radiotherapy
Meaning of radiotherapy: High-energy radiation aimed at a tumor to break its DNA, given in many small doses so healthy tissue can recover.
Definition of radiotherapy
Radiotherapy is the use of high-energy radiation to damage the DNA inside cancer cells so they can no longer divide. The radiation may be aimed from a machine outside the body, or a radioactive source may be placed inside, next to or within the tumor. Treatment is usually divided into many small doses spread over weeks.
How radiotherapy is built
- radi/o Combining form · Latin x-ray, radiation
- -therapy Suffix · Greek treatment
A medical term is read from its ending backwards: the suffix first, then the prefix, then the root. See all 223 word parts.
How does radiation kill a cancer cell?
Radiation strips electrons from the atoms it passes through. Most of the damage happens indirectly: the beam splits water molecules inside the cell, producing highly reactive fragments that attack DNA. Breaks through both strands at the same point are the lethal ones, because they are difficult to repair correctly. A damaged cell often survives until it next attempts to divide, and only then fails. That delay is why tumors shrink over the following weeks rather than during the session itself.
Why is treatment split into many small doses?
Normal tissue repairs radiation damage better and faster than tumor tissue does. Dividing the total into small daily amounts gives healthy cells the overnight gap they need to recover, while tumor cells, with their faulty repair, fall further behind after each session. Splitting the course also catches cells at different points in their cycle, since a cell is most vulnerable while dividing. The usual pattern is a short session each weekday for several weeks, although some treatments deliver a large amount in one or a few sessions to a very precisely mapped target.
How is it delivered?
| Approach | How the radiation reaches the tumor |
|---|---|
| External beam | A machine outside the body aims through the skin |
| Internal source | A sealed radioactive source placed in or beside the tumor |
| Systemic | A radioactive substance that collects in the target tissue |
Most treatment is external beam radiation therapy, shaped by movable leaves in the machine head so the high-dose region matches the outline of the tumor. Internal radiation therapy places the source within millimeters of the target, so the dose falls away steeply just outside it. Proton beam radiation therapy uses particles that stop at a set depth and release almost nothing beyond, which matters most when a sensitive structure lies immediately behind the tumor.
What side effects does it cause?
Effects follow the area treated, because radiation harms only what the beam passes through. Skin in the treated field reddens and can become sore, and tiredness builds through a course. Treatment of the head and neck brings a dry mouth and pain on swallowing; the abdomen brings nausea and loose stools; the pelvis affects bladder and bowel. Late effects appear months or years afterward and include scarring and stiffening of treated tissue, along with a small rise in the risk of a second cancer within the treated area.
Also known as
Used in a sentence
The plan called for radiotherapy to the breast in daily fractions over three weeks.
Good to know
Radiation affects only the tissue the beam passes through, so side effects follow the treated area rather than affecting the whole body as chemotherapy does.
Word origin
Where “radiotherapy” comes from
Radio- comes from the Latin radius, meaning a ray or spoke; therapy comes from the Greek therapeia, meaning healing or attendance.