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What happens at the Bragg peak in proton beam therapy?
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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.
In proton beam therapy, the Bragg peak represents a specific point at the end of a particle's trajectory where it deposits a sharp maximum of energy.12
As protons travel through the body, they lose their residual energy over a very short distance, resulting in a steep rise in the absorbed radiation dose. This phenomenon is characterized by the following:1
- Energy Deposition: The ionization density—the number of ions produced per unit of path length—reaches its highest point at this peak.2
- Dose Distribution: Unlike photon radiation, which passes through the body, proton beams exhibit a lower dose in the tissue proximal to the tumor, a high and uniform dose at the tumor site, and a rapid falloff to zero dose beyond the peak.1
- Clinical Advantage: Because there is virtually no exit dose beyond the Bragg peak, this therapy is highly effective for treating tumors located near critical structures, such as the spinal cord, as it minimizes damage to surrounding healthy tissue.1
While the peak is naturally narrow, it can be spread out to cover the entire volume of a tumor.1