How Does Radiotherapy Work?

What is Radiotherapy?

In oncology, radiotherapy is a specific type of cancer treatment, used alone or in combination with other treatments such as surgery and chemotherapy. It uses radiation, generally X-rays (ionizing radiation), to fight tumors. This is the same type of radiation used in X-rays and CT scans, emitted by radioactive substances like iodine or cobalt, or produced by linear accelerators.

How Does a Radiotherapy Session Proceed?

External Radiotherapy

In external radiotherapy, the radiation source is outside the body. The device is painless and doesn't touch the body, directing rays to the tumor. It's generally outpatient; you go to the hospital for treatment and return home afterward.

Internal Radiotherapy

This administers radiation from inside the body. Methods include tiny radioactive probes placed near the tumor, or a radioactive liquid drunk or injected intravenously and absorbed by tumor cells. Internal radiotherapy often requires (usually short-term) hospitalization. Brachytherapy involves placing radioactive sources directly in or near the tumor.

Interstitial brachytherapy uses a small surgical procedure to insert tiny radioactive metal probes into the tumor. Local or general anesthesia may be needed. The source remains in the body for a set time – minutes to days – before removal. In some cancers (e.g., some prostate cancers), the source remains permanently. Small radioactive seeds are implanted and release radiation progressively, mostly contained within the tumor area. The patient doesn't emit significant radioactivity and poses no danger to others, though avoiding close contact with children and pregnant women is generally advisable for a period depending on the substance used. In rare cases of detectable external radioactivity, longer hospitalization may be needed to prevent contact until radioactivity dissipates.

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How Does Radiation Reach the Target?

Radiation is Directed at the Tumor

Radiation targets the tumor to damage cancer cells, preventing proliferation and potentially shrinking the tumor. Radiation reaches the target through:

• External radiotherapy (or transcutaneous, or external beam): the radiation source is outside the body;
• Internal radiotherapy: administered from inside the body, using methods described above;

Destruction of Tumor Cells

Radiotherapy selectively ionizes tissues using high-energy radiation beams. Ionization creates ions and free radicals that damage cells. This damage to DNA, proteins, and lipids leads to cell death, achieving biological inactivation of the targeted tissue.

Radiation Dosage

Radiation dose is measured in grays (Gy). The Sievert (Sv) considers both energy deposited and biological effectiveness.

Can Radiation Damage Nearby Healthy Tissues?

While modern radiotherapy is precise, nearby healthy cells may be affected, causing side effects. However, healthy cells repair damage better than tumor cells, making radiotherapy effective with generally limited side effects.

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