COLLAPSED CONE CONVOLUTION OF RADIANT ENERGY FOR PHOTON DOSE CALCULATION IN HETEROGENEOUS MEDIA
COLLAPSED CONE CONVOLUTION OF RADIANT ENERGY FOR PHOTON DOSE CALCULATION IN HETEROGENEOUS MEDIA
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DOI：
10.1118/1.596360
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发表时间：
1989-07-01
期刊：
影响因子：
3.8
通讯作者：
AHNESJO, A
中科院分区：
文献类型：
--
作者：
AHNESJO, A
本文介绍了一种计算光子束剂量的方法。通过患者对初级光子束进行射线追踪，并计算释放到患者体内的总辐射能量的分布。多能能量沉积内核计算从光束的光谱，使用单能内核的数据库。结果表明，多能核可以用{Aexp（-ar）+ B exp（-br）}/r ~ 2精确地描述，其中A，a，B，B依赖于入射光子的角度和加速势，r是径向距离. A、a、B和B的数值被导出并用于卷积能量沉积核与每单位质量释放的总能量（TERMA）以产生剂量分布。卷积是faciliated通过引入的崩溃锥近似。在这种近似中，所有从锥体轴上的体积元素释放到等立体角的同轴锥体中的能量都被直线地传输、衰减并沉积在轴上的元素中。在卷积过程中隐式地进行核的缩放，以充分考虑照射体积中存在的不均匀性。使用该方法计算剂量所需的计算操作的数量与计算点的数量成比例。该方法进行了测试的五个加速电位; 4，6，10，15，和24 MV，并施加到两个几何形状;一个是一堆厚片的组织介质，另一个是一个纵隔样的软木和水的幻影。在这些几何形状中，EGS 4 Monte Carlo系统已被用来生成参考剂量分布，与塌陷锥卷积方法计算的剂量进行比较。一般来说，这些方法之间的一致性非常好。然而，在低密度介质中的带电粒子横向不平衡的情况下，观察到的偏差，但其结果是上级相比，广义的Brachio方法。
A method for photon beam dose calculations is described. The primary photon beam is raytraced through the patient, and the distribution of total radiant energy released into the patient is calculated. Polyenergetic energy deposition kernels are calculated from the spectrum of the beam, using a database of monoenergetic kernels. It is shown that the polyenergetic kernels can be analytically described with high precision by {A exp(-ar) + B exp(-br)}/r2, where A, a, B, and b depend on the angle with respect to the impinging photons and the accelerating potential, and r is the radial distance. Numerical values of A, a, B, and b are derived and used to convolve energy deposition kernels with the total energy released per unit mass (TERMA) to yield dose distributions. The convolution is faciliated by the introduction of the collapsed cone approximation. In this approximation, all energy released into coxial cones of equal solid angle, from volume elements on the cone axis, is rectilinearly transported, attenuated, and deposited in elements on the axis. Scaling of the kernels is implicity done during the convolution procedure to fully account for inhomogeneities present in the irradiated volume. The number of computational operations needed to compute the dose with the method is proportional to the number of calculation points. The method is tested for five accelerating potentials; 4, 6, 10, 15, and 24 MV, and applied to two geometries; one is a stack of slabs of tissue media, and the other is a mediastinum-like phantom of cork and water. In these geometries, the EGS4 Monte Carlo system has been used to generate reference dose distributions with which the dose computed with the collapsed cone convolution method is compared. Generally, the agreement between the methods is excellent. Deviations are observed in situations of lateral charged particle disequilibrium in low density media, however, but the result is superior compared to that of the gneralized Batho method.