Journal of Radiation Industry 12 (1) : 51 ~ 56 (2018) Technical Paper 용적변조회전방사선치료시 Set-up 오차에따른선량전달정확성의평가 하광은 2 나권우 1 이주훈 1 박성아 1 김상현 1, * 1 신한대학교방사선학과, 2 을지대학교병원방사선종양학과 Assessment of Dose Delivery Accuracy with Set-up Error for VMAT Gwang-Eun Ha 2, Kwon-Ou Na 1, Ju-Hun Lee 1, Sung-Ah Park 1 and Sang-Hyun Kim 1, * 1 Department of Radiological Science, Shinhan University, 95, Hoam-ro, Uijeongbu-si, Gyeonggi-do 11644, Republic of Korea 2 Department of Radiation Oncology, EulJi Hospital, 68, Hangeulbiseok-ro, Nowon-gu, Seoul 01830, Republic of Korea Abstract - In order to investigate the effect of set-up error on the dose delivery, this study evaluates the accuracy of dose delivery due to set-up error by applying a virtual brain tumor treatment plan using volumetric modulated rotational radiation therapy (VMAT). After obtaining a crosssectional image with a CT device using Head Phantom, a treatment planning program was used to establish a VMAT treatment plan. Based on the treatment plan established, DQA was performed to assess the difference in dose delivery accuracy with set-up error. When the distance was changed to 7 mm with a distance of 1 mm on the basis of the measured value of 0 in the direction of Lat. and Vrt, a comparison was performed by deriving the average after 5 measurements each using a three dimensional array detector. We applied a virtual brain tumor treatment plan using VMAT. In the absence of set-up error, the measured values were 96.8%, 96.4%, 96.2% in Lat. ±1 mm, 96.2%, 95.9% in Lat. ±2 mm, 95.4%, 95.2% in Lat. ±3 mm, 92.0%, 90.1% in Lat. ±4 mm, 86.9%, 83.7% in Lat. ±5 mm, 85.6%, 80.3% in Lat. ±6 mm, 75.2%, 79.5% in Lat.±7 mm, respectively. 96.1%, 96.1% in Vrt. ±1 mm, 95.9%, 95.7% in Vrt. ±2 mm, 95.1%, 95.1% in Vrt. ±3 mm, 91.4%, 91.5% in Vrt. ±4 mm, 88.6%, 88.3% in Vrt. ±5 mm, 83.1%, 85.6% in Vrt. ±6 mm, 79.1%, 77.2% in Vrt. ±7 mm respectively. As the lateral and vertical error increases, the accuracy of the dose delivery decreases. In order to improve the accuracy of the dose delivery during VMAT treatment, we should try to reduce the error through accurate posture and appropriate image induction. Key words : VMAT, Gamma index, 3D array detecter, Set-up error 서 일반적인 2 차원방사선치료를비롯하여 3 차원입체조형 방사선치료, 세기조절방사선치료, 최근의용적변조회전방 론 * Corresponding author: Sang-Hyun Kim, Tel. +82-31-870-3413, Fax. +82-31-870-3419, E-mail. kbm0821@shinhan.ac.kr 사선치료및영상유도방사선치료에이르기까지방사선치료기술은지속적인발전을이루고있다 (Bak et al. 2006; Bruno and Aris 2006). 이러한첨단방사선치료법들은공통적으로종양부위에처방선량을집중하고주위의정상조직및중요장기에피폭되는선량을줄이는데목적을두고있다. 즉, 조사야마진 (margin) 을줄여종양에조사하는선량 51
