A finite size pencil beam for IMRT dose optimization
A finite size pencil beam for IMRT dose optimization
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DOI：
10.1088/0031-9155/50/8/009
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发表时间：
2005-04-21
影响因子：
3.5
通讯作者：
Alber, M
中科院分区：
文献类型：
--
作者：
Jelen, U;Söhn, M;Alber, M
使用小射野元素（小射束）的强度调制放射治疗（IMRT）的剂量优化需要计算大量非常小的、通常仅虚拟的、通常尺寸为几mm至1 em的射野。合适的剂量计算算法的主要要求是（1）速度和（2）适当考虑由这些子射束组成的射野的半影。在这里，提出了一种有限尺寸笔形射束（fsPB）算法，该算法是专门为基于小射束的调强放射治疗而设计的。该算法采用了一个分析函数的交叉剖面的子光束，这是基于假设的自我一致性，即要求的任意叠加邻接的子光束应该加起来均匀的字段。深度依赖性存储在从蒙特卡罗计算的剂量分布导出的表中。实验证明，该算法可以准确地生成典型多叶形状段的输出因子和横剖面。由于精确的半影模型，剂量分布在迭代优化的任何阶段都具有物理上可行的梯度，这消除了由于优化和重新计算的治疗计划之间的梯度未对准而导致的正常组织剂量的大差异问题。
Dose optimization for intensity modulated radiotherapy (IMRT) using small field elements (beamlets) requires the computation of a large number of very small, often only virtual fields of typically a few mm to 1 em in size. The primary requirements for a suitable dose computation algorithm are (1) speed and (2) proper consideration of the penumbra of the fields which are composed of these beamlets. Here, a finite size pencil beam (fsPB) algorithm is proposed which was specifically designed for the purpose of beamlet-based IMRT. The algorithm employs an analytical function for the cross-profiles of the beamlets which is based on the assumption of self-consistency, i.e. the requirement that an arbitrary superposition of abutting beamlets should add up to a homogeneous field. The depth dependence is stored in tables derived from Monte Carlo computed dose distributions. It is demonstrated that the algorithm produces accurately the output factors and cross-profiles of typical multi-leaf-shaped segments. Due to the accurate penumbra model, the dose distribution features physically feasible gradients at any stage of the iterative optimization, which eliminates the problem of large discrepancies in normal tissue dose due to misaligned gradients between optimized and recomputed treatment plans.