2chnolog>', Vol 5. N'o 4 (201:
Application of Monte-Carlo Code to dose distribution calculation in a case of lung cancer by the emitted photon beams
from Linear Accelerator
Le Thanh Xuan', Nguyen Thi Cam T h u " , Tran Van Nghia', Vo Thanh Nhon'. Tniong Thi Hong Loan=
'Institute for Computational Science and Technologi al Ha Clu Mini, Clp
•Unnertily OfScience. 227 Nguyen Van CuSoeet Ward A. Di.anct 5 Ho Cia Mmh Citv General Hospital of Kien Giang ~45LeLoi Street Rach Gia Cm. Kien Giaiig '
Email ntcthu@hcmu^ edu vn (ReceivedOl October 2015. accepled 31 December 2015)
Abstract: The dose dislribulion calculanon is one of the major steps m radiotherapy In this paper the Monte Carlo code MCNP5 has been applied for simulalion 15MV photon beams emmed from linear accelerator in a case of lung cancer of the General Hospital of Kien Giang The settings for beam directions, field sizes and isocenler posinon used in MCNPS must be the same as those in treatment plan at the hospital to ensure the results from MCNP5 are accurate We also built a program CODIM by usmg MATLAB programmmg solnvare This program uas used to construct patient model from ung CT images obtained ffom cancer treatment eases at the General Hospital of Kien Giang and then MCNPS code was used to simulate the delivered dose in tbe patient The results hom MCNPS show thai there is a difference of S% m comparison with Prowess Panlher program - a semi-empirieal simulation program which is bemg used for tteatment planning in the General Hospital of Kten Giang The success ot the work will help the planners to verify the patient dose dismbution calculated from tbe treatment planning program being used at the hospital
Keywords: liuuc. radiotlieiapy ahsorheddo^e. timgiuncei. \ICNP5
I. INTRODUCTION difficult and complicated One of the most The lung cancer causes the highest death ™ " ' " " " ' " " ' ™ " ' " ' " ' ' ° * '°' '""S! '^™«'- '"^
rate .among other cancers It is 13% in all ' " "'""•'=' "' '"""lo'h^i-apy. In fact, cancer, but cancer death rate is 2 8 % over the ™ " ' ° ' ' ' ""= "'= P*"""" '""'"' ''"" "
world [ I ] . In Vie, Nam, iung cancer rate is ° " " " " ' '""" " " '""" "'^^'''^"t'" "> I"" the abou, 29.6/100000 for men (the second-most " " " " " ' ' ' ° ' ""'"'"'"' " " " ' " " ' " ""==""'="' commonly diagnosed cancer after hver cancer " ' " ' ' ° * ' " ' " ' "' " P " " ' ™ ' "chemotherapy fot men), lung cancer is also one of the founh "' "^ " ' ' - ' " " " « - " " x ™ ™ * » " ' depth mos, common cancer with rate of 7 7/100000 ° ' *"'" '-•™'™"='"s ""<'<" ^kin surface and for women [2] The major risk factors for lung ' " " " " ° * " " « ' ' " " " " * ''°'^^- "'= P^Mon beam cancer are cigarette smokins lomzing " " ' °"'^ ' ' " ' " " ' ' ' ' " " " " " S ^ « ' ™ "
ladiation. and vims. Lons-tem, Exposure of ' ' " ' ' ' ' ° ' " ' " ' " = ' ' ' ' " = ' " " " ^ Y "
Ihese factors causes changes ,n D N ^ of ' ' ' " ' ° " '''"''''°"' " ' ™ ' ' ' " « ^his facor is the bronchus (bronchus epithelium) If there are '="'''"8 =»""= "fiiislnbuttng high radiation dose many injured tissues, the lung cancer °-" " ° " " ' ' ' " " " ' " ° ™ ' ' • " " ' ° ' ' ' "" ""= "'^"SY.
probabilil> seems increasingly The"detection *"^''' ^"'' '""'' ^ ' ° ' ' ' '^''"P' "" '•"/"n'Eclly and treatment for lung cancer is extremely ''•'''"'='"^<'- '^e tumor will not receive enough
radiation dose and Ihe nomial tissue will absorb
lociciv and \"icinani -Xiomic f ner<'\ Institute
Of MO\TE-CARLO CODE TO DOSE D1STR1BITI0\L \LCLL ATION ->:-ui!. the treatment for patient
IS not .f-,i\ effectne but also causes the une\pec!ed results. Nowadays, the semi- empincal radiation dose calculation programs in hospitals can calculate fast, but it is limited in accuracy [3] and the Monte Carlo method is so-called the gold standard of other methods[4, 5] with \ei-y high accuracy Therefore, in this work, we use the Monte Carlo method in MCNTS [6] to simulate the electron beam that
emitted from the window of linear accelerator and hits the target to create 15MV photon beam for treatment planning in a lung cancer case at the General Hospital of Kien Giang III other to accurately calculate the radiation dose distribution when the photon beam go mto patient body.