52 하광은 나권우 이주훈 박성아 김상현 Fig. 1. Head phantom and baseplates. Fig. 3. ArcCHECK. Fig. 2. Head phntom and big bore CT. Fig. 4. ArcCHECK and synergy. 을증가시켜치료효과를높이고, 주위의정상조직과중요장기의부작용이나합병증을감소시킴으로써결국에는보다나은치료결과를얻고자하는것이다. 그중기존의방사선치료가특정방향에서만고정되어서방사선의조사가이루어졌던것과는달리용적변조회전방사선치료는세기조절방사선치료 (IMRT) 를하면서치료기가환자주위를 360 도회전하는동안 Beam을조사하는방식으로선형가속기의회전속도와선량률까지연속적으로조절가능하다. 그러므로주변정상조직으로조사되는방사선량을최소화하면서종양에만계획한방사선량이전달되도록하여, 부작용을최소화하고높은치료효과를얻을수있다 (Lee et al. 2013; Kim et al. 2016). 방사선치료에서환자의 Set-up 과정, 혹은환자의움직임이원인이되어발생하는 Set-up 오차등은첨단치료의장점을경감시키는가장중요한요인중하나이다 (Kim et al. 2007). 다시 Set-up을해야하는번거로움을줄여줄수있으며, 실제보정된수치도직접확인할수있게되었다 (Guckenberger et al. 2012). 만약 Set-up 오차를보정하지않고치료를하게되는경우치료계획용적 (Planning Target Volume, PTV) 에저선량전달및주변주요장기에과한선량전달의결과를초래할가능 성도있다 (Holtzer et al. 2012). 이러한경우환자의 Set-up 을다시실시한후오차를보정하여치료를진행하고있다. 본논문에서는가상의뇌종양치료시발생하는 Lateral과 Vertical에대한치료오차의보정이이루어지지않은상태에서치료가진행되었을경우, 실제조사되는선량전달정확성을평가해보고자한다. 재료및방법 1. 실험재료 Head Phantom (The Standard Model 038 CRIS, USA) 과고정용구로 Baseplates (Standard Supine Uni-fame CIVCO, USA) 를사용하였다 (Fig. 1). Big bore CT (Philips Medical Systems, Netherlands) 를사용하였으며 (Fig. 2), 치료검증장비로 ArcCHECK (Sun Nuclear, USA) 를사용하였다 (Fig. 3). 장비는 Synergy (Elekta Medical Systems, Sweden) 를사용하였고 (Fig. 4), 용적변조회전방사선치료계획프로그램은 MONACO 3.3 (Elekta Medical Systems, Sweden), FocalSim 4.8 (Elekta Medical Systems, Sweden), MOSAIQ 2.6 (Elekta
Set-up 오차에따른선량전달정확성평가 53 Fig. 5. Radiation therapy planning with MONACO 3.3. Medical Systems, Sweden) 를사용하였다 (Fig. 5). 용적변조회전방사선치료선량분석프로그램은 SNC Patient 6.1 (Sun Nuclear, USA) 을사용하였다. 2. 실험방법 Elekta 사의 Synergy, 그리고 6 MV의광자선이사용되었다. CRIS 사의 Head Phantom과 CIVCO 사의 Baseplates를사용하여 Philips 사의 Big bore CT로촬영하고단면영상을획득한후, Elekta 사의 MONACO를이용하여 control point 는 150개이하로제한하였고, 방사선량계산간격은 3 mm 로, couch와 col. 는 0도로고정하여 VMAT 치료계획을하였다. 실험에는용적변조회전방사선치료치료계획을사용한가상의뇌종양치료계획을적용하였다. 전산화치료계획시스템을이용하여환자의치료계획정보를품질관리용치료계획으로변환하고원통형 3차원배열검출기 ( 전리함수 : 1,386개, 검출기용적 : 0.019 mm 3, 직경 : 21.0 cm, 높이 : 21.0 cm, 배열간격 : 1.0 cm, 배열방법 : 나선형 ) 를사용하여각각의조건에서측정하였다. 