Why can high-energy megavoltage radiation treat tumors deep inside the body?

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linear accelerator; external beam radiation therapy — radiation therapy External beam radiation therapy (also known as external beam teletherapy, or long-distance therapy) being delivered using a machine known as a linear accelerator.

High-energy megavoltage radiation is effective for treating deep-seated tumors because its high energy level allows the radiation beam to penetrate through surface tissues to reach internal targets.1

In contrast to older orthovoltage X-rays (140–400 kilovolts), which deposited significant energy at the skin level and caused severe burns, megavoltage beams (exceeding 1,000 kilovolts) deliver a much lower dose to the skin. This "skin-sparing" effect, combined with the beam's ability to travel through the body to reach deep-seated growths, makes modern radiation therapy a safer and more precise tool for oncology. These beams are typically generated by linear accelerators that accelerate particles to produce the necessary therapeutic energy.1