MO PHONG PHU'ONG PHAP XA TRI DIEU BIEN ClTdNG D Q BANG VIEC Sir DVNG PENELOPE
TRAN QU6C THAI, LY ANH TU
Khoa Khoa hgc img dung, Tnrdng Dai hgc Bach khoa thdnh phd Ho Chi Minh 268 Ly Thudng Kiet, Q.IO, TPHdChiMmh
Email: tqihai2810@gmaiLcom
Abstract: In this paper we present about the simulation of intensity modulate radiation therapy (IMRT) with PENELOPE. The simulation of IMRT in here involves two problems, the first is the modulation with tomotherapy and the second is the modulation with the movement of the multileaf colimator. Obtained results is the distribution of absorbed dose on the target volume and the organs at risk (OARs). The resuhs show that IMRT could give a desired distribution of dose, which is enough for the target to kill the cancer cells and prevent the over dose to OARs. This paper also shows how to use PENELOPE for studies of the distribution of absorbed dose in radiotherapy.
Tir khda: Xg tri, mo phdng bdng PENELOPE, IMRT.
I. GI61 THIEU
Ngay nay, ky thuat xa tri la mot trong nhimg l\ra chon hang dau trong cac Heu phap dieu tri ung thu. Ciing voi su phat trien ciia cac k^* thuat chuan doan hinh anh thi phuong phap xa tri hien dai da dat duoc su phat trien to Ion trong viec tieu diet cac te bao ung thu voi do chinh xac cao va an toan doi vol benh nhan. Ky thu^t xa tri dieu bien cuong do IMRT la mgt minh chung cho dieu nay. Do vay viec khao sat phuong phap IMRT dac biet la su phan bo lieu hap thu trong IMRT la van de dugc quan tam rat Ion ca trong nghien cuu va umg dung.
PENELOPE-cbuong trinh may tinh su dung ngon ngii FORTRAN 77 thuc hien mo phong Monte Carlo su van chuyen cua electron, photon va positron trong m6t vat li?u bat ky voi m6t khoang nang lugng rpng, tu vai tram eV den khoang 1 GeV [1]. Bdo cao nay trinh bay ve su tinh toan phan bo Heu doi voi cac bai toan chieu xa phiic tap nhu IMRT bSng PENELOPE.
II. THUC HIEN MO PHONG
Su mo phong trong bao cao nay dugc chia thanh 2 bai toan: 1.M6 phong su diSu biSn cucmg do chi8u xa thong qua su thay d6i vi tri cua cac la trong he bp chuin true da la (MLC) va 2. Mo phong su di^u bien cuong dp thong qua phep chiSu xa cit 16p (tomotheraphy).
Hinh 1: Khdng gian mdphdng bdi todn I
D6i vai bai toan mo phong 1, khong gian mo phong la he mini MLC ttmgsten kich thuoc 10 mm x 30 mm x 60 mm bao g6m 20 cap la dich chuyin dpc lap, va phantom mo mhm kich thuoc 10 mm x 8 mm x 2 mm dat vuong g6c voi trucmg chieu dugc chia thanh 80 voxel.
Kich thuoc nay dugc lay tir kich thuoc that cua h^ miniMLC dCing trong xa tri viing dciu, nao [2].
Hdi nghi Khoa hgc vd Cdng nghi hgt nhdn todn qudc idn thu IX, Ninh Thudn 18-19/8/2011 561
Phep dihu bihn a day dugc chia lam 5 phan doan ung vcri 5 dinh dang cua he MLC.
Chiim photon dugc lira chon mo phong co dac tinh giong nhu chiun phonton o ddu ra ciia tbiht bi xa tri Co-60 do la:
Nang lugng 1.25 MeV.
- Chum song song phu kin h^t truong chilu cua MLC (chSng ban truong chieu o day la 10mm x 10 mm doi vdi he miniMLC).
Lira chpn chum tia song song trai deu trong mat phang 10 mm x 10 mm la vin dh quan trong dh dam bao su chinh xac ciia phep mo phong. Cf bai mo phong nay chung toi mo phong nguon song song bang mpt he thong nguon don rai deu trong mat phing chieu xa 10 mm x 10 mm each he mini MLC 10 cm.
Hinh 2: Ludi phdn bd cdc vi tri ngudn chieu xg bdi todn 1 Doi voi bai toan mo phong thu hai, khong gian mo phong van la he MLC nhung co sir dich chuyen vi tri cua he MLC xung quanh mo dich de tao su phan lieu toi uu. Bai mo phong nay tien hanh tinh toan voi 16 truong chieu co ban xung quanh khoi u dang chii C (la dang khoi u pho bien trong dieu tri vung dau - c6 va cdn ap dung IMRT)
Hinh 3: Khong gian mdphdng bdi todn 2 III. KET QUA vA THAO LUAN
Doi voi bai toan I, tir file DAT cho ket qua nang lugng hap thu tai cac khoi da dugc djnh nghTa, do la nang lugng tren 80 voxel phantom cua 20 cap MLC - cac gia tri dugc quan tam. Cac gia tri nay dugc chuyen sang dang ma tran dh xir ly va hien tbi ket qua ciia 5 phan doan chieu.