II. MATERIAL A \ D METHOD In this work, we use Monte Carlo code MCNP5 to simulate the Primus Imear accelerator (SIEMENS) in the General Hospital of Kien Giang for dose distnbution calculation in patient body that is radiated by its photon beam- The patient model is created by importing CT images of the lung cancer case into the treatment planning system of the General Hospital of Kien Glang We also use Matlab code (CODiM) [7] for"creating mpul used in MCNPS. processmg output, and image
\iewing
The Head Configuration of linear accelerator PRIMUS HPD with 15MV photon beam
The head configuration that is created m MCNP5 IS based on receiving necessary parameters such as dimensions and physical properties of important components of the head After completing importing data. Visual Editor program of MCNP5 will process and export a 2D nnage of head configuration (see Figure I) 111 order to receive high qualit>- electron beam
and accurate results, the simulation is executed after the electron beam exits from the window of accelerating system
Window
- . - ^ ^ ( t ™
• Micji plale Fig. 1. 2D image of head configuration in linear accelerator is created by Visual Editor in MCNP5 for I5MV photon beam [7]
The source of 15Kfl^photon beam The simulated source in MCNP5 that creates the 15MV photon beam is the electron source m disk shape with a radius of l,5mni and within the energy spectrum from 0.7MeV to 15 5MeV with emittmg probability given in the Table I
Table I. Energy bands and emitting probability of the electron beam to create I5MV photon beam [7],
Energy band(MeV) 0 . 7 - 9 0 9 , 0 - IOO 1 0 0 - II 0 I 1 . 0 - I I . 5 11 5 - 1 2 , 0 1 2 0 - 12.'^
1 2 . 5 - 13 0 13 0 - 1 3 . 5 1 1 3 5 - 1 4 0 1 4 . 0 - 1 4 5 14 5 - 1 5 . 0 i' 1 5 0 - 1 5 5
Probability 7 6 0 x I0-"
1 3 8 x 1 0 "
4,29 X 10^
7 3 6 x 1 0 ' 4,52 X 10'' 4,52 X I0-' 4,74 X 10"' 4,29 X 10^
2 8 7 x 1 0 ' 1,31 X 1 0 "
3 9 3 x 1 0 ' "
7 6 2 T | ( F '
'
JN THI CAM THL ei al C T images
The CT images for simulation are obtamed from a lung cancer case at the General Hospital of Kien Giang that are captiu-ed by the CT simulator (SIEMENS), The image has 512x512 pixel resolution The size o f a pixel is about 0.8945x0,8945 mm^ and slice thickness is 6mm (Figure 2) These parameters are received from CT image header infonnation.
r- 0.894SmB 0.8945 BB-*^ I
pixel r- 0.89
VCWBI
Fis- 2. The voxel size of CT image [7]
Patient Model
The patient model is designed for MCNP5 input data by using CODIM program {see Figure
3). Each CT number on the CT image is convened into a densitv' and a conesponding material element in the patient model Each voxel size in patient model equals each voxel size of each CT slice (these parameters are receiv ed from CT image header infonnation).
Setting photon btams for simulation of CT images Simulation is earned out with three 15IVIV photon beams, Isocenler posinon' X =0,8cm, Y
=2 5cra. and Z —90.3cm as following - The first beami at 60° from the venical line with superior-inferior direction, field size is I 3cm X 10.8cm (the dimension on x and y axis, respectn el)), selected beam quality is 100%
The second beam, at 154" from the vertical line with infenor-supenor direction.
field size IS 10 3cm x 10.8cm (the dimension on and V axis, respectively), selected beam qualit> IS 100%
fhe third beam- ai 330' from the vertical Ime with infenor-supenor direction, field size is 10 4cm x 10 6cm {the dimension on
and y axis, respectively), selected beam quality is 100°o
APPLICATION- OF MONTE-C.\RLO CODE TO DOSE DISTRIBUTION CALCULATION'
Fig.4. The CODIM program (Isodose^Meshtal) shows patient dose distribution with three photon beams o the center CT image in MCNP5
III. RESULTS AND DISCUSSION CalculaHng patient dose distribution in MCNPS program and comparing with the Prowess Panther program.
