The Journal of Korean Society for Radiation Therapy (대한방사선치료학회지)

Korean Society for Radiation Therapy (대한방사선치료학회)
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A Study of volumetric modulated arc therapy for stereotactic body radiation therapy in case of multi-target liver cancer using flattening filter free beam

다중표적 간암의 정위적체부방사선치료에서 무편평화여과기선질 용적변조회전치료의 유용성 평가

  • Yeom, Misuk (Department of Radiation Oncology, ASAN Medical Center) ;
  • Yoon, Inha (Department of Radiation Oncology, ASAN Medical Center) ;
  • Hong, Donggi (Department of Radiation Oncology, ASAN Medical Center) ;
  • Back, Geummun (Department of Radiation Oncology, ASAN Medical Center)
  • 염미숙 (서울아산병원 방사선종양학과) ;
  • 윤인하 (서울아산병원 방사선종양학과) ;
  • 홍동기 (서울아산병원 방사선종양학과) ;
  • 백금문 (서울아산병원 방사선종양학과)
  • Received : 2015.04.14
  • Accepted : 2015.06.24
  • Published : 2015.06.30
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Abstract

Purpose : Stereotactic body radiation therapy (SBRT) has proved its efficacy in several patient populations with primary and metastatic limited tumors. Because SBRT prescription is high dose level than Conventional radiation therapy. SBRT plan is necessary for effective Organ at risk (OAR) protection and sufficient Planning target volume (PTV) dose coverage. In particular, multi-target cases may result excessive doses to OAR and hot spot due to dose overlap. This study evaluate usefulness of Volumetric modulated arc therapy (VMAT) in dosimetric and technical considerations using Flattening filter free (FFF) beam. Materials and Methods : The treatment plans for five patients, being treated on TrueBeam STx(Varian$^{TM}$, USA) with VMAT using 10MV FFF beam and Standard conformal radiotherapy (CRT) using 15MV Flattening filter (FF) beam. PTV, liver, duodenum, bowel, spinal cord, esophagus, stomach dose were evaluated using the dose volume histogram(DVH). Conformity index(CI), homogeneity index(HI), Paddick's index(PCI) for the PTV was assessed. Total Monitor unit (MU) and beam on time was assessed. Results : Average value of CI, HI and PCI for PTV was $1.381{\pm}0.028$, $1.096{\pm}0.016$, $0.944{\pm}0.473$ in VMAT and $1.381{\pm}0.042$, $1.136{\pm}0.042$, $1.534{\pm}0.465$ in CRT respectively. OAR dose in CRT plans evaluated 1.8 times higher than VMAT. Total MU in VMAT evaluated 1.3 times increase than CRT. Average beam on time was 6.8 minute in VMAT and 21.3 minute in CRT. Conclusion : VMAT for SBRT in multi-target liver cancer using FFF beam is effective treatment techniqe in dosimetric and technical considerations. VMAT decrease intra-fraction error due to treatment time shortening using high dose rate of FFF beam.

목 적 : 정위적체부방사선치료(Stereotatic body radiation therapy, SBRT)는 원발성 종양과 전이성 종양의 치료법으로 이용되어진다. SBRT는 높은 선량을 전달하기 때문에 MU(Monitor unit)의 증가로 치료시간이 길어지고 치료계획용적(Planning Target Volume, PTV) 주변의 정상장기를 효과적으로 보호할 수 있는 치료계획이 필요하다. 특히 다중표적의 경우 SBRT를 여러 번에 나누어 치료해야하거나 선량 겹침으로 인한 고 선량 영역(Hot spot)이 생길수도 있다. 본 연구는 다중표적 간암에서 TrueBeam STx(Varian, USA)의 무편평화여과기선질(Flattening filter free, FFF) beam을 이용한 용적변조회전치료(Volumetric modulated arc therapy, VMAT)의 유용성을 평가하고자 한다. 대상 및 방법 : 다중표적 간암의 SBRT를 시행하는 5명의 환자를 대상으로 TrueBeam STx의 10MV FFF beam을 이용한 VMAT과 15MV 편평화여과기선질(Flattening filter, FF) beam을 이용한 입체조형치료(conformal radiotherapy, CRT)계획을 세웠다. 두 치료계획을 비교하기 위하여 선량용적히스토그램(Dose Volume Histogram, DVH)을 이용하여 치료계획용적(Planning Target Volume, PTV), 간, 십이지장, 장, 식도, 척수에 들어가는 선량을 평가하고 전체 MU 값을 비교하였다. 또한 두 치료계획의 치료시간을 비교하기 위하여 Beam on time을 평가하였다. 결 과 : PTV에 대한 처방선량지수(Conformity Index, CI), 선량균질지수(Homogeneity index, HI), 처방선량포함지수(Paddick's Conformity Index, PCI)의 평균값은 VMAT에서 각각 $1.006{\pm}0.028$, $1.098{\pm}0.016$, $1.132{\pm}0.084$, CRT에서 $1.381{\pm}0.419$ $1.136{\pm}0.042$, $1.534{\pm}0.465$로 평가되었다. 정상장기에 대한 선량은 CRT에서 VMAT 보다 약 1.8배 높은 선량으로 평가되었다. 전체 MU값은 VMAT에서 약 1.3배 높게 평가되었고 VMAT과 CRT 두 치료계획의 평균 Beam on time은 각각 6.8분, 21.3분으로 평가되었다. 결 론 : 다중표적 간암의 정위적체부방사선치료에서 FFF Beam을 이용한 VMAT을 적용하면 선량 겹침 없이 다중표적을 한 번에 치료할 수 있으며 PTV의 선량포함을 만족하면서 주위의 정상장기를 더 효과적으로 보호할 수 있는 치료계획이 가능하다. 또한 FFF Beam의 높은 선량률(Dose rate)을 이용하여 치료시간을 단축시켜 치료 중 발생할 수 있는 오차를 감소시킬 수 있다.

Keywords

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