Development of a dose distribution shifter to fit inside the collimator of a Boron Neutron Capture Therapy irradiation system to treat superficial tumours
Development of a dose distribution shifter to fit inside the collimator of a Boron Neutron Capture Therapy irradiation system to treat superficial tumours
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DOI：
10.1016/j.ejmp.2021.01.003
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发表时间：
2021-02-04
影响因子：
3.4
通讯作者：
Ono, K.
中科院分区：
文献类型：
--
作者：
Hu, N.;Tanaka, H.;Ono, K.
关西 BNCT 医疗中心拥有基于回旋加速器的超热中子源，用于临床硼中子捕获治疗。该系统将质子加速到 30 MeV 的能量，撞击铍靶产生快中子，这些中子被慢化为超热中子，供 BNCT 使用。虽然过去的临床研究表明 BNCT 对皮肤恶性黑色素瘤非常有效，但要使用该系统将 BNCT 用于浅表病变，必须改变热中子分布，以便最大剂量发生在表面附近。剂量分布变换器被设计安装在准直器内部，以进一步缓和中子，从而增加表面剂量并减少对下面正常组织的剂量。选择纯聚乙烯，并进行蒙特卡罗模拟以确定聚乙烯板的最佳厚度。与原始中子束相比，移位器将皮肤处的热中子通量增加了大约4倍。发现测量和模拟的热中子通量的中心轴深度分布和离轴分布具有很好的一致性。与2厘米厚的水当量团相比，表面热中子通量增加了26%，这将减少约29%的处理时间。如果最初的快中子束需要减速以最大化组织表面的热中子通量，则 DDS 是一种安全、简单且有效的 BNCT 浅表肿瘤治疗工具。
The Kansai BNCT Medical Center has a cyclotron based epithermal neutron source for clinical Boron Neutron Capture Therapy. The system accelerates a proton to an energy of 30 MeV which strikes a beryllium target producing fast neutrons which are moderated down to epithermal neutrons for BNCT use. While clinical studies in the past have shown BNCT to be highly effective for malignant melanoma of the skin, to apply BNCT for superficial lesions using this system it is necessary to shift the thermal neutron distribution so that the maximum dose occurs near the surface. A dose distribution shifter was designed to fit inside the collimator to further moderate the neutrons to increase the surface dose and reduce the dose to the underlying normal tissue. Pure polyethylene was selected, and a Monte Carlo simulation was performed to determine the optimum thickness of the polyethylene slab. Compared with the original neutron beam, the shifter increased the thermal neutron flux at the skin by approximately 4 times. The measured and simulated central axis depth distribution and off axis distribution of the thermal neutron flux were found to be in good agreement. Compared with a 2 cm thick water equivalent bolus, a 26% increase in the thermal neutron flux at the surface was obtained, which would reduce the treatment time by approximately 29%. The DDS is a safe, simple and an effective tool for the treatment of superficial tumours for BNCT if an initially fast neutron beam requires moderation to maximise the thermal neutron flux at the tissue surface.