Development and test of a respiration gated system in
radiotherapy : work in progress
1Jin-Bum
Chung, 2Won-Kyun Chung, 1Tae-Suk Suh, 1Kyoung-Sick Choi
1
Department of biomedical Engineering , College of Medicine, Catholic University , Seoul, Korea
2
Department of Radiation Sciences, Seoul Health College, Sungnam, Korea
Abstract
The measurement of respiratory pattern will be performed with the sensor system such as strain gauge and spirometer. The
measured data will be analyzed and estimated from day to day in order to show variation of respiratory patterns with following
period and amplitude variation vs. Time. A test will be performed the measurement of respiratory pattern in order compare the
measured values with/without immobilization device with sensor system and with/without immobilization device which developed by
us.
Keywords
Respiation gated raiotherapy, respiatory, respiration pattern, strain gauge, spriometer
Introduction
In cancer radiotherapy, one of the most important points is to
concentrate a uniform prescribed dose to the target volume
while minimizing irradiation to surrounding normal tissues. In
this regard, many techniques such as fractional stereotactic
radiotherapy, 3D comforaml radiotherapy and IMRT are used
for cancer treatment.
In therapy of lung or liver cancer that moves along with the
respiration, the large margin around the clinical target volume
is expanded so as to always irradiate it during motion. This
increase the irradiated volume of the normal tissue. To
concentrate the dose to a moving target, two kinds of methods
have been proposed to reduce effect of respiratory motion. One
is to control the target motion by keeping the breath of the
patient artificially paused during irradiation. The other is to
irraditate the beam on a moving target along with the patient
respiratory motion(1,2,6). In the latter method, patient
movement during treatment must be minimize in order to
optimize external-beam. The pupose of our study is also to
development a gating tool in order to imitate the pattern of the
breath cycle and to control target motion. It will help to reduce
the plannig target volume(PTV) and provide accurate delivery
of the prescrived dose to the target.
In the past several years, John. W. Wong et al., at the
William Beaumont Hospital, has developed an active breahting
control(ABC) method to reduce margin for breathing
motion(4). This technique has been explored as a possible
treatment for a variety of tumors. It has been shown to be a
reproducible method of controlling patient breathing through
the use of an occlusion value at a specified level in the
respiratory cycle. Hanley et al., at the Memorial SloanKettering Cancer Center, published their first paper in 1996.
Their method is strictly based on a deep inspiration breath-hold
technique(5). There are several institutions in North America
that are pursuing their own programs.
In this paper, we investigated respiration gated system used
in radiotherapy, and deals with the measurement of breathing
patterns from the synchronized signal using sensor system such
as strain gauge and spiromter during patient’s respiration. We
will report working and progress regarding this system in
future study.
Material and methods
Our research objective is to study the temporal
characteristics of the respiraiton cycle during breathing and to
measure real dose distrbution in a moving target. In order to
achieve this goal, we are currently at the stage of designing and
fabricating a respiration-gated system which consists of a few
respiratory sensors such as strain gauge and spirometer, and a
signal processing module including amplifier, electronic logic
modules and ADC. A strain gauge and spirometer are chosen
so as to satisfy sensor conditions such as reliability, accuracy,
quick response, reproducibility, convenience. For example,
strain gauge signals are related to the degree of body motion
and increase with increasing body displacement. Also, the
spirometer is used to measure lung capacity by measuring the
volume of air passing through the airway during respiration.
Both sensors are simultaneously measured and compared under
the same condition and for the same patient. Signal processing
modlue has the function of amplifying the weak signal from the
sensors, measuring and deciding the right level of gated cycle,
and producing the appropriate gate signal to the linac. For the
measurement of the dose distribution in a moving target, a
moving phantom is being constructed which moves
synchronously to the respiration cylce and contains the
dosimeters such as semiconductor detector and TLD. For our
reasearch project, we test the respiratory sensors on the moving
phantom and the patient, produce accurate and simulated
motion pulses, and process the signal to decide the optimized
gate level for controlling the linac beam output.
Results
In measurement of sensor system, strain gauge and
spirometer may produce the synchronized pulse cycles to the
respiration cycles. We exam the possible error and deviation
between these two pulses and obtain the correlation between
the position of the moving target and the produced pulse cycle.
This means to produce the exact simulation outputs from the
body motion and respiratory motion.
First, a test will be performed in order to observe the
breathing pattern including amplitude variation of the
repiratory pulses vs. time, the scope of time duraiotn of each
respiratory stage. This result show us which portion of the
respiratory cycle may be used to gate the beam output.
Second, the measured data from the sensors will be analyzed
using signal process modules so that accurate gating level may
be decide, and a possible relation between two sensors or if any,
other sensors may be obtained from the time information of the
signals from the tested sensors. This implies that we may use
many sensors simutaneously to produce the gate signal, not just
one sensor each time.
Third, actual dose distrbution will be measured from the
moving phantom when exposed to the linac beam output.
Result may be obtain from the experimental condition of both
no gating and gating to the linac veto input. This result will
give us a huge difference in dose distribution and at the same
time how long it takes for the gated beam to give the same dose
to the target compared to the ungated beam.
Fourth, a test will be performed for the measurement of
respiratory pattern with or without immobilization device
developed by our group previously. Measured data could be
compared under the condition with or without immobilization
device with the patient in.
Discussion and conclusion
A respiration gated system is under construction using many
electronic sensors, signal processing modules, and a moving
phantom. Many tests are outlined and ready to perform when
the system is completed. Our goal is to pursue the similar result
from other groups and possibly expand the use of the gated
technique in radiotherapy from the our custom made signal
processing modules and moving phantom. From the experience
of the radiation therapy, we have a confidence that the gated
technique in radiaion therapy will be further developed and
expanded for 3D conformal therapy and IMRT.
References
[1] Ohara K, Okumura T, Akisada M et al., 1989 Irradiation
synchronized with respiration gate. Int J Radiat Oncol Biol
Phys 17 853-857
[2] Kubo HD. Hill BC. 1996 Respiration gated radiotherapy
treatment: A thechnical study. Phys Med Biol 41 83-91
[3] J. W. Wong et al., 1999 The use of active breathing control
to reduce margin for breathing motion, Int. J. Radiat. Oncol.,
Biol., Phys. 44 911-919
[4] J. Hanley et al., 1996 Use of breath-hold helical CT and
spirometry in conformal radiotherapy treatment planning,
Radiology 201 406
[5] Cihat Ozahasoglu and Martin J. Murphy 2002 Issues in
respiratory motion compensation during external-beam
radiotherapy Int J Radiat Oncol Biol Phys 52 1389-1399
[6] Kubo HD et al., 2000 Breathing-synchronized radiotherapy
program at the University of California Davis Cancer
Center Med. Phys. 27 346-353