Biomedical Engineering Reference
In-Depth Information
Chapter 18
Track-Structure Monte Carlo Modelling
in X-ray and Megavoltage Photon Radiotherapy
Richard P. Hugtenburg
Abstract
The use of track structure calculations in radiotherapy using conventional
low-LET radiation sources is discussed. Microdosimetry and emergent nanodosime-
try methods are considered in explaining variations in quality factors associated with
clinical practice and in vitro data. Transformation rate in the human derived for the
in vitro system CGL1 is presented as a model for the induction of secondary cancer,
a late effect associated with radiotherapy treatment.
18.1
Introduction
The use of radiation in cancer therapy is highly developed and has been shown
to be successful only with high orders of accuracy [
1
]. The principal measure
of radiation efficacy is the absorbed dose, however an increasingly wide variety
of radiation sources are now used in radiotherapy and the assumption that the
clinical response is dependent only on the absorbed dose is inaccurate in many
cases. Despite the advantages of new modalities, including better normal tissue
sparing, and less sensitivity to oxygenation effects, e.g. from ion-beam therapy or
biological targeting, it is likely that similar, high orders of accuracy are needed in
the determination of effective dose.
Physical models that go beyond the fundamental quantity of dose are increasingly
being used in radiation therapy in order to better understand and to optimally design
treatments. This has been driven by the adoption of new modalities, such as ion-
beam therapy and boron neutron-capture therapy, where corrections to the dose to
determine clinical efficacy are substantial. These models utilise models based on
calculated linear energy transfer (LET) or microdosimetric quantities such as the
