The research about the effect of carbon fiber on cobalt-60 teletherapy type GWXJ80 to the depth dose when gamma rays passed the carbon fiber couch and its effect to the surface dose has been conducted. Depth dose has been measured using ionization detector 0.65cc Extradin A12 model with the buildup cup that is connected to the electrometer Max4000 (Standard Imaging). Depth dose data have been obtained from 5 cm, 6 cm, 7 cm and 9 cm of depth with angle variations of each depth are from 0o - 360o (10o angle interval ). The result of measurement has been processed using TRS398 protocol. The Surface dose measurement were performed using Gafchromic EBT2 film which was placed on the surface of slab phantom with and without carbon fiber. Irradiation field of this measurement were 6x6cm2, 8x8cm2, 10x10cm2, 12x12cm2, 14x14cm2, 16x16cm2 and 18x18cm2. The reading results of optic density using X-RITE densitometer were converted to dose refering the characteristic curve graph of Gafchromic EBT2 that had been prepared. Characteristic curve of the film have been made by giving 25cGy, 50cGy, 100cGy, 150cGy, 200cGy, 250cGy and 300cGy of dose to film strip in 2,5x3cm2 of field. The result of this research showed that in 5cm, 6cm, 7cm, 8cm and 9cm of the depth, can be obtained transmission factors 0.954, 0.952, 0.951, 0.950 and 0.948. A great transmission factor change occured at the gantry angle position at 100o to 120o. Carbon fiber application for the surface dose increased the relative dose from 10.9% into 37.4% (6x6cm2), 16.9% into 48.39% (8x8cm2), 23.0% into 63.3% (10x10cm2), 29.2% into 75.4% (12x12cm2), 33.3% into 80.1% (14x14cm2), 37% into 86.9% (16x16cm2) and 43.3% into 91.2% (18x18cm2).

1. International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
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Analysis of the Effect of carbon fiber utilization on Cobalt-
60 Teletherapy to the depth dose and the surface dose
Muhtarom*
Master Student
Department of Physics
Diponegoro University Semarang,
Indonesia
Eko Hidayanto
Department of Physics
Diponegoro University Semarang,
Indonesia
Heri Sutanto
Department of Physics
Diponegoro University Semarang,
Indonesia
Abstract-- The research about the effect of carbon fiber on cobalt-60 teletherapy type GWXJ80 to the depth dose
when gamma rays passed the carbon fiber couch and its effect to the surface dose has been conducted. Depth dose has
been measured using ionization detector 0.65cc Extradin A12 model with the buildup cup that is connected to the
electrometer Max4000 (Standard Imaging). Depth dose data have been obtained from 5 cm, 6 cm, 7 cm and 9 cm of
depth with angle variations of each depth are from 0o
- 360o
(10o
angle interval ). The result of measurement has been
processed using TRS398 protocol. The Surface dose measurement were performed using Gafchromic EBT2 film
which was placed on the surface of slab phantom with and without carbon fiber. Irradiation field of this measurement
were 6x6cm2
, 8x8cm2
, 10x10cm2
, 12x12cm2
, 14x14cm2
, 16x16cm2
and 18x18cm2
. The reading results of optic density
using X-RITE densitometer were converted to dose refering the characteristic curve graph of Gafchromic EBT2 that
had been prepared. Characteristic curve of the film have been made by giving 25cGy, 50cGy, 100cGy, 150cGy,
200cGy, 250cGy and 300cGy of dose to film strip in 2,5x3cm2
of field. The result of this research showed that in 5cm,
6cm, 7cm, 8cm and 9cm of the depth, can be obtained transmission factors 0.954, 0.952, 0.951, 0.950 and 0.948. A
great transmission factor change occured at the gantry angle position at 100o
to 120o
. Carbon fiber application for
the surface dose increased the relative dose from 10.9% into 37.4% (6x6cm2
), 16.9% into 48.39% (8x8cm2
), 23.0%
into 63.3% (10x10cm2
), 29.2% into 75.4% (12x12cm2
), 33.3% into 80.1% (14x14cm2
), 37% into 86.9% (16x16cm2
)
and 43.3% into 91.2% (18x18cm2
).
Keywords-- carbon fiber, surface dose, depth dose, cobalt-60
I. INTRODUCTION
In 2007, cancer was the second leading cause of death worldwide. Every year, more than 11 million new cases are
diagnosed, and more than seven million people die because of cancer, more than 70% of them are in developing
countries. If this current trends continue, new cases will increase to 16 million per year and more than 10 million people
will die because of cancer every year [1]. One of the technology developments on the cobalt-60 teletherapy machine is
the application of carbon fiber as the basic material of couch replacing racket. Carbon fiber is an ideal material of
examination couch in teletherapy, because its strong, rigid, lightweight and radiotranluscent. It also has a lower density
[2,3]. Carbon fiber density is (1.8 g/cm3
) lower than the density of steel (7.8 g/cm3
) or aluminum (2.8 g/cm3
) [2]. The
application of carbon fiber will result a low attenuation but give a significant increasing to radiation dose of skin, and
also affect the depth dose [3,4], it also significantly reduce the effects of skin sparing [5,6]. The application of carbon
fiber in the cobalt-60 machine will affect the maximum dose (Dmaks), where the depth of maximum dose will decrease
from 5 mm to 2 mm and surface dose will increase from 18% to 76% [4]. An irradiation in 10x10 cm2
of field showed
that surface dose increased four times greater than without carbon fiber [7]. Gantry angle also affects the amount of
attenuation and it is happened at 100o
-180o
of gantry position. Previous studies showed that the greatest attenuation was
happened at 120o
of gantry position with 6MV of photon energy exposure. The attenuation was 10% at 5x5 cm2
of field
and 8.3% at 10x10 cm2
of field [8]. The examination couch is variated into to models. They are racket model and solid
models that using a solid material like carbon fiber [6]. The racket model will result an attenuation between 0.06% to
0.39% depending on the energy and size of the field [9]. As the attenuation is very small, so the attenuation factor is
neglected in radiation planning [9].
