Panettieri Vanessa, Wennberg Berit, Gagliardi Giovanna, Duch Maria Amor, Ginjaume Mercè, Lax Ingmar
Institut de Tècniques Energètiques, Universitat Politècnica de Catalunya, Diagonal 647, 08028 Barcelona, Spain.
Phys Med Biol. 2007 Jul 21;52(14):4265-81. doi: 10.1088/0031-9155/52/14/016. Epub 2007 Jun 20.
The purpose of this work was to simulate with the Monte Carlo (MC) code PENELOPE the dose distribution in lung tumours including breathing motion in stereotactic body radiation therapy (SBRT). Two phantoms were modelled to simulate a pentagonal cross section with chestwall (unit density), lung (density 0.3 g cm(-3)) and two spherical tumours (unit density) of diameters respectively of 2 cm and 5 cm. The phase-space files (PSF) of four different SBRT field sizes of 6 MV from a Varian accelerator were calculated and used as beam sources to obtain both dose profiles and dose-volume histograms (DVHs) in different volumes of interest. Dose distributions were simulated for five beams impinging on the phantom. The simulations were conducted both for the static case and including the influence of respiratory motion. To reproduce the effect of breathing motion different simulations were performed keeping the beam fixed and displacing the phantom geometry in chosen positions in the cranial and caudal and left-right directions. The final result was obtained by combining the different position with two motion patterns. The MC results were compared with those obtained with three commercial treatment planning systems (TPSs), two based on the pencil beam (PB) algorithm, the TMS-HELAX (Nucletron, Sweden) and Eclipse (Varian Medical System, Palo Alto, CA), and one based on the collapsed cone algorithm (CC), Pinnacle(3) (Philips). Some calculations were also carried out with the analytical anisotropic algorithm (AAA) in the Eclipse system. All calculations with the TPSs were performed without simulated breathing motion, according to clinical practice. In order to compare all the TPSs and MC an absolute dose calibration in Gy/MU was performed. The analysis shows that the dose (Gy/MU) in the central part of the gross tumour volume (GTV) is calculated for both tumour sizes with an accuracy of 2-3% with PB and CC algorithms, compared to MC. At the periphery of the GTV the TPSs overestimate the dose up to 10%, while in the lung tissue close to the GTV PB algorithms overestimate the dose and the CC underestimates it. When clinically relevant breathing motions are included in the MC simulations, the static calculations with the TPSs still give a relatively accurate estimate of the dose in the GTV. On the other hand, the dose at the periphery of the GTV is overestimated, compared to the static case.
这项工作的目的是使用蒙特卡罗（MC）代码PENELOPE模拟立体定向体部放射治疗（SBRT）中肺部肿瘤的剂量分布，包括呼吸运动。构建了两个体模来模拟具有胸壁（单位密度）、肺（密度0.3 g/cm³）以及两个直径分别为2 cm和5 cm的球形肿瘤（单位密度）的五边形横截面。计算了来自瓦里安加速器的四种不同6 MV SBRT射野尺寸的相空间文件（PSF），并将其用作束源，以获取不同感兴趣体积内的剂量分布曲线和剂量体积直方图（DVH）。模拟了五束射线照射体模的情况。模拟既针对静态情况进行，也考虑了呼吸运动的影响。为了再现呼吸运动的效果，进行了不同的模拟，保持射线固定，在头脚方向和左右方向将体模几何形状移动到选定位置。通过将不同位置与两种运动模式相结合得到最终结果。将MC结果与使用三种商业治疗计划系统（TPS）获得的结果进行比较，其中两种基于笔形束（PB）算法，即TMS-HELAX（瑞典核通公司）和Eclipse（瓦里安医疗系统公司，加利福尼亚州帕洛阿尔托），另一种基于坍缩圆锥算法（CC），即Pinnacle(3)（飞利浦公司）。在Eclipse系统中还使用解析各向异性算法（AAA）进行了一些计算。根据临床实践，所有使用TPS的计算均未模拟呼吸运动。为了比较所有TPS和MC，进行了Gy/MU的绝对剂量校准。分析表明，与MC相比，对于两种肿瘤大小，使用PB和CC算法计算的大体肿瘤体积（GTV）中心部分的剂量（Gy/MU）精度为2% - 3%。在GTV周边，TPS高估剂量高达10%，而在靠近GTV的肺组织中，PB算法高估剂量，CC算法低估剂量。当MC模拟中包含临床相关的呼吸运动时，使用TPS的静态计算仍能相对准确地估计GTV中的剂量。另一方面，与静态情况相比，GTV周边的剂量被高估。
