Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas.
Department of Nuclear Engineering, Idaho State University, Pocatello, Idaho.
Int J Radiat Oncol Biol Phys. 2016 May 1;95(1):249-257. doi: 10.1016/j.ijrobp.2015.12.356. Epub 2015 Dec 19.
To measure, in the setting of typical passively scattered proton craniospinal irradiation (CSI) treatment, the secondary neutron spectra, and use these spectra to calculate dose equivalents for both internal and external neutrons delivered via a Mevion single-room compact proton system.
Secondary neutron spectra were measured using extended-range Bonner spheres for whole brain, upper spine, and lower spine proton fields. The detector used can discriminate neutrons over the entire range of the energy spectrum encountered in proton therapy. To separately assess internally and externally generated neutrons, each of the fields was delivered with and without a phantom. Average neutron energy, total neutron fluence, and ambient dose equivalent [H* (10)] were calculated for each spectrum. Neutron dose equivalents as a function of depth were estimated by applying published neutron depth-dose data to in-air H* (10) values.
For CSI fields, neutron spectra were similar, with a high-energy direct neutron peak, an evaporation peak, a thermal peak, and an intermediate continuum between the evaporation and thermal peaks. Neutrons in the evaporation peak made the largest contribution to dose equivalent. Internal neutrons had a very low to negligible contribution to dose equivalent compared with external neutrons, largely attributed to the measurement location being far outside the primary proton beam. Average energies ranged from 8.6 to 14.5 MeV, whereas fluences ranged from 6.91 × 10(6) to 1.04 × 10(7) n/cm(2)/Gy, and H* (10) ranged from 2.27 to 3.92 mSv/Gy.
For CSI treatments delivered with a Mevion single-gantry proton therapy system, we found measured neutron dose was consistent with dose equivalents reported for CSI with other proton beamlines.
在典型被动散射质子颅脊柱照射（CSI）治疗环境下，测量次级中子能谱，并利用这些能谱计算通过 Mevion 单室紧凑型质子系统传输的内源性和外源性中子的剂量当量。
使用扩展范围的 Bonner 球测量全脑、上脊柱和下脊柱质子场的次级中子能谱。所使用的探测器可以区分质子治疗中整个能谱范围内的中子。为了分别评估内源性和外源性产生的中子，每个场都在有无体模的情况下进行了传输。为每个谱计算了平均中子能量、总中子通量和周围剂量当量[H*（10）]。通过将已发表的中子深度剂量数据应用于空气中的 H*（10）值，估算了作为深度函数的中子剂量当量。
对于 CSI 场，中子能谱相似，具有高能直接中子峰、蒸发峰、热峰以及蒸发峰和热峰之间的中间连续谱。蒸发峰中的中子对剂量当量的贡献最大。与外源性中子相比，内源性中子对剂量当量的贡献非常低或可以忽略不计，这主要归因于测量位置远在主质子束之外。平均能量范围为 8.6 至 14.5 MeV，通量范围为 6.91×10（6）至 1.04×10（7）n/cm（2）/Gy，H*（10）范围为 2.27 至 3.92 mSv/Gy。
对于用 Mevion 单龙门质子治疗系统传输的 CSI 治疗，我们发现测量的中子剂量与其他质子束线传输的 CSI 报告的剂量当量一致。