이동이없는 No 일때를기준으로하여임의의간격 (±1 7 mm) 을 Lateral과 Vertical 방향으로각 1 mm 간격으로이동하여각각평균 5회선량측정을하였다 (Lat. 시 + 는우측, - 는좌측을뜻하며, Vrt. 시 + 는상방, - 는하방을뜻한다 ). 각조건에서측정된선량분포의차이를분석하기위해용적변조회전방사선치료분석프로그램 SNC Patient를사용하였으며거리상의일치 (distance-to-agreement DTA) 와선량에대한차이 (Dose difference, DD) 에대하여이원화된정량적평가방법인감마지수 (Gamma Index) 를이용하였다 (Francisco et al. 2011; Stock et al. 2011; Stasi et al. 2012). 결과 1. Lateral 방향 setup 오차에의한감마지수 Setup 오차가없을때 (No ) 측정값은 96.8% 로나타났고 Lateral + 방향으로 1 mm 이동시에는각각 96.4%, 96.3%, 96.3%, 96.4%, 96.5%, - 방향에서는 96.1%, 96.2%, 96.2%, 96.2% 96.1% 의값을획득하였다. 2 mm 이동시에는 + 방향에서각각 96.0%, 96.2%, 96.3%, 96.2%, 96.2%, - 방향에서는 95.9%, 96.0%, 95.7%, 96.0%, 95.9% 의값을획득하였다. 3 mm 이동시에는 + 방향에서각각 95.3%, 95.4%, 95.5%, 95.3%, 95.5%, - 방향에서는 95.2%, 95.2%, 95.1%, 95.1%, 95.2% 의값을획득하였다. 4 mm 이동시에는 + 방향에서각각 92.2%, 91.9%, 91.9%, 92.0%, 92.0%, - 방향에서는 90.1%, 90.1%, 90.0%, 90.1%, 90.1% 의값을획득하였다. 5 mm 이동시에는 + 방향에서각각 86.8%, 87.0%,
54 하광은 나권우 이주훈 박성아 김상현 Table 1. Analysis of dose delivery (Lateral right) 1 96.4 96.3 96.3 96.4 96.5 96.38±0.08 2 96.0 96.2 96.3 96.2 96.2 96.18±0.10 3 95.3 95.4 95.5 95.3 95.5 95.40±0.10 4 92.2 91.9 91.9 92.0 92.0 92.00±0.12 5 86.8 87.0 86.9 86.9 86.9 86.90±0.07 6 85.5 85.5 85.8 85.6 85.6 85.60±0.12 7 79.5 79.7 79.5 79.5 79.5 79.54±0.08 Table 4. Analysis of dose delivery (Vertical inferior) 1 96.2 96.1 96.2 96.0 96.1 96.12±0.08 2 95.7 95.7 95.6 95.7 95.8 95.70±0.07 3 95.1 95.1 95.1 95.2 95.1 95.12±0.04 4 91.5 91.4 91.4 91.6 91.5 91.48±0.08 5 88.4 88.2 88.2 88.4 88.4 88.32±0.10 6 85.6 85.6 85.6 85.6 85.5 85.58±0.04 7 79.0 79.2 79.2 79.1 79.3 79.16±0.11 Table 2. Analysis of dose delivery (Lateral left) 1 96.1 96.2 96.2 96.2 96.1 96.16±0.05 2 95.9 96.0 95.7 96.0 95.9 95.90±0.12 3 95.2 95.2 95.1 95.1 95.2 95.16±0.05 4 90.1 90.1 90.0 90.1 90.1 90.08±0.04 5 83.7 83.7 83.6 83.7 83.8 83.70±0.07 6 80.3 80.2 80.4 80.3 80.3 80.30±0.07 7 75.1 75.3 75.3 75.1 75.2 75.20±0.10 Table 5. P-value of statistics Lateral Vertical Right Left Superior Inferior 1 0.043 0.042 0.042 0.042 2 0.034 0.043 0.043 0.043 3 0.042 0.043 0.042 0.043 4 0.042 0.042 0.041 0.043 5 0.042 0.043 0.042 0.041 6 0.041 0.039 0.039 0.042 7 0.042 0.042 0.042 0.042 Table 3. Analysis of dose delivery (Vertical superior) 86.9%, 86.9%, 86.9%, - 방향에서는 83.7%, 83.7%, 83.6%, 83.7%, 83.8% 의값을획득하였다. 