Institutional Repository | Satya Wacana Christian University: Analysis of Output Dose of The Photon Beam LINAC Using TRS 398 Protocol in R.S. Ken Saras
Analysis of Output Dose of The Photon Beam LINAC Using TRS 398 Protocol in R.S. Ken Saras Oleh : Wandi Wantoro NIM : 642012003 TUGAS AKHIR Diajukan kepada Program Studi Fisika, Fakultas Sains dan Matematika
guna memenuhi sebagian dari persyaratan untuk memperoleh gelar Sarjana Sains
Program Studi FisikaFAKULTAS SAINS DAN MATEMATIKA UNIVERSITAS KRISTEN SATYA WACANA SALATIGA 2017
ii iii
KATA PENGANTAR
Puji syukur kehadirat Tuhan Yang Maha Esa atas berkat dan karunia-Nya, penulis dapat menyelesaikan tugas akhir dengan judul “Analysis of Output Dose of The Photon Beam LINAC
Using TRS 398 Protocol in R.S. Ken
”. Penyusunan laporan penelitian ini berguna untuk memenuhi salah satu syarat tugas akhir dalam menyelesaikan studi fisika dan mendapatkan gelar Sarjana Sains di Universitas Kristen Satya Wacana.
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Tuhan Yang Esa yang telah memberikan ridho-Nya sehingga saya diberikan kelancaran dalam menyelesaikan tugas akhir ini dengan baik.
2. Kedua orang tua yang senantiasa mendukung baik secara moral, materiil, serta mendoakan dan membimbing saya.
3. Kakak yang senantiasa mendukung baik secara moral, materiil, serta mendoakan dan membimbing saya.
4. Dian Juniarti yang memberi motivasi dan dukungan.
5. Dosen-dosen yang memberi pengetahuan dan bimbingan selama perkuliahan.
6. Pembimbing lapangan yang memberi pengetahuan dan bimbingan selama pelaksanaan tugas akhir.
7. Teman-teman angkatan 2012.
Harapannya, laporan penelitian tugas akhir ini dapat bermanfaat di masa mendatang bagi pembaca. Penulis menyadari bahwa penyusunan tugas akhir ini memiliki banyak kekurangan. Sebab itu, penulis membutuhkan masukan berupa saran dan kritik yang bersifat membangun dari berbagai pihak ke arah yang lebih baik.
Salatiga, 8 September 2017 Penulis,
Wandi Wantoro iv
DAFTAR ISI
LEMBAR PENGESAHAN i
LEMBAR PERNYATAAN TIDAK PLAGIAT ii LEMBAR PERSETUJUAN AKSES iii
KATA PENGANTAR iv
DAFTAR ISI v
JURNAL
1 LAMPIRAN SERTIFIKAT SEMINAR SEBAGAI PEMAKALAH
11 v
Analysis of Output Dose of The Photon Beam LINAC Using
TRS 398 Protocol in R.S. Ken Saras 1 1* 1 Wandi Wantoro , Giner Maslebu , Suryasatriya Trihandaru and Muhamad 2 1 Hidayatullah 2 Physic Department of Universitas Kristen Satya Wacana, Salatiga, IndonesiaRadiotherapy Unit of Rumah Sakit Ken Saras, Ungaran, Indonesia Abstract. Analysis of output dose of the photon beam LINAC in Radiotherapy unit of R.S.
Ken Saras using TRS 398 protocol has done. This analysis was done to determine whether the output dose from photon beam LINAC in Radiotherapy unit of R.S. Ken Saras has an output dose deviation smaller than 2% or not. The measurement using Scdx-Wellhöfer FC65-G/IC70 ionization chamber in the solid water phantom with 100 cm SSD and 10 cm × 10 cm field size. From the calculation, it was found that the average output dose of the photon beam at the reference depth dose (DW,Q(zref)) was 0.668 cGy/MU and the average output dose of the photon beam at maximum depth dose (DW,Q(zmax)) was 1.003 cGy/MU. The output dose has 0.7% output dose deviation so it is concluded that the LINAC at Radiotherapy unit of R.S. Ken Saras is still properly for radiotherapy activities.
