated arc therapy):
A type of IMRT that delivers radiation while part of the machine rotates around the patient. Treatment delivery may be faster than with some other techniques.
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IGRT(image-guided radiotherapy):
Uses imaging, such as X-rays or CT scans, before or during treatment to help verify patient positioning and guide radiation delivery.
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SBRT / SABR(stereotactic body radiotherapy / stereotactic ablative radiotherapy):
Delivers highly precise, relatively high radiation doses in a small number of sessions, usually for selected, well-defined targets outside the brain.
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SRS(stereotactic radiosurgery):
Despite its name, no cutting is involved. It delivers highly focused radiation, usually to targets in the brain or central nervous system, in one or a few sessions.
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Proton therapy:
Uses protons rather than conventional X-rays. Protons deposit much of their energy at a controlled depth, potentially reducing radiation exposure beyond the target. Its suitability and clinical benefit depend on the individual case; it is not necessary for every patient.
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Carbon ion therapy:
A form of particle therapy using heavier particles than protons. Available at limited specialised centres worldwide, it may be considered for selected clinical indications.
What Happens During Radiotherapy Planning? Key Terms
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Consultation:
Your first appointment, when the radiation oncologist reviews your medical history, reports and scans, and discusses whether radiotherapy is appropriate.
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Simulation (CT simulation):
A planning scan performed in the position intended for treatment. It helps the team map the treatment area and prepare your plan.
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Immobilisation device:
A mask, cushion or mould that helps you maintain a consistent position during treatment.
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Tattoo / skin marks:
Small reference marks that may be placed on the skin to assist accurate positioning. Not every patient needs permanent marks.
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Treatment plan:
A detailed, computer-generated plan showing how radiation will be delivered. Preparing and checking it may take several days.
Target volume (GTV, CTV, PTV):
Areas considered during radiation planning:
GTV (gross tumour volume): The tumour or visible disease identified through examination or imaging.
CTV (clinical target volume): The area requiring treatment because it contains known or potentially microscopic disease.
PTV (planning target volume): An additional planning margin that accounts for positioning differences and internal movement.
Organs at risk (OAR):
Healthy structures near the treatment area that the team aims to protect, such as the heart, lungs, spinal cord or bowel.
How Many Radiotherapy Sessions? Dose and Schedule Terms
Dose:
The amount of radiation prescribed for treatment.
Gray (Gy):
The unit used to measure absorbed radiation dose. One Gray equals one joule of energy absorbed per kilogram of tissue.
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Fraction:
One portion of the prescribed radiation dose, usually delivered during an individual treatment session. Dividing treatment into fractions can help healthy tissues recover between sessions.
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Fractionation:
The schedule used to divide radiation into treatment sessions. It may range from a single session to several weeks, depending on the treatment plan.
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Hypofractionation:
Uses fewer sessions with a higher dose per fraction than conventional schedules. It is suitable for selected clinical situations.
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Boost:
An additional radiation dose given to a selected area, either after the main treatment or during the same course.
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Course of treatment:
The complete set of radiation sessions planned for a patient.
Understanding Treatment Intent
Curative (radical) radiotherapy:
Treatment intended to eliminate cancer or achieve long-term disease control. A cure cannot be guaranteed.
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Adjuvant radiotherapy:
Radiation given after surgery to reduce the risk of cancer returning.
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Neoadjuvant radiotherapy:
Radiation given before surgery, sometimes to shrink a tumour.
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Concurrent chemoradiation:
Radiotherapy and chemotherapy given during the same treatment period.
Palliative radiotherapy:
Treatment primarily intended to relieve symptoms such as pain or bleeding and improve comfort, rather than cure the cancer.
What Are the Side Effects of Radiotherapy?
Acute side effects:
Effects developing during or shortly after treatment, such as fatigue or skin changes. Many improve over time, although some may last several weeks or longer.
Late side effects:
Effects that may appear months or years after treatment. Your doctor will explain the risks relevant to your treatment.
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Radiation dermatitis:
Skin changes in the treated area, ranging from mild redness or darkening to irritation and peeling.
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Mucositis:
Inflammation or soreness of the lining of the mouth or throat, which may occur when these areas receive radiation.
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Fatigue:
A common feeling of unusual tiredness during radiotherapy that may not improve with rest alone.
Response assessment / follow-up:
Check-ups, scans or tests used to assess treatment response, monitor recovery and identify possible side effects.
Side effects depend on the treatment area, dose, other treatments and individual health factors. Inform your care team about new or worsening symptoms rather than waiting for your next appointment.
Common Myths About Radiotherapy
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"Radiation therapy will make me radioactive."
External beam radiotherapy does not make you radioactive, and you are not a radiation risk to others after treatment. Some forms of internal radiation therapy may require specific precautions, which your team will explain.
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"Radiotherapy always causes severe side effects."
Not everyone experiences severe side effects. Their type and intensity vary, and modern techniques aim to limit unnecessary radiation exposure to healthy tissues.
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"The newest technology is always the best for me."
Not necessarily. The most suitable treatment depends on your cancer type, stage, location, overall health and treatment goals. Newer technology does not automatically mean better outcomes for every patient.
Five Questions to Ask Your Radiation Oncologist
Five Questions to Ask Your Radiation Oncologist
Frequently Asked Questions About Radiotherapy
What is the difference between radiotherapy and chemotherapy?
Radiotherapy usually directs radiation towards a specific treatment area, while chemotherapy uses medicines that generally travel throughout the body. Some patients receive both.
Is radiotherapy painful?
The radiation beam itself cannot usually be felt. However, positioning may cause discomfort, and side effects such as skin irritation or soreness can develop during or after treatment.
How long does radiotherapy take?
It varies from a single session to several weeks, depending on the cancer type, location and treatment goals. Your team will explain your schedule.
Will I be radioactive after radiotherapy?
Not after external beam radiotherapy. Certain internal radiation treatments may require temporary precautions, which your team will explain.
What is the difference between IMRT, IGRT and SBRT?
IMRT shapes the radiation dose, IGRT uses imaging to guide accurate delivery, and SBRT delivers precise, relatively high doses in a few sessions. These techniques may be used together when appropriate.
Key Takeaway
Radiotherapy has its own vocabulary, but understanding a few common terms can make treatment discussions easier.
Note down unfamiliar words during your appointments and ask your care team to explain them. Understanding your treatment and asking questions are important parts of your care.
References and Further Reading
- National Cancer Institute (NCI). Radiation Therapy to Treat Cancer.
https://www.cancer.gov/about-cancer/treatment/types/radiation-therapy - National Cancer Institute (NCI). External Beam Radiation Therapy for Cancer.
https://www.cancer.gov/about-cancer/treatment/types/radiation-therapy/external-beam - National Cancer Institute (NCI). Radiation Therapy Side Effects.
https://www.cancer.gov/about-cancer/treatment/types/radiation-therapy/side-effects - American Society for Radiation Oncology (ASTRO). RTAnswers: Glossary of Terms.
https://www.rtanswers.org/resources/glossary-of-terms
