International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May-2013
ISSN 2278-7763
496
Effect of Change in Orientation of Enhanced Dynamic Wedges on
Radiotherapy Treatment Dose
Saeed Ahmad Buzdar1, M. Afzal Khan1, Aalia Nazir1, M. A. Gadhi2, Altaf H. Nizamani3, Hussain Saleem4
1
Department of Physics, The Islamia University of Bahawalpur, Pakistan
Department of Medical Physics, Bahawalpur Institute of Nuclear Medicine & Oncology (BINO), Bahawalpur, Pakistan
3
Department of Physics, University of Sind Jamshoro, Hyderabad, Pakistan
4
Department of Computer Science, University of Karachi, Karachi, Pakistan
2
Email:
saeed.buzdar@iub.edu.pk, afzalrao@hotmail.com,
hussainsaleem@uok.edu.pk (Corresponding Author)
alia.nazir@iub.edu.pk, asghargadhi@gmail.com, altaf_nizamani@yahoo.com,
ABSTRACT
Enhanced Dynamic Wedges are used in radiotherapy treatment to modify the dose distribution in target volume so that a desired dose distribution is achieved. The technique being highly advanced and computer controlled, requires enhanced degree of
quality assurance. The investigation aimed to verify the constancy of treatment dose, when the orientation of the enhanced dynamic wedge (EDW) is reversed. It has been noted that there is a slight change in the monitor units with the reversal of EDW
orientation. The calculated dose for two opposite orientations of EDW has been compared for 6 and 10 MV photon beams, by
two different calculation systems (Pencil Beam & Collapsed Cone) to assure the quality of EDW technique as well as to increase
its reliability. The difference in the calculated dose for Y1-IN and Y2-OUT orientation, for three different field sizes and all seven
wedge angels, is very small and hence not enough to change the wedge factor significantly.
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Keywords : Radiotherapy, Wedge Factor, Enhanced Dynamic Wedges, Radiotherapy, Quality Assurance
1
INTRODUCTION
W
EDGED fields are often used in radiation therapy
treatment by high-energy beams to modify the isodose
distribution by compensating dose inhomogeneity
[1],[2],[3],[4],[5],[6]. To improve the dose distribution, concept
of Static wedge has been extended to Dynamic wedge [7]
which is capable to make any wedge angle, by the movement
of one pair of independent jaws [8],[9],[10],[11] and resulting
in reduced attenuation and beam hardening effects [12],[13].
Enhanced Dynamic Wedges (EDW) offer many advantages
over conventional hard wedges for linear accelerator treatments. Along with these advantages the responsibility to deliver the correct dose is increased so that this complex technology is utilized to improve the treatment outcome. This involves determining the enhanced dynamic wedge factors for
various field sizes and depths for use in the hand calculation
of monitor units (MUs). The precise illustration of dynamic
wedges in the treatment planning computer necessarily also
be confirmed. This is required so that the final isodose distributions are correct and the MUs calculated by the treatment
planning computer match with those determined by hand
calculation [14],[15]. Different approaches have been followed
in order to address the quality assurance of EDW [16],[17],[18].
Modern radiotherapy practice motivates the development of
more modern and sophisticated approaches to assure quality
for our clinical radiotherapy treatment methods [19],[20]. This
work is an attempt to enhance the reliability of EDW commissioning by analyzing the dose calculation in two different
wedge orientations.
Copyright © 2013 SciResPub.
2
MATERIALS & METHODS
This investigation has been done for two photon energies 6
and 10 MV of Varian Linear Accelerators, for all seven Enhanced Dynamic wedges (EDWs) 100, 150, 200, 250, 300, 450,
600. The objective was to calculate the monitor units at normalization depth of 5 cm, for 95 cm SSD. (100 Monitor Units
were desired to be delivered at that depth). Treatment dose
has been calculated for three symmetric field sizes 4x4, 10x10
and 20x20 so that the effect will be noted on all three kinds of
the field sizes (the small, medium and large field). This practice has been repeated for all seven Enhanced Dynamic Wedges, and for both photon energies. Oncentra MasterPlan treatment planning system has been used for the dose calculation.
Oncentra Master Plan treatment planning system contains two
calculation algorithms Pencil Beam and Collapsed Cone Convolution. This diversity has been utilized to ensure the reliability of the calculations.
3.