Keywords: Output Dose, TRS 398, Output Dose Deviation.
- Corresponding author: ginmaslebu@gmail.com
1
1. Introduction
Radiotherapy is a therapy method by using ionizing radiation that is effective to treat cancer [1] patients. In radiotherapy, there are many instruments that one of them is Linear Accelerator [2] (LINAC). Today there are many hospitals which use LINAC as their radiotherapy instrument.
LINAC is a radiotherapy instrument which can produce an output of photon beam in MV energy [3] and electron beam in MeV energy.
LINAC can produce photon beam by hitting accelerated electrons into heavy metal to [4] generated x-rays were used for cancer treatment in radiotherapy. Photon beam will have interacted with the cells of the body result of ionization and excitation on the atomic composer of the cell then followed by the change of molecular structure of the cell so that the cell damage [5] occurs. Like the other radiotherapy instruments, output dose of LINAC also has output instability [6] because LINAC was made by interconnected electronic circuits. This output instability occurs in the output dose of the electron beam and photon beam. To overcome such instability, Quality [7] Control (QC) measures are needed.
Quality Control is the regulatory process through which the actual quality performance is measured, compared with existing standards, and the actions necessary to keep or regain [8] conformance with the standards. Based on the frequency of QC implementation time, QC is divided into daily QC, weekly QC, monthly QC and annual QC. There are various procedure or item to be tested in the QC implementation of LINAC, one of them is the photon beam output [9] constancy. To maintain the photon beam output constancy, analysis of output dose from photon beam LINAC is necessary to determine whether the output dose of the photon beam is required of [10] calibration or still appropriate with the standards. In the execution of analysis output dose of the photon beam is known by the protocol to determining output dose Technical Report Series no. 398 (TRS 398).
TRS 398 is an international protocol which made by the International Atomic Energy Agency (IAEA) as a code of practice for determining the absorbed dose of an external radiation [11] based on water absorbed dose. TRS 398 is made to reduced the uncertainty by fixing an earlier [12]
TRS based on the primary standard of air kerma for determining the absorbed dose. Based on the problems already described, it is important to analyze the output dose of the photon beam LINAC using TRS 398 protocol.
2. Methods
2.1 Measurement The Output Dose of The Photon Beam The measurement of output dose of the photon beam was performed on a Siemens Primus
LINAC that used in the radiotherapy unit at Ken Saras Hospital. The measurement of output dose of the photon beam is done every 07.00 WIB except for the holidays on 2 January 2017 until 25 March 2017 according to daily QC procedure while Percentage Depth Dose (PDD) measurement is done once in a month according to monthly QC procedure. The measurements were made with 100 cm Source to Skin Distance (SSD) and 10 cm × 10 cm field size area in the solid water phantom using Scdx-Wellhöfer FC65-G/IC70 Farmer detector as shown in Fig 1. The irradiation was done 3 ref times at 300 Volt, - 300 Volt and 100 Volt with a depth of z .