II. METHOD
This study use cobalt-60 teletherapy machine type GWXJ80 from NPIC with 80 cm of SSD that utilizes carbon fiber as
the examination couch.

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Depth dose measurements have been performed using 0.65 cc ionization Extradin A12 detector with buildup cap wich
has been connected to the electrometer MAX4000 (Standard Imaging). Data was taken at (dref) 5 cm, 6 cm, 7 cm and 9
cm from carbon fiber couch with 10x10cm2
of irradiation field with and without carbon fiber at equal depth for each
gantry angle at 0o
- 360o
by 10o
of interval (Figure 1). Dose rate measurements procedure have refered to Technical
Report Series 398 (TRS 398) from IAEA. The attenuation is calculated by the equation:
atenuasi= × 100%..........................................(1)
where Do is a dose result without carbon fiber and D1 is a dose result with carbon fiber.
Figure 1. Measurement of the dose rate by using a buildup cap ionization detector; (a) dose rate measurement without
carbon fiber; (b) Measurement of dose rate after passing the carbon fiber; (c) A description of cros secsion
The surface dose was measured using Gafchromic EBT2 film. Gafchromic film characteristic curve was made before
data acquisiton. The procedure was irradiating the film (2.5x3 cm2
) which on the surface of the slab phantom (R320-
Virtual Water ™ Phantom) at the beam axis, with 25 cGy, 50 cGy , 100 cGy, 150 cGy, 200 cGy, 250 cGy and 300 cGy
of doses variation. Then, optical density of film was measured by a densitometer X-RITE then the optical density versus
the radiation dose (cGy) grap could be made. The results of the equation of the film characteristic curve was used to read
the surface dose. Surface dose was obtained by putting the Gafchromic film on the surface of the slab phantom, at the
beam axis then irradiated at various area 6x6 cm2
, 8x8 cm2
, 10x10 cm2
, 12x12 cm2
, 14x14 cm2
, 16x16 cm2
and 18x18
cm2
of field. Measurements were made with and without carbon fiber (Figure 2). The result of the optical density is
converted into dose value using the equation obtained before.
Figure 2. Measurement of surface dose by using Gafchromic film. (a) Surface dose with gantry 0o
without carbon fiber (b)
Dose surface with gantry 180o
with carbon fiber
III. RESULT AND DISCUSSION
Skin reactions due to ionizing radiation is occured in the epidermal tissue (+ 0.03 mm of thickness) and the dermis
(thickness + 13 mm). By radiation in megavolt order voltages, the maximum dose is occured in the basal layer where
skin sparing effects occur at this layer, so that the result of this radiation can hurt the skin causing fibrosis and
telangiectasia that may occur in the absence of the initial reaction [9]. Initial reactions such as erythema is occurred after
2-3 weeks followed by desquamation [8]. It needs to be understood that the dose amount at a few millimeters from the
surface of the tissue must really be a consideration in the planning of radiation, especially when a beam of radiation is
passing through the examination couch. The skin dose amount can be used for evaluation and investigation due to the
risk of radiation in radiotherapy [10].

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A. DEPTH DOSE
Figure 3 shows that carbon fiber affects the depth dose value, this change began in 100o
to 260o
of gantry position with a
different value. Very sharp decline occurred at 100o
-120o
and 240o
-260o
of gantry angle. Figure 4 shows that for 120o
of
angle transmission factor at 7 cm of depth seems increasing because not all of gamma rays pass through the carbon
fiber. A very high raising is hapenned in the gantry angle 110o
in which at 5 cm of depth, the transmission factor
increase directly. In this position, underdose or overdose of radiation exposure could be happened. On the gantry angle
130o
- 180o
, the decreasing transmission factor is relatively linear, because radiation beam wasn’t come out from carbon
fiber at 10x10 cm2
of radiation field. In Figure 4 also seen that the changes of transmission factor becoming smaller
when the gantry angle greater or less than 180°. It happens because the carbon fiber thickness which is passed by
radiation beam is greater due to the effect of inclination. There are changes of transmission value on the gantry angle
180o
and depth position at 5cm, 6cm, 7cm,8cm and 9 cm, respectively from 95.41%, 95.21%, 95.11%, 95.01% and
94.80%.