6 mm 이동시에는 + 방 향에서각각 85.5%, 85.5%, 85.8%, 85.6%, 85.6%, - 방향 에서는 80.3%, 80.2%, 80.4%, 80.3%, 80.3% 의값을획득 하였다. 7 mm 이동시에는 + 방향에서각각 79.5%, 79.7%, 79.5%, 79.5%, 79.5%, - 방향에서는 75.1%, 75.3%, 75.3%, 75.1%, 75.2% 의값을획득하였다. 1 96.0 96.2 96.1 96.1 96.1 96.10±0.07 2 96.0 96.1 95.8 95.9 95.8 95.95±0.13 3 95.2 95.1 95.0 95.1 95.1 95.10±0.07 4 91.5 91.3 91.5 91.3 91.4 91.40±0.10 5 88.5 88.6 88.6 88.6 88.7 88.60±0.07 6 83.0 83.0 83.1 83.2 83.2 83.10±0.10 7 77.1 77.2 77.1 77.3 77.2 77.18±0.08 95.0%, 95.1%, 95.1% 를, -3 mm 방향에서는 95.1%, 95.1%, 95.1%, 95.2%, 95.1% 를획득하였다. +4 mm 방향에서각각 91.5%, 91.3%, 91.5%, 91.3%, 91.4% 를, -4 mm 방향에서는 91.5%, 91.4%, 91.4%, 91.6%, 91.5% 를획득하였다. +5 mm 방향에서각각 88.5%, 88.6%, 88.6%, 88.6%, 88.7% 를, -5 mm 방향에서는 88.4%, 88.2%, 88.2%, 88.4%, 88.4% 를획득하였다. +6 mm 방향에서각각 83.0%, 83.0%, 83.1%, 83.2%, 83.2% 를, -6 mm 방향에서는 85.6%, 85.6%, 85.6%, 85.6%, 85.5% 를획득하였다. +7 mm 방향에서각각 77.1%, 77.2%, 77.1%, 77.3%, 77.2% 를, -7 mm 방향에서는 79.0%, 79.2%, 79.2%, 79.1%, 79.3% 를획득하였다. 3. Setup 오차방향별통계분석비모수검정인 Wilcoxon 부호순위검정을이용하여 setup 오차가없을시에 96.8의평균값을기준으로각경우별 p-value 값을구하였다. Lateral과 Vertical 모두 p<0.05로통계적으로유의하였다. 2. Vertical 방향 setup 오차에의한감마지수 Vertical 방향의이동시에는 +1 mm 방향에서각각 96.0%, 96.2%, 96.1%, 96.1%, 96.1%, -1 mm 방향에서는 96.2%, 96.1%, 96.2%, 96.0%, 96.1% 의값을획득하였다. +2 mm 방향에서는각각 96.0%, 96.1%, 95.8%, 95.9%, 95.8% 를, -2 mm 방향에서는 95.7%, 95.7%, 95.6%, 95.7%, 95.8% 를획득하였다. +3 mm 방향에서각각 95.2%, 95.1%, 고찰가상환자의뇌종양치료시 Lateral, Vertical 방향에서 3 mm Set-up 오차까지는기준치인 95% 를넘어섰지만각 4, 5, 6, 7 mm로오차를둔경우에는현재 ICRU-52에서기준으로하고있는감마지수 (3 mm, 3%, gamma pass rate 95%
Set-up 오차에따른선량전달정확성평가 55 이상 ) 를만족시키지못하였고모든감마지수의유의확률은 p-value 값이 0.05 이하의값이도출되어통계적으로유의하였다. 감마지수 (3 mm, 3%, gamma pass rate 95% 이상 ) 는허용오차범위안에들어왔으나, 선량차이에대해서는간과할수없다. 선행연구에서도 p-value는 95% 신뢰구간에서 0.05 미만으로대립가설이채택되어통계학적으로유의한차이가발생하고이는정확한일치가아닐수있다 (Lee et al. 2013). 중요한조직이나기관으로이루어진머리부위의치료를상정하고평가를하였기에실제뇌종양치료시에는주변주요장기에더큰영향을미칠것이라생각되며, 만약환자에게서발생한오차를간과하고지나치게된다면정밀하게방사선이조사되는용적변조회전방사선치료에서선량전달의정확성측면에부정적인영향을미치게될것이라예상된다. 치료기의복잡한움직임이많아지고치료시선량이세기변조방사선치료에비해큰 VMAT 치료를구현하는데있어서치료장비가계획된치료계획을얼마나정확하게환자에게구현해낼것인지에대한평가, 즉치료전선량평가의중요성이증가하게되었다 (Kim et al. 2016). Set-up 오차를 7 mm 발생을가정한연구는다소무리가있을수있다고생각되어지나선행연구에서보면 21명을대상으로치상돌기 (dens) 의좌우위치변화를측정한결과 2.7% 에서 5 mm 이상에서오차가나타나이를방사선치료계획용프로그램을이용하여재현해보았을때, 임상표적체적의선량조사감소와척수의과도한선량조사가이루어진것으로나타났다 (Kim et al. 2011). 