FIGURE 1. Set Up of The Output Dose Measurement
2 The z ref or depth of the reference dose (in g/cm ) is obtained from TRS 398 and depends on 2 2 the value of Tissue Phantom Ratio (TPR 20,10 ). The value of z ref is 10 g/cm or 5 g/cm (for Co-60 2 photon beam) if the value of TPR 20,10 is smaller than 0.7 and The value of z ref is 10 g/cm if thevalue of TPR 20,10 is greater than or equal to 0.7. TPR 20,10 is the ratio of Percentage Depth Dose 2 2 (PDD) at depth of 20 g/cm and 10 g/cm in water phantom which measured at 100 cm SSD and 10 [11] cm × 10 cm field size area or can be written as,
PDD
20 TPR 0,0595 (1) =1,2661
- - 20,10
PDD
10
2.2 Analysis of Output Dose of The Photon Beam To calculate the absorbed dose, it is necessary to know the value of factor correction such as k TP , k elec , k s , k pol , k Q,Qo and N D,W,Qo . k TP is a factor to correct of the response of an ionization
3 chamber for the effect of difference temperature and air pressure on the radiotherapy unit to the [11] standard reference conditions, define as,
273,15 + T P
(2)
k = TP 273,15 + T P
Where T is the temperature and P is the air pressure at the measurement of the photon beam, o T and P are the standard reference conditions at 20 C and 101.3 kPa air pressure. k elec is an electrometer calibration factor whose the value is obtained from the calibration certificate of the electrometer. k s is the correction factor of the ionization chamber response to the incomplete [11] collection of charge due to ion recombination, which can be written as,
2 M M
1
1
(3)
k = a + a s
1 ( ) + a
2 ( ) M M
2
2 Where the value of a is 1.198, a 1 is -0.8753, a 2 is 0.677, M 1 is measured values of collecting charges at the polarizing voltages 300 Volt and M 2 is measured values of collecting charges at the polarizing voltages 100 Volt. k pol is a factor to correct the response of an ionization chamber for the
effect of a change in polarity of the polarizing voltage applied to the chamber, which can be written [11] as,
|M | + |M |
−- pol
(4)
k =
2M
- + Where M is the dosimeter readings at the polarizing voltage 300 Volt and M˗ is a dosimeter reading at the polarizing voltage - 300 Volt. k Q,Qo is a correction factor of the difference between the response of the ionization chamber in the quality of the used photon beam as the chamber calibration in the reference beam quality. The value of k Q,Qo are obtained from TRS 398 which depend on the type of used chamber and the value of the TPR 20,10 . N D,W,Qo is calibration factor in terms of absorbed dose to water for a dosimeter at a reference beam quality and the value of N D,W,Qo is 0.047 Gy/nC. [11]
- – 9719 [3] Sung-woo Kim et al. 2015. Measurement of Electron Beam Output for the Prototype Compact Linac.
- – 3128 [6] Khifiyah, Mariatul et al. 2014. Analisa Kurva Percentage Depth Dose (PDD) dan Profile Dose Untuk Lapangan Radiasi Simetri dan Asimetri Pada Linear Accelerator (LINAC) 6 dan 10 MV. Youngster Physics Journal. ISSN : 2302 – 7371.
The output dose of the photon beam at reference depth dose (z ref ) can be expressed, (5)
D (z ) = M . N . k
W,Q ref Q D,W,Q Q,Q
Where M Q is the reading of the dosimeter with the reference conditions and corrected with [11] the correction factors or can be written as, (6)
M = M Q 1 . k TP . . k pol . k s
The output dose of the photon beam at reference depth dose D (z ) is then used to
W,Q ref
calculate the output dose of the photon beam at maximum depth dose D (z [11]
W,Q max ) which can be
expressed as, (7)
D (z ) = 100 D (z ) / PDD(z )
W,Q max W,Q ref ref4 The deviation of the output dose of the photon beam can be expressed,
(z ) - D |D W,Q max W,Q std|
(8) % deviation = ×100%
D std
W,Q
Where D std (in cGy/MU) is the value set for the output dose of photon beam per monitor
W,Q units (MU) in LINAC.
D std of the LINAC in radiotherapy unit of R.S. Ken Saras is set to 1
W,Q cGy/MU.
3. Results
3.1 PDD Measurement The measurement of the PDD of the photon beam use an ionization chamber in a water phantom with 100 cm SSD and the results are shown in Fig 2. From the measurement it is found that the maximum depth dose (z max ) is at the depth of 1.5 cm
100
90
80
70 )
60 (%
50 DD P
40
30
20
10 1,5
3
6
9
12
15
18
21
24
27
30 Depth (cm)
FIGURE 2. PDD of The Photon Beam
( ) on January, ( ) on February and ( ) on March.
