FIGURE 1.

(A) Molecular weight, (B) Physical property, (C) Organs at risk. Bragg peak principle: When a high‐speed charged particle passes through a material, the incident‐heavy ion gradually loses energy and eventually stops. The energy loss peaks immediately before the heavy ion beam stops and quickly approaches zero. This maximum range is named the spread‐out of the Bragg peak after its discoverer. The ionization density of the X‐rays increases until it reaches its maximum value; thus, the energy remains constant after passing through the target material.