Experimental characterization of two-dimensional pencil beam scanning proton spot profiles.

Abstract:

:Dose calculations of pencil beam scanning treatment plans rely on the accuracy of proton spot profiles; not only the primary component but also the broad tail components. Four films are placed at several locations in air and multiple depths in Solidwater® for six selected energies. The films used for the primary components are exposed to 50-200 MU to avoid saturation; the films used for the tail components are exposed to 800, 8000 and 80,000 MU. By applying a pair/magnification method and merging these data, dose kernels down to 10(-4) of the central spot dose can be generated. From these kernels one can calculate the dose-per-MU for different field sizes and shapes. Measurements agree within 1% of dose-kernel-based calculations for output versus field size comparisons. Asymmetric, comet-shaped profile tails have a bigger impact at superficial depths and low energies: the output difference between two orientations at the surface of a rectangular field of 40 mm×200 mm is about 2% at the isocentre at 100 MeV. Integration of these dose kernels from 0 to 40 mm radius shows that the charge deficit in the Bragg peak chamber varies <2% from entrance to the end of range for energies <180 MeV, but exceeds 5% at 225 MeV.

journal_name

Phys Med Biol

authors

Lin L,Ainsley CG,McDonough JE

doi

10.1088/0031-9155/58/17/6193

subject

Has Abstract

pub_date

2013-09-07 00:00:00

pages

6193-204

issue

17

eissn

0031-9155

issn

1361-6560

journal_volume

58

pub_type

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