OBSERVATIONS AND DISCUSSION
The treatment dose for two photon energies, for three field
sizes has been calculated and presented in tables and figures
below. These results are a comparison of two reverse orientations of same EDW, for same field size and photon energy.
Further a comparison of two calculation algorithms is also
presented. It helps to verify the difference in dose for two
wedge orientations. It can be seen that both pencil beam and
collapsed cone calculation algorithms are indicating almost
similar variation in dose when the EDW orientation is reversed from Y1 IN to Y2 OUT.
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International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May-2013
ISSN 2278-7763
497
TABLE 1: MONITOR UNITS FOR ALL EDW ANGLES, FOR TWO WEDGE ORIENTATION, CALCULATED FROM PENCIL BEAM AND COLLAPSED CONE
ALGORITHM. ENERGY OF BEAM 6 MV PHOTON AND THREE FIELD SIZES “4 X 4”, “10 X 10” AND “20 X 20”
6 MV Photon
Field Size (cm2)
4x4
EDW angle
(deg)
Y2 OUT
% DEV
Y1 IN
Y2 OUT
% DEV
10
111.47
111.39
-0.07
111.23
111.14
-0.08
15
112.36
112.24
-0.11
112.12
111.99
-0.12
20
113.3
113.14
-0.14
113.05
112.88
-0.15
25
114.3
114.09
-0.18
114.05
113.82
-0.20
30
115.38
115.12
-0.23
115.13
114.85
-0.24
45
119.51
119.04
-0.39
119.24
118.73
-0.43
60
126.65
125.79
-0.68
126.37
125.44
-0.74
105.21
105.22
0.01
104.96
104.97
0.01
107.93
107.94
0.01
107.67
107.69
0.02
110.78
110.80
0.02
110.51
110.54
0.03
113.81
113.84
0.03
113.52
113.56
0.04
30
117.09
117.13
0.03
116.79
116.84
0.04
45
129.55
129.62
0.05
129.18
129.28
0.08
60
150.95
151.08
0.09
150.47
150.67
0.13
10
105.73
105.74
0.01
106.96
106.98
0.02
15
112.45
112.48
0.03
113.76
113.79
0.03
20
119.47
119.51
0.03
120.86
120.90
0.03
25
126.93
126.98
0.04
128.40
128.45
0.04
30
134.98
135.05
0.05
136.54
136.61
0.05
45
165.32
165.45
0.08
167.18
167.32
0.08
60
216.61
216.92
0.14
219.00
219.33
0.15
15
20
20 x 20
Collapsed Cone
Y1 IN
10
10 x 10
Pencil Beam
25
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Copyright © 2013 SciResPub.
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International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May-2013
ISSN 2278-7763
498
TABLE 2: MONITOR UNITS FOR ALL EDW ANGLES, FOR TWO WEDGE ORIENTATION, CALCULATED FROM PENCIL BEAM AND COLLAPSED CONE
ALGORITHM. ENERGY OF BEAM 10 MV PHOTON AND THREE FIELD SIZES “4 X 4”, “10 X 10” AND “20 X 20”
10 MV Photon
Field Size (cm2)
4x4
EDW angle
(deg)
Y2 OUT
% DEV
Y1 IN
Y2 OUT
% DEV
10
109.85
109.86
0.01
110.07
110.08
0.01
15
110.58
110.58
0.00
110.8
110.8
0.00
20
111.34
111.35
0.01
111.56
111.57
0.01
25
112.15
112.16
0.01
112.37
112.38
0.01
30
113.03
113.04
0.01
113.25
113.26
0.01
45
116.38
116.39
0.01
116.59
116.62
0.03
60
122.16
122.19
0.02
122.37
122.42
0.04
104.34
104.35
0.01
104.11
104.13
0.02
106.59
106.6
0.01
106.35
106.37
0.02
108.94
108.96
0.02
108.69
108.72
0.03
111.44
111.47
0.03
111.18
111.22
0.04
30
114.15
114.19
0.04
113.88
113.93
0.04
45
124.44
124.51
0.06
124.13
124.21
0.06
60
142.2
142.27
0.05
141.74
141.91
0.12
10
104.55
104.57
0.02
105.32
105.34
0.02
15
109.96
109.98
0.02
110.77
110.79
0.02
20
115.61
115.65
0.03
116.46
116.49
0.03
25
121.61
121.66
0.04
122.5
122.55
0.04
30
128.1
128.16
0.05
129.03
129.1
0.05
45
152.59
152.72
0.09
153.68
153.81
0.08
60
194.3
194.5
0.10
195.57
195.85
0.14
15
20
20 x 20
Collapsed Cone
Y1 IN
10
10 x 10
Pencil Beam
25
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International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May-2013
ISSN 2278-7763
0.05%
499
0.00%
0
0.04%
10
20
30
40
50
60
70
-0.10%
-0.20%
0.03%
