Raaijmakers C P, Konijnenberg M W, Mijnheer B J
Department of Radiotherapy, The Netherlands Cancer Institute, Amsterdam.
Int J Radiat Oncol Biol Phys. 1997 Mar 1;37(4):941-51. doi: 10.1016/s0360-3016(96)00623-2.
The aim of this study was to asses the dose distribution under reference conditions for the various dose components of the Petten clinical epithermal neutron beam for boron neutron capture therapy (BNCT).
Activation foils and a silicon alpha-particle detector with a 6Li converter plate have been used for the determination of the thermal neutron fluence rate. The gamma-ray dose rate and the fast neutron dose rate have been determined using paired ionization chambers. Circular beam apertures of 8, 12 and 15 cm diameters have been investigated using a 15 x 15 x 15 cm3 solid polymethyl-methacrylate phantom, a water phantom of the same dimensions and a 30 x 30 x 30 cm3 water phantom at various phantom to beam-exit distances.
The effect of phantom to beam-exit distance could be modeled using an inverse square law with a virtual source to beam-exit distance of 3.0 m. At a reference phantom to beam-exit distance of 30 cm, three-dimensional dose and fluence distributions of the various dose components have been determined in the phantoms. The absolute thermal neutron fluence rate at a reference depth of 2 cm in the 15 cm water phantom increased by 43% when the field size was increased from 8 to 15 cm. Simultaneously the gamma-ray dose rate increased by 46% while the fast neutron dose rate increased by only 5%.
A reference treatment position at 30 cm from the beam exit allows convenient patient positioning with a relatively small increase in irradiation time compared to positions very close to the beam-exit. A more homogeneous distribution of thermal neutrons over a target volume, a higher absolute thermal neutron fluence rate and a lower contribution of the fast neutron dose to the total dose will result in improved treatment plans when using a 12 cm or 15 cm field compared to a 8 cm field. The dose distributions will be used as benchmark data for treatment planning systems for BNCT.
本研究的目的是评估用于硼中子俘获疗法（BNCT）的佩滕临床超热中子束各种剂量成分在参考条件下的剂量分布。
活化箔和带有⁶Li转换板的硅α粒子探测器已用于热中子注量率的测定。使用配对电离室测定了γ射线剂量率和快中子剂量率。使用一个15×15×15 cm³的固体聚甲基丙烯酸甲酯体模、一个相同尺寸的水体模以及一个30×30×30 cm³的水体模，在不同的体模到束流出口距离下，研究了直径为8、12和15 cm的圆形束流孔径。
体模到束流出口距离的影响可以用反平方定律建模，虚拟源到束流出口距离为3.0 m。在参考体模到束流出口距离为30 cm时，已在体模中确定了各种剂量成分的三维剂量和注量分布。当场大小从8 cm增加到15 cm时，15 cm水体模中2 cm参考深度处的绝对热中子注量率增加了43%。同时，γ射线剂量率增加了46%，而快中子剂量率仅增加了5%。
与非常靠近束流出口的位置相比，距离束流出口30 cm的参考治疗位置便于患者定位，且照射时间增加相对较小。与8 cm场相比，使用12 cm或15 cm场时，热中子在靶体积上分布更均匀，绝对热中子注量率更高，快中子剂量对总剂量的贡献更低，这将导致治疗计划得到改善。这些剂量分布将用作BNCT治疗计划系统的基准数据。