3.2 Analysis of The Correction Factors Measurement of the output dose of the photon beam is taken out at an average ambient temperature and air pressure on January of 19.74° C and 95.3 kPa, on February of 21.3° C and 95.6 kPa, and on March of 20.8° C and 95.5 kPa. That values are then used to calculate the correction factor k TP using Eq. 2 whose the value is seen in Table 1. The average dosimeter reading charge of the photon beam at operating voltages 300 V, -300 V and 100 V on January is 26.18 nC, 26.74 nC and 26.09 nC, on February is 26.26 nC, 26.30 nC and 26.17 nC, and on March is 26.30 nC, 26.80 nC and 26.21 nC with every measurement are performed in setting of MU (Monitoring Unit) is
5
200. From the dosimeter reading charge is calculated the value of k pol using Eq. 3 and the value of k s using Eq. 4 which each value can be seen in Table 1. The value of calibration factor of electrometer which written in certificate of Calibration performed by National Nuclear Energy Agency of Indonesia (BATAN) is 1.
TABLE 1. The Value of Correction Factors Corection Factor Month
N D,W,Qo
k TP k s k elec k pol k Q,Qo
(Gy/nC) January 1.059 1.001 1.000 1.010 0.997 0.047
February 1.064 1.001 1.000 1.000 0.997 0.047 March 1.063 1.001 1.000 0.990 0.997 0.047
Average 1.062 1.001 1.000 1.000 0.997 0.047
4. Discussion
4.1 PDD Analysis The PDD of the photon beam is increase from the depth of 0 cm to the maximum depth dose at 1.5 cm which then called as the build up region because when photon beam have interacted with the phantom it takes a certain thickness of tissue to reach the maximum dose or called the skin [8] sparing effect. After reach the maximum depth dose, the PDD of the photon beam will decrease to 0 which is called the attenuation region. From the data in Fig. 2 it is found the value of PDD at 20,10 10 cm is 66.4% and at 20 cm is 37.81% which is used to calculate the value of TPR with Eq. 1, 20,10 20,10 the calculated value of TPR is 0.66. Due to the value of TPR is smaller than 0.7 and the ref 20,10 2 photon beam analyzed is not sourced from Co-60 then the z is 10 g/cm . The value of TPR is Q,Qo also used to determine the value of correction factor k which can be seen in Table 1.
4.2 Analysis of Output Dose of The Photon Beam The value of correction factor k TP , k elec , k pol , and k s is used to calculate the M Q using Eq. 6 so obtained that the value of M Q which can be seen in Fig. 3. It is obtained that the average value of
M Q is 0.139 nC/MU. The values of M Q , k Q,Qo , and N D,W,Qo are used to calculate D W,Q (z ref ) using Eq. 5 which the value is then used to calculate D W,Q (z max ) using equation 7 which can be seen in Fig. 4.
6
7 FIGURE 3. The Value of M Q
5 7 9 11 13 15 17 19 21 23 D W ,Q (z ref )
0.2
0.4
0.6
0.8
1
1.2
1
3
(cGy /MU) Days
5 7 9 11 13 15 17 19 21 23 D W ,Q (z ref )
0.2
0.4
0.6
0.8
1
1.2
1
3
5 7 9 11 13 15 17 19 21 23 D W ,Q (z ref )
(cGy /MU) Days
3
( ) on January, ( ) on February, ( ) on March and ( ) the average value of M Q
0.16
From Fig. 4a is found that the average value of D W,Q (z ref ) is 0.671 cGy/MU and the average value of D W,Q (z max ) is 1.007 cGy/MU. From Fig. 4b is found that the average value of D W,Q (z ref ) is 0.669 cGy/MU and the average value of D W,Q (z max ) is 1.005 cGy/MU. From Fig. 4c is found that the average value of D W,Q (z ref ) is 0.663 cGy/MU and the average value of D W,Q (z max ) is 0.996 cGy/MU. From the measurement at January until March obtained that the average value of D W,Q (z ref ) is 0.668 cGy/MU and the average value of D W,Q (z max ) is 1.003 cGy/MU.