Figure 3: Graph transmission factor of various gantry angles and depths
Figure 4: Image transmission factor at gantry angle 180 ° with a depth varying gantry.
B. Surface dose
From Gafchromic EBT2 film irradiating at 2.5 x 3 cm2
with 25 cGy, 50 cGy, 100 cGy, 150 cGy, 200 cGy, 250 cGy and
300 cGy of dose, a third-degree polynomial regression equation between the optical density and radiation dose is
obtained:
5 cm 6 cm 7 cm 8 cm 9 cm
82%
84%
86%
88%
90%
92%
94%
96%
98%
100%
102%
5 6 7 8 9
TransmitionFactor
Depht (cm)180° 170° 160° 150° 140°
130° 120° 110° 100°

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y=2841.2 + 1461.4 + 788.16 .........................................(2)
In wich, value of the determinant is R2
= 0.9921.
Using equation 2 of surface dose, the results are obtained as shown as Tabel. 1. Table 1 shows that the application of
carbon fiber will increase the surface dose. At 6x6 cm2
of field, surface dose increase from 13.56 cGy into 46.62cGy (the
relative dose from 10.9% into 37.4%). While, the application of fiber carbon at 10x10 cm2
of field increase the surface
dose from 31.00 cGy into 84.84cGy (the relative dose from 23% into 63.0%). So, it can be concluded that the change of
field area and the application of carbon fiber will affect surface dose as shown at Table 1.
Figure 5: Graph curve Gafchromic EBT2 film characteristics Table 1: Dose surface without going through the carbon fiber and
through a carbon fiber with different irradiation field
IV.CONCLUSSION
From the research conducted, it conluded that the utilization of carbon fiber is not only having the advantage of being
strong and low density, but also increasing surface dose and affecting depth dose profile. So the use of carbon fiber
should be a concern when doing radiation planning, especially when the radiation beam passes through the carbon fiber.
Every teletherapy machine which utilize carbon fiber as couch examination material has different characteristic, so that
measurement of transmission factor has to do for each depth and the result of measurment is used to be a correction
factor in radiation planning.
REFERENCES
[1] Isabel Mortara, 2007. “The International Union Against Cancer”, US ONCOLOGICAL DISEASE.
[2] De Mooy LG, 1991. ”The use of carbon fiber in radiotherapy”, Radiotherapy and Oncology 22,pp:140-142
[3] Langmack,K.A. 2012. ”The use of an advanced composite material as an alternative to carbon fibre in
radioteraphy”, Radiography vol 18, pp.74-77.
[4] De Ost B, Vanregemorter L, Schaeken B and Van Den Weyngaert, 1977. ”The Effeck of Carbon Fibre insert on the
build-up and attenuation of high energy photon beams”, Radiotherapy and Oncology 45, pp.275-277
[5] Tulay P. Meydanci and Gonul Kemikler. 2008. ”Effect carbon fiber tabletop on the surface dose and attenuation
for high-energy photon beams”, Radiat Med 26, pp 539-544.
[6] Jan K.H. Seppala, Jarmo A.J. Kulmala. 2011. ” Increased beam attenuation and surface dose by different couch
inserts of treatment tables used in megavoltage radiotherapy”, Journal Of Applied Clinical Medical Physics,
Volume 12, Number 4, Pages 15-23
[7] Higgins D.M., Whitehurst P., Morgan A.M., 2001.” The Effect Of Carbon Fiber Couch Insert on Surface Dose with
Beam size Variation”, Medical Dosimetry, Vol. 26, No. 3, pp 251-254.
[8] Christopher F Njeh, Timothy W Raines and Mark W Saunders, 2009. ” Determination of the photon beam
attenuation by the BrainLAB imaging couch: angular and field size dependence”, Journal Of Applied Clinical
Medical Physics, Volume 10, Number 3, pp. 16-27
[9] John B. Simson, and Guy A. Godwin, 2011. ” The Effect Of The iBeamEvo Carbon Fiber Tabletop on Skin
Sparing”, Medical Dosimetry, Vol. 36, No. 3, pp. 330-333.
[10]. Brittany E.C., 2012,” The Effect of Treatment Couches on Delivered Dose During Radiotherapy Treatments”
Thesis, Master of Science in Radiological Health Physics San Diego State University, US.
y = 1461.x2 + 788.1x
R² = 0.992
0
50
100
150
200
250
300
350
- 0.05 0.10 0.15 0.20 0.25
dose(cGray)
Optical Density
FIELD SIZE
(cm
2
)
DOSE (cGy) RELATIVE DOSE/ (Dmax)
WITHOUT
CARBON
FIBER
WITH
CARBON
FIBER
WITHOUT
CARBON
FIBER
WITH
CARBON
FIBER
6x6 13.56 46.62 10.9% 37.4%
8X8 22.11 63.31 16.9% 48.3%
10X10 31.00 84.84 23.0% 63.0%
12X12 40.25 104.15 29.2% 75.4%
14X14 46.62 112.23 33.3% 80.1%
16X16 53.16 124.77 37.0% 86.9%
18X18 63.31 133.40 43.3% 91.2%