562 Hdi nghi Khog hgc vd Cdng nghe hgi nhdn loan quic lin thiIX, Ninh Thugn 18-19/8/2011
total .1.0et004 '[O.OKM 0.02SS 0.0717 0.2510 0.2540 0.0662 0.0Z75 0.0094
0.0277 0.0841 0.29S4 0.5142 0.5193 0.2981 0.08i9 O.OZ76
0.0754 0.3026 0.5562 0.7885 0.7879 0.5574 0.3050 0.0755
0.2823 0.5587 0.8208 1.0548 1.0500 0.8172 0.5537 0.2835
0.4803 0.7762 1.0469 1.2698 1.2754 1.0402 0.7733 0.4734
0.4835 0.7804 1.040!
1.2631 1.2789 1.0S64 0.7791 0.4804
0.2824 0.5547 0.8165 1.0424 1.0410 0.8180 0.5541 0.2803
0.0761 0.2998 0.5536 0.7714 0.7762 0.5582 0.3017 0.0745
0.0273 0.0818 0.2965 0.5028 0.5062 0.2956 0.0803 0.0266
0.0095;...
0.0273;...
0.0692;...
0.2504;...
0.2521;...
0.0703;,..
0.0267;...
0.0091]
-a
Hinh 4: Kit qud diiu biin cudng dg cua bdi todn 1
Qua bai mo phong s6 1 nay cho thay phep xa tri dieu bien cuong dp IMRT cho phep co thi thay d6i nang lugng hip thu tren v$t chdt trong mot khoang gia tri nang lugng tiiy theo phep lap kh hoach d6i vox he th6ng MLC nhim muc dich tao cac lieu hdp thu cdn thilt den cac vi tri mong muon tren khoi u.
D6i voi bai mo phong so 2, tu 16 truong chieu xung quanh mo dich ta lira chpn dugc 9 trucmg chieu (hinh 5 ) thoa tieu chi:
- Tao muc lieu cao va dong nhat len khoi u
- Tranh nhihig truong chieu true tiep len cac to chiic nam trong vimg nguy hiem (Thuc te ung dung se sic dung thuat toan toi uu ca ve trucmg chieu va thai gian chieu)
Hinh 5: 16 trudng chiiu co bdn trong bdi todn 2
Kit qua nang lugng hdp thu tren OAR, kh6i u va mo nuac xung quanh thu dugc sau khi chay mo phong nhu sau:
Hgi nghi Khoa hgc vd Cdng nghe hgt nhdn loan quic lin thi IX, Ninh Thudn 18-19/8/2011 563
Colunna I tbcougb 1
4 0 9 1 3 3 4 5 8 2 1 4 0 3 9 7 6 3 6 7 5 5 0 0 8 8 3 7 6 0 9 4 147J
0 3 6 . 7 4 7 4 6 0 5 0 3 7 1 10 I S 2 1
1 5 3 4 0 4 4 9 0 0 6 4 52 Z 7 1 4 7 9 8 0 2 4 4 7 2 3
0 6 1 . 1 9 6 7 62 2 4 3 6 7 12 I S 2 0
9 2 8 2 0 3 9 4 8 2 1 7 1 1 2 4 2 4 2 1 7 2 5 2 6 6 7 3
G 1 8 . 3 1 1 7 5 3 3 0 1 3 J 3 1 1 1 1 1 4
2 8 9 2 BO 67 9 2 4 6 2 9 0 1 5 9 5 7 5 2 6 4 6 4 3 1
0 1 7 . 2 8 8 3 5 8 3 0 1 5 1 3 12 12 1 5
2 5 3 0 S 9 8 2 4 7 2 7 0 3 7 0 0 7 2 8 1 7 7 8 0 5 3 2
b l 6 3 2 5 3 8 7 12 I S 1 8
2 5 0 0 1 1 5 4 9 5 2 7 7 7 3 8 6 1 6 5 2 0 6 9 2 2 3 8 6 1 9 0
3 8 . 3 6 3 8 6 0 . 3 3 7 5 4 9 . 6 4 6 2 3 6 . 7 8 4 8 1 . 3 9 9 5 1 1 . 0 8 7 3 1 7 . 3 7 2 8 2 1 . 8 2 4 7
1 3 . S 2 9 4 5 6 . 0 6 4 9 I 9 . S 9 1 3 3 . 3 7 6 7 2 1 . 3 9 9 7 1 6 . 0 1 0 6 1 6 . 6 1 7 9 1 8 . 6 6 8 0
0 0 0 0 0 . 0 S 0 7 0 . 0 6 2 7 0 , 1 4 6 0 1 . 3 3 6 3
0 0 0 0 7 . 1 D 5 6 8 . 2 1 9 2 1 0 . 1 S 1 4 1 1 . 3 9 5 8
0 0 0 0 5 . 4 6 8 9 1 1 . 6 1 7 8 1 6 . 0 9 5 9 1 9 . 1 4 4 3
0 0 0 0 8 . 4 4 6 4 4 . B 0 7 0 3 . 6 3 0 4 4 . 3 S a 4
0 0 0 0 6 . 6 5 6 5 4 . 9 2 6 1 3 . 6 1 7 7 4 . 4 5 8 3
S.ZSSe 7.0126 0.0126 11.3211 B.84S5 0.0177 14.B640 1O.09S6 0.1341 19.0690 11.7972 1.1627
Ban do phan bo lieu len cac khoi sau khi xir ly ket qua tren va hiln thi bang MATLAB (hinh 6):
Hinh 6: Bdn do phdn bd liiu len cdc khdi
