Introduction - Prediction and Classification of Respiratory Motion - page 1

Chapter 1
Introduction
Rapid developments in radiotherapy systems open a new era for the treatment of
thoracic and abdominal tumors with accurate dosimetry [ 1 ]. For accurate treatment
planning and target motion acquisition, radiotherapy systems should take into
consideration not only technical limitations, but also physiological phenomena,
especially respiratory motion [ 1 , 2 ]. The delivery system cannot respond instan-
taneously to target position measurement since this measurement itself takes some
time. Target prediction method due to respiratory motion is proposed as a solution
to increase targeting precision before or during radiation treatments [ 1 , 3 ]. The
significant merit of predicting respiratory motion is that radiotherapy can be
delivered more accurately to target locations, reducing the volume of healthy
tissue receiving a high radiation dose [ 1 ]. The objective of this study is to deliver a
comprehensive review of current prediction methods for respiratory motion and
propose a new prediction method of respiratory motion.
Respiratory motion severely affects precise radiation dose delivery because
thoracic and abdominal tumors may change locations by as much as three centi-
meters during radiation treatment [ 3 - 5 ]. A number of methods to mitigate the
effect of respiratory motion are widely used in radiotherapy systems [ 1 ]. Respi-
ratory gating methods can deliver radiation treatment within a specific part of the
patient's breathing cycle (referred to as gate), where radiation is activated only
when the respiratory motion is within a predefined amplitude or phase level [ 2 , 6 ].
Breath-hold methods, exemplified by the deep inspiration breath hold, have been
prominently used for lung cancer radiotherapy, where the therapists may turn on
the beam only if the target breath-hold level is reached; otherwise, the treatment is
withheld [ 1 ].
Real-time tumor tracking is a more advanced technique to dynamically adjust
the radiation beam according to the change of tumor motion [ 1 ], where variations
in tumor motion caused by respiratory motion should be minimized with the
precise patient positioning system [ 7 ]. If the acquisition of tumor position and the
repositioning of the radiation beam are not well synchronized, a large volume of
healthy tissue may be irradiated unnecessarily and the tumor may be underdosed
[ 8 - 13 ]. There exists a finite time delay (or system latency) between measuring and
responding to real-time measurement [ 1 , 14 - 16 ]. Due to the magnitude of the