A cancer diagnosis floods you with new vocabulary overnight, and “radiation therapy” is almost always in the pile.
So here is the plain-English version: radiation therapy uses focused beams of high-energy particles or waves to damage the DNA inside cancer cells so they can no longer grow and divide, ideally while limiting the dose to the healthy tissue around them.
It has been a cornerstone of cancer care for decades, and it is not a single treatment but a whole family of them. Understanding how the types of radiation therapy differ can turn a nerve-racking appointment into a conversation you feel ready to have.
What Are the 3 Types of Radiation Therapy?
The three main types of radiation therapy are external beam radiation therapy, internal radiation therapy (brachytherapy), and systemic radiation therapy. The simplest way to tell them apart is to ask one question: where does the radiation start?
External beam radiation therapy delivers radiation from a machine outside the body, aiming high-energy beams through the skin to the tumor. It is the most common type, and it treats one targeted area at a time.
Brachytherapy, also called internal radiation therapy, places a small solid radioactive source, such as a seed, pellet, or wire, directly inside or beside the tumor, so the dose stays concentrated right where it is needed.
Systemic radiation therapy uses a liquid radioactive drug that you swallow or receive through an IV, allowing it to travel through the bloodstream and reach cancer cells throughout the body.
From there, your radiation oncologist chooses the approach, or the combination, that best fits each patient’s situation.
External Beam Radiation Therapy
To get into a bit more detail, external beam radiation therapy is the workhorse most people picture: a machine moves around your body and directs high-energy beams at the tumor without ever touching your skin.
Most treatment relies on photons, better known as X-rays, though the category now includes more precise tools such as intensity-modulated radiation therapy (IMRT), stereotactic radiosurgery (SRS), and proton therapy.
Proton therapy changes the underlying physics. Instead of X-rays, it uses protons, heavier particles that release most of their energy right at the tumor and then stop, rather than passing through the rest of the body.
Picture traditional radiation as a bullet that keeps traveling after it hits its target, while proton therapy is more like an arrow that stops exactly where it lands. Because of that, proton therapy may help reduce the radiation that reaches nearby healthy tissue, which can matter most for tumors near the brain, spine, or eyes, and for children whose bodies are still growing.
Internal Radiation Therapy (Brachytherapy)
Brachytherapy works from the inside out. A doctor places a tiny sealed source, such as a seed, pellet, or wire, directly into or beside the tumor, so the dose stays concentrated in one small area and may help limit the radiation reaching nearby tissue.
It is a common choice for prostate, cervical, and certain breast and head and neck cancers, and the source may stay in place permanently or come out after a set time, depending on the treatment plan.
Systemic Radiation Therapy
Systemic radiation therapy takes a whole-body approach. You either swallow a radioactive drug or receive it through an IV, then it travels through the bloodstream and seeks out cancer cells on its own.
Radioactive iodine for certain thyroid cancers is the classic example, and a new wave of targeted radioactive drugs keeps widening what this treatment can reach.
How Does Radiation Therapy Work?
Every type of radiation therapy shares the same goal: damaging the DNA inside cancer cells until they can no longer repair themselves and divide. Healthy cells get caught in the crossfire too, but they are generally better at fixing that damage and bouncing back, which is the whole reason treatment is usually split into small daily doses over several days or weeks.
Those breaks give your healthy tissue time to recover between sessions while the tumor keeps absorbing hits it cannot come back from. It also explains something that surprises a lot of patients: the work is not finished when you walk out the door. Cancer cells often keep dying for weeks after your final session, so tumors can continue to shrink well after treatment ends.
Take the Next Step With Emory Proton Therapy Center
If you are wondering whether proton therapy is right for you, that is exactly the conversation the team at Emory Proton Therapy Center is here to have.
As part of Emory Healthcare, our radiation oncologists will review your case, explain your options in clear terms, and help you understand whether proton therapy may be appropriate, so you never have to navigate this alone. Schedule your consultation today and take a confident first step toward advanced, personalized cancer care.