After completing the calculation MCNPS. CODIM program analyzes outpu! data and displays patient dose distribution on each CT image The achieved images of the distribution of ditTerent relative dose values are displayed in Figure 4
Figure 5 shows patieni dose distnbution in MCNPS and Prowess Panther program. The high dose region of the tumor and the low dose regions that are far from the tumor are represented in different colors In Figure 5A, in order to distinguish the radiation dose regions easily, it has named as the following; dark red, brighl red. red. and orange fn the dark red region, the highesi patient dose distribution on tumor corresponds to the lOO^'c, isodose line and marked NMIH pomt O. the bright red region is
marked with point A corresponding to the 95%
isodose line, the red region is marked with point B corresponding to the 90% isodose line, and the orange region is marked with point C corresponding to the 85% isodose line. Figure 5 also show.s that the isodose distnbution that are calculated by MCNPS and Prowess Panther program has a fairly good matching The good matching is at the high dose regions, ll is possible to discnminale different dose regions by the difference in the colors. Max isodose in MCNPS IS at the center of the tumor and the same as Prowess Panther program,
Addiiionally. Figure 5A shows that MCNPS calculates the patieni dose distribution when the photon beams go through the fixed mask used in beam directions 60" and 330" anti the treatment couch m beam direction 154".
Meanwhile, in Prowess Panther planners had rejected above factors in the oalculaling patient dose distribution (^ee Figure SB)
EN THI CAM THU et;
f-^' (B) Fig.5. (A) Isodose distnbution in MCNPS and Prowess Panther (B
Table II Coordin e and relative dose calculated by MCNPS Position
'
Pixel coordinates
(297,251) (275,261) (264.269) (251.278)
Relative dose in MCNPS
(%)
100 93 6 92 5 90 1
Relative dose in Prowess Panther (%)
IOO 95 0 92 0 88.0 Table II shows calculated relative doses
in MCNP5 and Prowess Panther program at four points that are marked in Figure 5A In this table, the relative dose ratios in MCNP5 and Prowess Panther piogram are the same at different dose regions When using relative doses, the MCNP5 also clearly distinguish the different relative dose regions 98%, 95%, 92%.
and 88% and the sante as the Prowess Panther program The difference between the reference points IS lower 5%,, It is enough small to accept the agreement of the results between MCNP5 and Prowess Pamher This difference between two programs can be explained as following The quite high nuctuation of results in MCNP5 program are caused by the not enough long calculating tune [8] As a result, radiation dose region separation is not clear The radkation dose regions have still many overlapping points, w hich causing the interference in dose
Meanwhile, the Prowess Panther program used semi-empincal data and deterministic algorithm, so relative dose calculating based on fixing expenmental data and approximation methods leads enors In addition, in the calculation process, the planners automatically removes some objects on the CT images such as fixed masks, lead markers, and treatment couch, which causes enors Another reason that also be mentioned here is the limitation of CODIM program in using the kerma data set convened into the absorbed dose data set of tissues, while the convened factor used m the Prowess Panlher program has the different value On the other hand, parameters such as intcnsitx-. radiation time, field sizes, and exact composition of the components of the linear accelerator head can also cause the diffeience between two programs
APPLICATION OF MONTE-C.ARLO CODE IV. C O N C L U S I O N Through studying the head configuration of PRIMUS linear accelerator used m radiation therapy and based on the data set of the limg cancer case at the General Hospital of Kien Giang, we have applied the MCNPS program to simulate the patient dose distribution. The error of achieved results is lower 5% when comparing with the commercial Prowess Panther program bemg used at the hospital The more accurate radiation dose calculation by Monte Cario code w ill help the medical physicists to venfy the patient dose distt-ibution calculated from the freatment planning program being used at the hospital
ACKNOWLEDGMENTS We thank Dang Nguyen Phuong (University of Freiburg) for helpful discussion Compuling resources provided by the Institute for Computational Science and Technology - Ho Chl Mmh City are gratefully acknowledged.
This research was also funded by Incubation Program of Creative Science and Technology for Youth - Center ofScience and Technology Development for Youth. The authors would also like to thank the General Hospital of Kien Giang for providing the patient data which is calculated on Prowess Panther program
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