Figure 15.
Absorbed dose D as a function of depth z in water from a spread-out Bragg peak (SOBP) (uppermost curve) and its constituent pristine Bragg peaks (lower curves; for clarity, all but the deepest pristine Bragg peak are only partly drawn). In many cases, the clinical target volume is larger than the width of a pristine Bragg peak. By appropriately modulating the proton range and fluence of pristine peaks, the extent of the high-dose region can be widened to cover the target volume with a uniform dose.