Pencil-Beam-Algorithmus

Der Pencil-Beam-Algorithmus ist eine von Bestrahlungsplanungssystemen in der Strahlentherapie genutzte Dosiskalkulationstechnik für der Strahlendosis im Gewebe.

The “pencil beam” algorithm is dose calculation technique. It assumes that any collimated photon beamhitting (incident) on the patient is actually a conglomeration of lots of smaller, narrow “pencil beams”.Each of these pencil beams has a central axis ray along which it deposits some dose. The dosedeposition pattern varies with the intensity and the spectrum of the beam that is incident on thepatient.

Pencil Beam Dose Calculation AlgorithmMartin G Carolan, PhDChief Physicist, Illawarra Cancer Care Centre10 Nov 2010 (Google Scholar)

Ausführlicher aber m.E: zu ausführlich deshalb Englisch belassen:

PB is a correction‐based algorithm in which dose calculation is performed on an infinitely narrow pencil beam dose distribution. Dose kernels are acquired within a homogeneous medium such as water to calculate the absorbed dose. The PB algorithm takes into account the inhomogeneity correction for the longitudinal direction in the central beam axis but ignores lateral scatter. This condition may cause dose calculation inaccuracies for heterogeneous treatment sites such as the lung or chest wall. A patient's body contains different densities, requiring a correction factor for each beam causing beam attenuation.² The PB algorithm is very fast due to its use of a one‐dimensional density correction, which does not accurately model the distribution of secondary electrons in heterogeneous media,³, ⁴ while its limitations in a heterogeneous medium are well known. The PB algorithm considers collimated photon beams incident on the patient as clusters of many small, narrow “pencil beams” each of which has central axis ray deposits with certain doses. The pattern of such dose deposits changes with the intensity and the beam spectrum incident on the patient.⁵

RADIATION ONCOLOGY PHYSICS Dosimetric comparison of pencil beam and Monte Carloalgorithms in conformal lung radiotherapy Yelda Elcim, Bahar Dirican, Omer Yavas

DOI: 10.1002/acm2.12426

Vorschlag Loose (ICRP 127):
A beam of radiant energy concentrated in an approximately conical or cylindrical portion of space of relatively small diameter. Pencil beam (algorithm) One of the dose calculation techniques for radiotherapy treatment planning. It assumes that any beam incidenting the patient is actually a conglomeration of lots of ‘pencil beams’, and the dose at any point of interest is given as the superposition of all the pencil beams. Pencil beam (in scanning irradiation technique) Dose is delivered by superposing ‘pencil beams’ from an accelerator on the target by controlling the beam path three-dimensionally.