Dua tren ban do lieu thu dugc nhan thdy rdng: d6i voi phep chieu 9 truong lua chpn da thirc hi?n phep chuyen lieu len kbli u phantom muc lilu khoang 60Gy 6 viing giOa cua lop thu 1 va lop thu- 2 cua kbli u, lilu d lop 3 va lap 4 dat dugc kha thdp (dac biet la 6f lop 4, voi muc lieu cao nhat khoang 40Gy). Lilu hip thu len OAR la khoang 27Gy (muc lilu cho phep cho OAR trong truong hgp nay la 30Gy). Day la kit qua rdt tit bed vi dii voi phep chuyen lieu, voi muc dich la chuyin mpt lilu tuong dii ding nhdt Ien khii u, va muc lilu len cac ithoi u phai dat den mpt gia tri mong mu6n nhimg dong thoi lieu Ien cac OAR phai thap hon mpt nguong cho phep.
Bai mo phong so 2 liy theo s6 lieu thoi gian chilu va dang khong gian ciia phantoml trong bai khao sat chilu xa thuc tl bing thilt bi IMRT (hinh 7) [3]. So sanh kit qua bai mo phong sl 2 tinh toan thong qua mo phong bdng PENELOPE va kit qua cua bai khao sat trong phep chilu IMRT cat lap 9 truong co sir tucmg ding cu thi nhu sau:
564 Hdi nghj Khoa hgc vd Cdng nghe hgt nhdn todn qudc idn thuIX, Ninh Thugn 18-19/8/2011
Lieu hap thu toi da ciia OAR trong bai khao sat: 30.3Gy.
Lieu hap thu cua OAR trong bai mo phong so 2: 27.4Gy.
Lieu hdp thu cua khoi u trong bai khdo sat tir 59.3Gy den 73.1Gy.
Lilu hdp thu cua kbli u trong bai mo phong so 2 khoang 60Gy 6 lop khoi u thu 2,
Hinh 7: Anh t hogch Eclipse [3]
Muc dich cua hai bai mo phong tren la su dung cong cy PENELOPE de mo phong phuong phap IMRT tren nhiing mo hinh phantom co ban, ket qua cho thdy:
- Phuong phap IMRT bang each thay doi vj tri cua cac la tren he thong MLC 6 bai toan 1 cho phep dieu bien hinh dang va cuong dp chieu xa ISn bl mdt chilu xa theo nhu hinh dang va mat dp cua khoi u. Tir do chiing minh rang tgi vi tri mpt goc chieu chung ta co the chuyen ' lieu mong muon den cac khoi u da dang ve hinh d^g, kich thuoc.
- IMRT cho phep chieu khoi u duoi nhieu goc dp khac nhau trong khong gian nhu 6 bai toan 2. Bang each ket hgp nhieu goc chieu (nhieu truong chieu) cua lieu phdp cdt lap, vol moi goc chieu iing vai sir dieu bien khac nhau, tit d6 co thi tgo dugc mgt phan bl lilu tii uru len khoi u. 6 phuong phap cat lap, phan bo lieu dugc lira chpn thu cong dua tren mgt sl trucmg chieu chinh voi tieu chi lua chpn sao cho tao ra mure lieu cao vd dong nhdt len kbli u dong thoi ban che cac truong chieu true tiep len OAR nhdm tranh su tao ra lilu cao. Tren thuc tl cac phdn mem may tinh se dugc th\ic hien su lira chpn phan bl lilu tii uu m§t each tu dpng nha vao cac thuat toan phdn bo lieu toi uu phiic tap (chdng hgn thugt toan DAO).
TAI LIEU THAM KHAO
[1]. PENELOPE 2003, a code system for Monte Carlo simulation of electron and photon transport - Francesc Salvat. Facultat de Fisica (ECM), Universitat de Barcelona. Diagonal 647, 08028 Barcelona, Spain.
[2]. S.Webb (2001). Intensity modulated radiation therapy. Publisher lOP
[3]. Mike Oliver, Will Ansbacher, Wayne A. Beckham (2009). Comparing planning time, delivery time and plan quality for IMRT, RapidArc and tomotherapy. Joumal of Applied Clinical Medical Physics, 10, ppl 17-132
