1. Gunasekaran L.1,2
, Block A.1
, Zakaria G.A.2,3
1
Institute for Medical Radiation Physics and Radiation Protection, Klinikum, Dortmund, Germany.
2
HS-Anhalt University of Applied Sciences, Biomedical and Clinical Engineering, Koethen, Germany.
3
Gummersbach Hospital, Department of Radiation Physics, Gummersbach, Germany.
We are grateful to Rainer Bauer and Andreas Mewes for technical assistance.
Introduction
Respiratory and cardiac motions in the thoracic and abdominal
region induce displacement of the tumour volume as well as
various internal organs during the treatment. Amplitude, period
and other motion parameters shows wide variations, there are
no basic patterns, they are patient-specific. This experimental
study is to analyze the influence of the amplitude and the
phases of irregular tumour motion on dose distribution inorder to
find an effective dosimetric margins.
Materials and Methods
Equipment:
Therapy simulator: Acuity (Fa. Varian)
Linear Accelerator: Clinac 2100 C/D (Fa. Varian)
Triggering Unit: RPM-System (Fa. Varian)
CT: Light Speed (Fa. GE)
The patient's respiratory signal and target motion was recorded
for about 36 sec from the therapy simulator.
Analysis Software: ORAT
Organ Respiration Analysis Tool
The captured images of the respiratory signal and the target
motion is analyzed and marked in every frame by in-house
developed software ORAT and converted as different motion
patterns with different parameters.
Device to measure the 2D dose distribution:
MotionSim-2
MapCHECK XY/4D™ table (Sun Nuclear
Corporation)
The marked patterns are Tumour upper and lower edge and
Diaphragm lower and upper edge. Also the motion curves are
designed with different parameters like PERIODIC,BASELINE
SHIFT,CONSTANT AMPLITUDE with VARIABLE PERIODS
and CONSTANT PERIOD with VARIABLE AMPLITUDES.Then
the data's are given as input to 4DXY simulation table which
can track the tumour to simulate and traject the patient's
respiration with the supporting Motion Sim software. Then the
measurement was taken on Saturn-43 CLINAC with a diode
array device MAPCHECK-2 on top of the 4DXY motion table
which acts as a motion phantom and the measurements are
taken under the field size 10cmsX10cms with response to the
motion of the tumour and in rest positions and analyzed by
supporting software SNC Patient.
Media-Window for fluoroscopy
Cine-CT and cine-EPID
amplitude
frequency
respiratory amplitude
(red)
organ amplitude
(blue)
Radiooncologist
marks with
Crosshair
anatmomic
structure
Physicist
analyses the
Waveforms,
assesses
margin
Media-Window for fluoroscopy
Cine-CT and cine-EPID
Media-Window for fluoroscopy
Cine-CT and cine-EPID
amplitude
frequency
respiratory amplitude
(red)
organ amplitude
(blue)
Radiooncologist
marks with
Crosshair
anatmomic
structure
Physicist
analyses the
Waveforms,
assesses
margin
Influence of the amplitude and the phase due to respiratory
motion on dose distributions in Radiotherapy.
References
[1] S. S. Vedam, P. J. Keall, V. R. Kini, R. Mohan: Determining parameters for respiration-gated radiotherapy; Med. Phys. 28 (10), 2139 - 2146 (2001)
[2] L. I. Cerviño, A. K. Y. Chao, A. Sandhu and S. B. Jiang: The diaphragm as an anatomic surrogate for lung tumor motion, Phys. Med. Biol. 54 (2009) 3529–3541
[3] P. J. Keall, G. S. Mageras, J. M. Balter et al: The management of respiratory motion in radiation oncology report of AAPM Task Group 76; Med. Phys. 2006; 33:3874-3900
[4] A. Block, R. Bauer: Ein Auswerteprogramm zur visuellen und quantitativen Erfassung der intrafraktionellen Organbewegung; Med. Physik 2004, 342-343
[5] J. Lenz: Dosimetrische Messungen an bewegten Targets mit einem halbleiter-basierten 2D-Array, Diplomarbeit, TU Dortmund/ Institut für Medizinische Strahlenphysik und
Strahlenschutz am Klinikum Dortmund, 2012
[6] E. Becker: Dosimetrische Messungen in der Hochvolt-Strahlentherapie an bewegten Targets unter Einfluss der Wahl des Gatingfensters auf die 2-dimensionale Dosisverteilung,
Bachelorarbeit, Fachhochschule Münster/ Institut für Medizinische Strahlenphysik und Strahlenschutz am Klinikum Dortmund, 2012, S.10-25.
CONTACT: a.block@t-online.de
Analysis
Margin concept by The British Institute of Radiology.
Referring to the report:
"Geometric Uncertainties in Radiotherapy"
ri = 2.5 Σi + bi + β(σi - σp )
ri: semi-diameter of the ith principal axis
bi: breathing amplitude of the ith principal axis
Σi: standard deviation of systematic errors o f the ith principal
axis
σi: standard deviation of treatment execution errors
of the ith principal axis
β: 1.64 for cranio-caudal direction
σp: standard deviation of unblurred beam penumbra width.
Irregular motion patterns under isodose area.
Vedam et al. [1] were the first who proposed the idea those
lung tumors in the vicinity of the diaphragm move with the
same magnitude and phase as the diaphragm. This concept
was adapted of other groups [2]. Incase of deriving a margin,
the usage of diaphragm motions as a representative for tumour
motions seems to be difficult as the amplitude of the diaphragm
motions are twice larger than the tumour motion.
Different patients with different amplitudes &
periods.
Increasing amplitude can be correlated with increasing
influence on dose distributions, in other words increasing
shrinkage of 90%-isodose areas and increasing broadening of
10%-isodose areas.
Discussion
The problem of accounting the geometric uncertainities in radiotherapy is commonly addressed by drawing margins around the clinical target
volume. After a deep analysis on all concepts in this field, we found the Margin concept by BIR is better than the others as they cover all
possible uncertainies. When introducing respiratory patterns to the calculation of dosimetry margins, the amplitude of the respiratory cycle
and its time dependence have been assumed as the most important parameters. While these relations have been thoroughly examined in the
literature, considerably less attention has been paid on the phase of the respiratory pattern, which also varies with time. According to the
report of AAPM Task Group 76 [3] amplitudes can vary from a couple of millimetres to a few centimetres. In this work, we start by analysing
the influence of the respiratory amplitude of both, tumour and diaphragm, on the dose distribution and subsequently expand our enquiries
towards influence of the periods. As per our results, variable periods induce a stronger influence on isodose dimensions in the direction of
motion than any other parameter of derived periodic motions. Our research indicates that the phase of the respiratory cycle have great
influences on dosimetry margins. To calculate an effective margin for an individual patient tumour a precise investigation of the respiratory
pattern is necessary and the amplitude, phases and also its standard deviation should be paid more attention.
Results
Motion pattern with different parametric conditions
The derivated periodic motion influences two-dimensional dose
distribution more than the original irregular motion does. This is
important as periodic motions are chosen as representative for patient
patterns which is not adequate according to the current data. The
constant amplitude with variable periods have more influence than the
constant periods with variable amplitude.
Different motion patterns under standard deviation.
The irregularity can be expressed in terms of standard deviations. The
standard deviation of the breathing phases is ten times higher then the
standard deviations of the amplitude. Therefore varying periods induce
a stronger influence on isodose dimensions in the direction of motion
than any other parameter of derived periodic motions.