(a) (b)
(c)
FIGURE 4. The Value of D W,Q (z ref ) and D W,Q (z max )
(a) on January, (b) on February, (c) on March, ( ) D W,Q (z max ) and ( ) D W,Q (z ref )
0.12
0.13
0.14
0.15
1
1
3
5 7 9 11 13 15 17 19 21 23 M Q (n C /MU)
Days
0.2
0.4
0.6
0.8
1
1.2
(cGy /MU) Days Using the Eq 8, obtained that the output dose deviation of the photon beam LINAC at the radiotherapy unit of R.S. Ken Saras which can be seen in Fig. 5. It is found that the average output dose deviation of the photon beam on 2 January 2017 to 25 March 2017 is 0.7%. Based on the
IAEA recommendations on his book entitled Accuracy Requirements And Uncertainties In Radiotherapy which published in 2016 that the output dose deviation of photon beam for clinical [13] purposes should be smaller than 2% then the photon beam of the LINAC at the radiotherapy unit of R.S. Ken Saras are still properly for radiotherapy activities.
2
1.6 %)
1.2 ( n
0.8 iatio
0.4 Dev
1
3
5 7 9 11 13 15 17 19 21 23 Days
FIGURE 5. Output Dose Deviation of The Photon Beam
( ) on January, ( ) on February, ( ) on March and ( ) tolerance limit
5. Conclusions
From the measurements on 2 January 2017 to 25 March 2017, it is found that the LINAC at Radiotherapy unit of R.S. Ken Saras has the average output dose of the photon beam at the reference depth dose (D W,Q (z ref )) is 0.667 cGy/MU and the average output dose of the photon beam at the maximum depth dose (D W,Q (z max )) is 1.002 cGy/MU. The photon beam of LINAC at Radiotherapy Unit of R.S. Ken Saras has the average output dose deviation is 0.7% which is still smaller than the tolerance limit set by the IAEA that is 2% so it is concluded that the LINAC at Radiotherapy unit of R.S. Ken Saras still properly for radiotherapy activities.
6. References
[1] Nordström, Fredrik. 2012. Quality Assurance in Radiotherapy : Development and evaluation of new tools for improved patient safety in external beam therapy. Media-Tryck. Lund University. Lund. [2] Sahoo, S.K..2012. Commissioning of a Modern LINAC for Clinical Treatment and Material
Research . International Journal of Trends in Interdisciplinary Studies. ISSN: 0976
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[4] Anam, Choirul. 2011. Kajian Spektrum Sinar-X 6 MV Menggunakan Simulasi Monte Carlo.
Universitas Diponegoro Semarang. ISSN: 1410 – 9662. [5] Suharni et al. 2010. Tinjauan Teknologi Akselerator Linear (LINAC) Elekta Precise di RSUP
Dr. Sardjito . Prosiding Pertemuan dan Presentasi Ilmiah Teknologi Akselerator dan
Aplikasinya. ISSN 0216
[7] Hossain, Murshed. 2015. Output Trends, Characteristics, And Measurements Of Three Mega- Voltage Radiotherapy Linear Accelerators. J Appl Clin Med Phys. ; 15(4): 4783
[8] IAEA. 2005. Radiation Oncology Physics: A Handbook For Teachers And Students. IAEA, Vienna,
[9] Bissonnette, Jean-Pierre et al. 2012. Quality assurance for image-guided radiation therapy utilizing CT-based technologies: A report of the AAPM TG-179. AAPM. pp 0094-2405. [10] Suharni et al. 2013. Analisis Hasil Pengukuran Percentage Depth Dose (PDD) Berkas
. Prosiding Pertemuan dan Presentasi Ilmiah
Elektron LINAC Elekta RSUP Dr. Sardjito Teknologi Akselerator dan Aplikasinya. ISSN 1411-1349.
[11] IAEA. 2000. Technical Report Series no.398: Absorbed Dose Determination in External Beam Radiotherapy. IAEA, Vienna. [12] Sang Koo Kang et al. 2014. Determination of TRS-398 Quality Factors for Cs-137 Gamma Rays in Reference Dosimetry . PROGRESS in MEDICAL PHYSICS.
10.14316/pmp.2014.25.3.123. [13] IAEA. 2016. Accuracy Requirements And Uncertainties In Radiotherapy. IAEA, Vienna.
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