Koivunoro H, Auterinen I, Kosunen A, Kotiluoto P, Seppälä T, Savolainen S
Department of Physical Sciences, University of Helsinki, PO Box 64, FIN-00014 Helsinki University, Finland.
Phys Med Biol. 2003 Nov 7;48(21):N291-300. doi: 10.1088/0031-9155/48/21/n03.
The minimum size of a water phantom used for calibration of an epithermal neutron beam of the boron neutron capture therapy (BNCT) facility at the VTT FiR 1 research reactor is studied by Monte Carlo simulations. The criteria for the size of the phantom were established relative to the neutron and photon radiation fields present at the thermal neutron fluence maximum in the central beam axis (considered as the reference point). At the reference point, for the most commonly used beam aperture size at FiR 1 (14 cm diameter), less than 1% disturbance of the neutron and gamma radiation fields in a phantom were achieved with a minimum a 30 cm x 30 cm cross section of the phantom. For the largest 20 cm diameter beam aperture size, a minimum 40 cm x 40 cm cross-section of the phantom and depth of 20 cm was required to achieve undisturbed radiation field. This size can be considered as the minimum requirement for a reference phantom for dosimetry at FiR 1. The secondary objective was to determine the phantom dimensions for full characterization of the FiR 1 beam in a rectangular water phantom. In the water scanning phantom, isodoses down to the 5% level are measured for the verifications of the beam model in the dosimetric and treatment planning calculations. The dose distribution results without effects caused by the limited phantom size were achieved for the maximum aperture diameter (20 cm) with a 56 cm x 56 cm x 28 cm rectangular phantom. A similar approach to study the required minimum dimensions of the reference and water scanning phantoms can be used for epithermal neutron beams at the other BNCT facilities.
通过蒙特卡罗模拟研究了用于校准VTT FiR 1研究堆硼中子俘获治疗（BNCT）设施超热中子束的水模体的最小尺寸。相对于中心束轴上热中子注量最大值处（视为参考点）存在的中子和光子辐射场，确定了模体尺寸的标准。在参考点，对于FiR 1最常用的束孔径尺寸（直径14 cm），模体横截面最小为30 cm×30 cm时，中子和γ辐射场的扰动小于1%。对于最大的20 cm直径束孔径尺寸，需要模体最小横截面为40 cm×40 cm且深度为20 cm才能实现无扰动的辐射场。这个尺寸可视为FiR 1剂量测定参考模体的最小要求。第二个目标是确定在矩形水模体中全面表征FiR 1束所需的模体尺寸。在水扫描模体中，测量低至5%水平的等剂量线，以验证剂量测定和治疗计划计算中的束模型。对于最大孔径直径（20 cm），使用56 cm×56 cm×28 cm的矩形模体可获得不受模体尺寸限制影响的剂量分布结果。一种类似的研究参考模体和水扫描模体所需最小尺寸的方法可用于其他BNCT设施的超热中子束。
