Progress in Medical Physics (한국의학물리학회지:의학물리)

Korean Society of Medical Physics (한국의학물리학회)
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Comparison of Intensity Modulated Radiation Therapy Dose Calculations with a PBC and AAA Algorithms in the Lung Cancer

폐암의 세기조절방사선치료에서 PBC 알고리즘과 AAA 알고리즘의 비교연구

  • Oh, Se-An (Department of Physics, Yeungnam University) ;
  • Kang, Min-Kyu (Department of Radiation Oncology, Yeungnam University College of Medicine) ;
  • Yea, Ji-Woon (Department of Radiation Oncology, Yeungnam University College of Medicine) ;
  • Kim, Sung-Hoon (Department of Radiation Oncology, Yeungnam University College of Medicine) ;
  • Kim, Ki-Hwan (Department of Radiation Oncology, Chungnam National University Hospital) ;
  • Kim, Sung-Kyu (Department of Radiation Oncology, Yeungnam University College of Medicine)
  • 오세안 (영남대학교 이과대학 물리학과) ;
  • 강민규 (영남대학교 의과대학 방사선종양학교실) ;
  • 예지원 (영남대학교 의과대학 방사선종양학교실) ;
  • 김성훈 (영남대학교 의과대학 방사선종양학교실) ;
  • 김기환 (충남대학교병원 방사선종양학과) ;
  • 김성규 (영남대학교 의과대학 방사선종양학교실)
  • Received : 2012.02.03
  • Accepted : 2012.03.03
  • Published : 2012.03.31
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Abstract

The pencil beam convolution (PBC) algorithms in radiation treatment planning system have been widely used to calculate the radiation dose. A new photon dose calculation algorithm, referred to as the anisotropic analytical algorithm (AAA), was released for use by the Varian medical system. The aim of this paper was to investigate the difference in dose calculation between the AAA and PBC algorithm using the intensity modulated radiation therapy (IMRT) plan for lung cancer cases that were inhomogeneous in the low density. We quantitatively analyzed the differences in dose using the eclipse planning system (Varian Medical System, Palo Alto, CA) and I'mRT matirxx (IBA, Schwarzenbruck, Germany) equipment to compare the gamma evaluation. 11 patients with lung cancer at various sites were used in this study. We also used the TLD-100 (LiF) to measure the differences in dose between the calculated dose and measured dose in the Alderson Rando phantom. The maximum, mean, minimum dose for the normal tissue did not change significantly. But the volume of the PTV covered by the 95% isodose curve was decreased by 6% in the lung due to the difference in the algorithms. The difference dose between the calculated dose by the PBC algorithms and AAA algorithms and the measured dose with TLD-100 (LiF) in the Alderson Rando phantom was -4.6% and -2.7% respectively. Based on the results of this study, the treatment plan calculated using the AAA algorithms is more accurate in lung sites with a low density when compared to the treatment plan calculated using the PBC algorithms.

방사선치료계획장치에서 선량계산을 위해 PBC 알고리즘(pencil beam convolution)은 가장 널리 사용되고 있다. Varian (Varian Medical System, Palo Alto, CA)사는 광자의 선량 계산을 위해서 AAA 알고리즘을 새롭게 선량계산모델로 탑재하였다. 본 연구는 폐와 같은 저밀도 영역에 종양부위가 있는 환자를 대상으로 세기조절방사선치료를 시행할 경우에 PBC 알고리즘과 AAA 알고리즘으로 계산했을 때 차이를 정량적으로 알고자 하는데 목적이 있다. 두 알고리즘의 정량적 분석을 위해서 Eclipse planning system과 I'mRT matrixx (IBA, Schwarzenbruck, Germany)를 사용하였다. 또한 두 알고리즘으로 계산된 선량과 실제 측정된 선량의 차이를 확인하기 위해서 인체모형펜텀(Alderson Rando phantom)속에 TLD-100 (LiF)을 위치 시켰다. 종양부위 주위의 중요장기인 trachea, esophagus, lung, PRV spinal cord의최대선량, 평균선량, 최소선량은 알고리즘의 변화에 따라서 거의 변화가 없었으나, PTV의 V95는 PBC와 비교하여 AAA가 약 6% 감소하는 결과를 얻었다. 이러한 결과는 I'mRT matrixx를 이용하여 저밀도를 가지는 폐의 위치에서 확연하게 나타남을 확인할 수 있었다. 또한 인체모형펜텀(Alderson Rando phantom)과 TLD-100 (LiF)을 이용한 계산선량과 실제 측정치의 결과는 PBC 알고리즘은 평균 4.6%의 차이를 보였으며, AAA 알고리즘은 평균 2.7%의 차이를 보였다. 이 결과로 저밀도를 가지는 폐암에서의 세기조절방사선치료를 시행할 경우에 PBC 알고리즘보다 AAA 알고리즘이 더 유효함을 알 수 있다.

Keywords

References

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