BraggPeak

BraggPeak refers to the pronounced maximum in the depth-dose distribution of charged-particle beams as they travel through matter, most evident in water-equivalent tissue. As protons or heavier ions slow down, they deposit most of their energy toward the end of their range, producing a peak in dose at a specific depth known as the Bragg peak.

Cause: Energy loss increases as velocity decreases (Bethe-Bloch theory), leading to high linear energy transfer near the end of the particle’s range. This accumulation of energy deposition creates the distinctive peak in dose at a finite depth.

Applications: In proton therapy and carbon ion radiotherapy, the Bragg peak allows a high dose to the tumor with reduced exit dose beyond it. To treat extended tumor volumes, practitioners create a spread-out Bragg peak (SOBP) by varying beam energy or using multiple beams, producing a uniform dose over the target while preserving distal sparing.

Limitations: Range uncertainties arise from tissue density variations, patient setup, and motion. Delivery systems require precise calibration, and range verification imaging is often used to ensure the peak aligns with the tumor.

History: The Bragg peak concept emerged from early investigations into energy loss and ionization by charged particles in the early 20th century, with the Bragg family among those whose work contributed to understanding depth-dose behavior. The feature has since become central to modern charged-particle radiotherapy, where its controlled placement enables targeted tumor irradiation with minimized damage to surrounding tissue.