0.03%
PB
CC
0.02%
0.02%
0.01%
0.01%
Percentage deviation
Percentage Deviation
0.04%
-0.30%
PB
CC
-0.40%
-0.50%
-0.60%
0.00%
0
10
20
30
40
50
60
70
-0.01%
-0.70%
EDW (degree)
-0.80%
Fig-1: Percentage deviation between the doses for two EDW
2
Orientations, for 10 MV Photon and 4x4 cm Field Size
EDW (degree)
Fig-4: Y1 IN & Y2 OUT Percent deviation in MUs, for 6 MV
2
Photon and 4x4 cm Field Size
0.14%
0.14%
0.12%
0.10%
0.08%
0.10%
0.08%
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CC
PB
0.06%
Percentage deviation
Percentage deviation
0.12%
PB
CC
0.06%
0.04%
0.04%
0.02%
0.02%
0.00%
0.00%
0
10
20
30
40
50
60
0
70
10
20
30
40
50
60
70
EDW (degree)
EDW (degree)
Fig-2: Y1 IN & Y2 OUT Percent deviation in MUs, for 10 MV
2
Photon and 10x10 cm Field Size
Fig-5: Y1 IN & Y2 OUT Percent deviation in MUs, for 6 MV
2
Photon and 10x10 cm Field Size
0.16%
0.16%
0.14%
0.14%
Percentage deviation
0.10%
PB
CC
0.08%
0.06%
Percentage deviation
0.12%
0.12%
0.10%
PB
CC
0.08%
0.06%
0.04%
0.04%
0.02%
0.02%
0.00%
0
0.00%
0
10
20
30
40
50
60
70
EDW (degree)
Fig-3: Y1 IN & Y2 OUT Percent deviation in MUs, for 10 MV
2
Photon and 20x20 cm Field Size
Copyright © 2013 SciResPub.
10
20
30
40
50
60
70
EDW (degree)
Fig-6: Y1 IN & Y2 OUT Percent deviation in MUs, for 6 MV
2
Photon and 20x20 cm Field Size
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International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May-2013
ISSN 2278-7763
Table-1 and Table-2 present the data sets obtained for the
monitor units (MUs) calculated, when dose was normalized
on a depth of 5 cm, with 95 cm SSD (100 MUs on this depth).
These tables contain the information for change in the dose for
two different orientation of EDW, for field sizes 4x4, 10x10 and
20x20, for each photon energy 6 and 10 MV. Additionally, all
the exploration has been done for both the calculation systems
integrated with Oncentra MasterPlan Treatment Planning System; the Pencil Beam and Collapsed Cone Convolution. This
similar kind of deviation between doses for two opposite orientation, confirmed by both the calculation algorithms, indicates reliability of the results. The percentage deviation between monitor units calculated for two opposite orientations
have been plotted against wedge angles, for three field sizes
and both photon energies, are represented below in Fig-1 to
Fig-6. The dotted curve is deviation obtained by Pencil Beam
algorithm while solid line representing the calculations made
through Collapsed Cone Convolution algorithm.
The percentage deviation between two doses, for two opposite orientations of EDW, for three different field sizes, is
graphically represented in figure 1 to figure 6. Percent Deviation seems to increase with increasing wedge angle. The maximum percentage difference is -0.68 for 6 MV calculated by
Pencil beam, and -0.74 for Collapsed Cone calculations. While
this difference is remarkably small for 10 MV, the maximum
deviation is 0.10 % for Pencil beam calculations, and 0.12 % for
Collapsed Cone. The overall results are within 1 % deviation.
This constancy enhances the reliability of the EDW to be used
for modification of the dose distribution.
The change in the dose, due to change in the wedge orientation, needs to be further investigated. Lots of experiments
have been done to study the role, effectiveness and procedures
of Enhance Dynamic wedges, but this thing need to be explored too. Even this change is not too big to effect the treatment planning, but it needs to be optimized to ensure that this
is not some inaccuracy of the dose calculation system.