본논문의측정은 Lateral과 Vertical 방향으로의위치변화에따른상황만을상정하여선량측정을실시함으로써 Rotation 변화에따른선량변화는확인할수없었다는한계가있다. 이를보완하기위해추후 Longitudinal 방향과 Pitch, Roll, Yaw의 Rotation 변화가가능한 6D Couch를이용하여추가적인측정및연구를하는것이필요하다고생각된다. 흉 복부에위치한내부장기는환자의호흡에따라위치가변화하기때문에치료계획용표적체적결정시장기의움직임을고려하여확장하게되는데, 이는종양에인접한정상조직이받는선량이증가되어부작용을발생시키게된다. 이에가상의뇌종양만을대상으로하였기에다른부위의치료계획에대해서도연구를할필요가있다고판단된다. 결론본논문의결론은다음과같다. 첫째 Lateral 방향 setup 오차에의한감마지수는오른쪽, 왼쪽이동에서모두 3 mm 이내에서 95% 이상으로측정되었다. 둘째 Vertical 방향 setup 오차에의한감마지수는상, 하이동에서모두 3 mm 이내에서 95% 이상으로측정되었다. 결과에서확인된것처럼환자자세잡이시에나타나는오차의발생에대하여인지하고있을필요가있겠으며, 용적변조회전방사선치료시선량전달의정확성을높이기위해서는정확한자세잡이와영상유도를통하여 Set-up 오차가발생했을경우, 이를다시바로잡아오차를줄이도록노력해야한다. 두경부암은조직이나기관이복잡한구조를가지고있어치료에어려움이있다. 척수, 시신경교차점, 척수등중요정상기관이표적과근접해있으면서계획용표적체적의여유마진이작아서환자자세잡이오차가중요하다. VMRT 치료는종양주변의임계장기에적은선량을부여하고종양에는더큰선량을줌으로써치료효과를높이는효과적인치료법이다. 이에환자자세잡이를줄이는노력을한다면방사선을이용한치료목표인정상조직의장해확률을가능한작게하고, 종양조직에더큰선량을증가시킴으로써종양치유확률을증가시킬수있다. 참고문헌 Bak J, Jeong K, Keum KC and Park SW. 2006. On-line Image Guided Radiation Therapy using Cone-beam CT (CBCT). J. Korean. Soc. Ther. Radiol. Oncol. 24(3):294-299. Bruno S and Aris T. 2006. Clinical application of image-guided radiotherapy, IGRT (on the Varian OBI platform). Cancer Radioth. 10(5):252-257. Francisco CH and Silvia VC 2011. A Probability Approach to the Study on Uncertainty Effects on Gamma Index Evaluations in Radiation Therapy. Int. J. Comput. Math. 2011 (Article ID 861869):1-10. Guckenberger M, Roesch J, Baier K, Sweeney RA and Flentje M. 2012. Dosimetric consequences of translation and rotational errors in frame-less image-guided radiosurgery. Radiat. Oncol. 7(1):1-8. Holtzer N, Hoffmans D, Dahele M, Cuijpers JP, Slotman BJ and Verbakel WF. 2012. Roll and Pitch Correction in Headand-Neck Patients by Rapid Adaptation of Volumetric Modulated Arc Treatment Plans. Int. J. Radiat. Oncol. Biol. Phys. 84(3): S28-S29. Hussein M and Rowshanfarzad P. 2013. A comparison of the gamma index analysis in various commercial IMRT/VMAT QA systems. Radiother. Oncol. 109(3):370-376. Kim DH, Kim YT, Ki YG, Nam JH and Lee MR. 2011. Location error od the in a two-dimensional set-up verification during head and neck radiotherapy. J. Korean. Soc. Ther. Radiol. Oncol. 29(2):107-114. Kim JD, Lee HO, You JM, Ji DH and Song JY. 2007. Analyses
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