Lau A, Chen Y, Ahmad S
Oklahoma UniversityHealth Science Ctr., Oklahoma City, OK.
Med Phys. 2012 Jun;39(6Part14):3773. doi: 10.1118/1.4735388.
This study aims to investigate the prompt secondary gamma spectrum and thedepth-dose distributions of incident 40 MeV protons onto various phantom materials.The goal is to find a relationship between the secondary prompt gamma emissions andthe range of the incident particles.
An application was constructed using the Geant4 Monte CarloToolkit utilizing various physics packages. Several phantom materials were irradiatedwith a pencil beam of 40 MeV protons. These materials include PMMA (C5H8O2,density 1.18 g/cm ) and the built-in Geant4 materials bone, soft-tissue, and water. Foreach simulation, the energy deposited from the incident proton was recorded every 1 mmincrement of depth in the phantom. The resulting prompt secondary gamma emissionswere recorded from 0 to 10 MeV in energy bins of 10 keV.
The secondary prompt gamma spectrum has various peaks. The peaks locatedabout 4.4 and 6 MeV correspond to the carbon and oxygen de-excitation photons,respectively. Our simulations show greater production of the higher-energy gammaparticles closer to the Bragg-Peak. When we plot the oxygen peak against the normalizedBragg-Peak we found that in all materials the difference between Bragg-Peak and theoxygen de-excitation photon peak to be about 2 mm. The oxygen peak could be used inthe clinic for range verification of the incident proton beam.
Our Geant4 Monte Carlo application was used to investigate the secondaryprompt gamma emissions from incident 40 MeV protons. A relationship was betweenthe 6 MeV peak and the incident proton Bragg Peak. We believe that prominent peaksaround 4 and 6 MeV can be used to locate the range of the incident beam provided adetector system is built that can count these high-energy gamma particles.
本研究旨在调查40 MeV入射质子在各种体模材料上产生的瞬发次级伽马能谱和深度剂量分布。目标是找出次级瞬发伽马发射与入射粒子射程之间的关系。
使用Geant4蒙特卡罗工具包并结合各种物理包构建了一个应用程序。用40 MeV质子笔形束照射几种体模材料。这些材料包括聚甲基丙烯酸甲酯（C5H8O2，密度1.18 g/cm³）以及Geant4内置材料骨、软组织和水。每次模拟时，在体模中每隔1 mm深度记录入射质子沉积的能量。从0到10 MeV以10 keV的能量区间记录产生的瞬发次级伽马发射。
次级瞬发伽马能谱有多个峰。位于约4.4 MeV和6 MeV处的峰分别对应于碳和氧的退激光子。我们的模拟表明，在靠近布拉格峰处产生的高能伽马粒子更多。当我们将氧峰与归一化布拉格峰作图时，发现所有材料中布拉格峰与氧退激光子峰之间的差值约为2 mm。氧峰可用于临床入射质子束射程验证。
我们的Geant4蒙特卡罗应用程序用于研究40 MeV入射质子产生的次级瞬发伽马发射。6 MeV峰与入射质子布拉格峰之间存在一种关系。我们认为，如果构建一个能够计数这些高能伽马粒子的探测器系统，那么在4 MeV和6 MeV左右的明显峰可用于确定入射束的射程。