500
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4 CONCLUSION
The effect on treatment dose due to change in the orientation
of EDW (from Y1 IN to Y2 OUT) has been analyzed and it is
found that there is a slight change in the dose by reversing the
wedge orientation but this is not enough to change the wedge
factors significantly. The constancy in the monitor unit calculation is verified to assure the quality of Enhanced Dynamic
Wedges.
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for 25 V X-rays”, Radiology, 136,757-762; 1980.
Copyright © 2013 SciResPub.
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International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May-2013
ISSN 2278-7763
Saeed Ahmad Buzdar is presently an Assistant
Professor in the Department of Physics, The
Islamia University of Bahawalpur. He has completed his Ph.D in Medical Physics from the
Islamia University Bahawalpur, Pakistan. Recently he is a Post Doc Fellow at University
College London, U.K. He is also associated with
Medical Physics Research Group at the Islamia
University Bahawalpur, Pakistan. His areas of
interests are Medical Physics, Physics of Radiation Therapy, Physics of Medical Imaging, Computational Physics, and
Radiation Dosimetry.
Muhammad Afzal Khan is Professor at Department of Physics, The Islamia University
Bahawalpur, Pakistan. He got associated there
since 1983. He started research in collaboration
with Department of Medical Physics at
Ninewells Hospital & Medical School, University of Dundee, UK in 1995 and had conducted
research in MR Imaging with hospital service
work in diagnostic radiology and radiotherapy
of cancer. He was awarded Ph.D in 1998. On his
return, he took up various academic assignments and continued his research in Medical Physics. He has worked closely with Bahawalpur Institute of Nuclear Medicine and Oncology (BINO-Cancer Hospital of Pakistan Atomic Energy Commission) and Quaid-e-Azam Medical College,
Bhawalpur to complete more than twenty research projects.
501
Hussain Saleem is Assistant Professor and Ph.D.
Research Scholar at Department of Computer
Science, University of Karachi, Pakistan. He received B.S. in Electronics Engineering from Sir
Syed University of Engineering & Technology,
Karachi in 1997 and has done Masters in Computer Science from University of Karachi in 2001.
He also received Diploma in Statistics from University of Karachi in 2007. He bears vast experience of more than 16 years of University Teaching, Administration and Research in various dimensions of Computer
Science. Hussain is the Senior Instructor and has been associated with the
Physics Labs at Aga Khan Ex. Students Association Karachi since 1992. He
served as Bio-Medical Engineer at Aga Khan University in 1999-2000,
where he practiced to handle Radiology and MRI equipments. Hussain is
the Author of several International Journal publications. His field of interest is Software Science, System Automation, Hardware Design & Engineering, Data Analysis, and Simulation & Modeling. He is senior member
of Pakistan Engineering Council (PEC).
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Aalia Nazir has completed Ph.D. in Medical
Physics from The Islamia University, Bahawalpur, Pakistan in 2011. During her studies she
had conducted research at University of Dundee
Scotland UK. Her areas of interests are Medical
Physics, Physics of Radiation Therapy, Physics
of Medical Imaging, Computational Physics,
Radiation, Dosimetry, Radiology, Magnetic Resonance Imaging (MRI), Gel Dosimetry and use
of Nanotechnology for the treatment of cancer.
Muhammad Asghar Gadhi is a Medical Physicist at the Department of Medical Physics, Bahawalpur Institute of Nuclear Medicine & Oncology (BINO), Bahawalpur, Pakistan. He received M.Phil. in Medical Physics in 2007 from
The Islamia University of Bahawalpur, Pakistan.
His areas of interests are Medical Physics, Physics of Radiation Therapy, Physics of Medical
Imaging, Computational Physics, and Radiation
Dosimetry.
Altaf Hussain Nizamani is working as Assistant
Professor at the Institute of Physics, University
of Sindh, Jamshoro, Pakistan. He received Ph.D
degree in Ion-Trapping and Quantum computation technology from the University of Sussex,
Brighton, UK in 2011. His areas of interests are
Scalable Ion trap chips for the quantum computing and information technology, ultra high vacuum system designing, FPGA and Real-time
LabVIEW programming, LASER cooling & trapping and computational Physics.
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