Abstract
The purpose of the present work is to develop analytical expressions for the depth
variation of the fluence, planar fluence, the energy fluence, planar energy fluence,
the mean energy and absorbed dose of primary ions and their associated fragments in
tissue-like media with ranges of clinical interest. The analytical expressions of
the primary ions and associated fragments take into account nuclear interactions,
energy losses, range straggling and multiple scattering. The analytical models of
the radiation field quantities were compared with the results of the modified Monte
Carlo (MC) code SHIELD-HIT+. The results show that the shape of the depth absorbed dose distribution of the primary
particles is characterized by an increasingly steep exponential fluence decrease with
depth as the charge and atomic weight increase. This is accompanied by a compensating
increased energy loss towards the Bragg peak as the charge of the ion increases. These
largely compensating mechanisms are the main reason that the depth absorbed dose curve
of all light ions is surprisingly similar. In addition, a rather uniform dose in the
plateau region is obtained since the increasing fragment production almost precisely
compensates the loss of primaries. The dominating light fragments such as protons
and alpha particles are characterized by longer ranges than the primaries and their
depth dose curves to some extent coincide well with the depth fluence curves due to
a rather slow variation of mean stopping powers. In contrast, the heavier fragments
are characterized by the build up of a slowing down spectrum similar to that of the
primaries but with initially slightly shorter or longer ranges depending on their
mass to atomic number ratio. The presented analytical theory for the light ion penetration
in matter agree quite well with the MC and experimental data and may be very useful
for fast analytical calculations of quantities like mean energy, fluence, energy fluence,
absorbed dose, and LET.
Keywords
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Article info
Publication history
Published online: April 06, 2009
Accepted:
February 17,
2009
Received in revised form:
February 4,
2009
Received:
June 13,
2008
Identification
Copyright
© 2009 Associazione Italiana di Fisica Medica. Published by Elsevier Inc. All rights reserved.
