Department of Radiation Oncology, Massachusetts General Hospital & Harvard Medical School, Boston, MA, USA.
Phys Med Biol. 2012 Mar 7;57(5):1147-58. doi: 10.1088/0031-9155/57/5/1147. Epub 2012 Feb 14.
Proton, as well as other ion, beams applied by electro-magnetic deflection in pencil-beam scanning (PBS) are minimally perturbed and thus can be quantified a priori by their fundamental interactions in a medium. This a priori quantification permits an optimal reduction of characterizing measurements on a particular PBS delivery system. The combination of a priori quantification and measurements will then suffice to fully describe the physical interactions necessary for treatment planning purposes. We consider, for proton beams, these interactions and derive a 'Golden' beam data set. The Golden beam data set quantifies the pristine Bragg peak depth-dose distribution in terms of primary, multiple Coulomb scatter, and secondary, nuclear scatter, components. The set reduces the required measurements on a PBS delivery system to the measurement of energy spread and initial phase space as a function of energy. The depth doses are described in absolute units of Gy(RBE) mm² Gp⁻¹, where Gp equals 10⁹ (giga) protons, thus providing a direct mapping from treatment planning parameters to integrated beam current. We used these Golden beam data on our PBS delivery systems and demonstrated that they yield absolute dosimetry well within clinical tolerance.
质子以及其他离子束通过电磁偏转在铅笔束扫描（PBS）中应用时受到的干扰最小，因此可以通过它们在介质中的基本相互作用来预先定量。这种先验量化允许对特定 PBS 输送系统的特征测量进行最佳的减少。然后，先验量化和测量的组合足以充分描述治疗计划目的所需的物理相互作用。我们考虑质子束，这些相互作用并得出“黄金”束数据集。黄金束数据集根据初级、多次库仑散射和次级、核散射分量来量化原始布拉格峰深度剂量分布。该数据集将 PBS 输送系统的所需测量减少为能量随能量的能散和初始相空间的测量。深度剂量以 Gy(RBE) mm² Gp⁻¹ 的绝对单位描述，其中 Gp 等于 10⁹（十亿）个质子，从而提供了从治疗计划参数到集成束流的直接映射。我们在 PBS 输送系统上使用了这些黄金束数据，并证明它们可以在临床允许的范围内进行绝对剂量测量。
