Calculation of a pencil beam kernel from measured photon beam data

Abstract

Usually, pencil beam kernels for photon beam calculations are obtained by Monte Carlo calculations. In this paper, we present a method to derive a pencil beam kernel from measured beam data, i.e. central axis depth doses, phantom scatter factors and off-axis ratios. These data are usually available in a radiotherapy planning system. The differences from other similar works are: (a) the central part of the pencil beam is derived from the measured penumbra of large fields and (b) the dependence of the primary photon fluence on the depth caused by beam hardening in the phantom is taken into account. The calculated pencil beam will evidently be influenced by the methods and instruments used for measurement of the basic data set. This is of particular importance for an accurate prediction of the absorbed dose delivered by small fields. Comparisons with measurements show that the accuracy of the calculated dose distributions fits well in a 2% error interval in the open part of the field, and in a 2 mm isodose shift in the penumbra region.

Performance of dose calculation algorithms from three generations in lung SBRT: comparison with full Monte Carlo‐based dose distributions

“…The output factor measurement results were daisy‐chained, as presented by Dieterich et al (24) The PBC algorithm is an analytical correction‐based algorithm where the dose is calculated by convoluting the field intensity fluence with narrow pencil beam kernels. Subsequently, corrections for patient surface obliquity and heterogeneities are performed 25 , 26 , 27 . The AAA is a semi‐analytical, model‐based algorithm, although its core is built on exploiting pencil beams.…”

Dosimetric verification of the anisotropic analytical algorithm for radiotherapy treatment planning

“…Dose calculations were performed using version 7.5.18 of the Eclipse Dose Calculation Server, using a 2.5mm calculation grid. Calculations performed with the system's older Pencil Beam Convolution algorithm [23] for comparison used the same grid size and an Equivalent Tissue-Air Ratio (ETAR) inhomogeneity correction, in line with current practice at our institution.…”

A system for intensity modulated dose plan verification based on an experimental pencil beam kernel obtained by deconvolution

“…This has been carried out by two different groups. 9,[15][16][17][18][19] They fitted the polyenergetic pencil beam kernel to an analytical expression according to experimental data usually measured during the commissioning procedure.…”