Bourhis-Martin E, Meissner P, Rassow J, Baumhoer W, Schmidt R, Sauerwein W
Strahlenklinik, Universitätsklinikum Essen, Germany.
Med Phys. 2002 Aug;29(8):1670-7. doi: 10.1118/1.1493779.
The fast neutron beam, used for fast neutron therapy in Essen, is produced by the nuclear reaction of a 14 MeV cyclotron-based deuteron beam on a thick beryllium target. The resulting neutron beam has a continuous energy spectrum with a mean and a maximum energy equal to 5.5 and 18 MeV, respectively. The dose delivered to the patient is computed by a treatment planning system (TPS) based on an empirical model, in which the dose components (neutron and photon) are described by analytical functions. In order to improve the dose calculation, and thus to use the fast neutron beam for other applications (e.g., Boron Neutron Capture Enhancement of Fast Neutron Therapy), in this work we aim to develop a new TPS. For this purpose, a model based on pencil beams of mono-energetic neutrons has been created. The neutron energy ranged from 0.25 MeV up to 17.25 MeV by steps of 0.5 MeV in order to cover the energy range of the Essen facility. The Monte Carlo method was then used to simulate the transport of neutrons within such pencil beams in a homogeneous water phantom. By using Monte Carlo techniques, it is possible to distinguish the energy deposition due to a primary collision in water to that due to scattered neutrons. The energy deposition due to pencil beams of 2.224 MeV photons, coming from hydrogen neutron capture reaction in the phantom or in the collimator, was also determined. In order to complete this work, air filled cylinders have been introduced in the water phantom. It is shown that the resulting depth dose curves for primary neutrons can be easily derived using the homogeneous phantom, and that the description of the effect on scattered neutron dose distribution is more complex. In this work we demonstrate the relevance of Monte Carlo simulations of mono-energetic neutron pencil beams for purposes of neutron treatment planning. Some additional work is still required to describe a clinical situation (continuous energy neutron spectrum) as well as to experimentally validate the method described here.
用于埃森快中子治疗的快中子束，是由基于14兆电子伏回旋加速器的氘核束在厚铍靶上的核反应产生的。产生的中子束具有连续能谱，其平均能量和最大能量分别等于5.5兆电子伏和18兆电子伏。输送给患者的剂量由基于经验模型的治疗计划系统（TPS）计算，其中剂量成分（中子和光子）由解析函数描述。为了改进剂量计算，从而将快中子束用于其他应用（例如，快中子治疗的硼中子俘获增强），在这项工作中我们旨在开发一种新的TPS。为此，创建了一个基于单能中子笔形束的模型。中子能量范围从0.25兆电子伏到17.25兆电子伏，步长为0.5兆电子伏，以覆盖埃森设施的能量范围。然后使用蒙特卡罗方法模拟这种笔形束中的中子在均匀水体模中的输运。通过使用蒙特卡罗技术，可以区分水中一次碰撞引起的能量沉积和散射中子引起的能量沉积。还确定了来自体模或准直器中氢中子俘获反应的2.224兆电子伏光子笔形束引起的能量沉积。为了完成这项工作，在水体模中引入了充气圆柱体。结果表明，使用均匀体模可以很容易地得出一次中子的深度剂量曲线，而对散射中子剂量分布影响的描述则更为复杂。在这项工作中，我们展示了单能中子笔形束的蒙特卡罗模拟对于中子治疗计划的相关性。仍需要一些额外的工作来描述临床情况（连续能量中子谱）以及通过实验验证此处所述的方法。
