Interpolation of tabulated proton Bragg peaks.

Treatment planning databases for pencil beam scanning can be large, difficult to manage and problematic for quality assurance when they contain tabulated Bragg peaks at small range resolution. Smaller range resolution, in the absence of an accurate interpolation method, improves the accuracy in dose calculations. In this work, we derive an approximate scaling function to interpolate between tabulated Bragg peaks, and determine the accuracy of this interpolation technique and the minimum number of tabulated peaks in a treatment planning database. With the new interpolation technique, three tabulated mono-energetic Bragg peaks (N = 3) are a suitable lower limit for N to achieve interpolation accuracy better than ±1% of the maximum dose in pristine and spread out Bragg peaks for ranges between 6.8 and 32.1 cm of water.