Department of Radiation Oncology, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan.
Radiat Oncol. 2012 Jan 29;7:10. doi: 10.1186/1748-717X-7-10.
Although proton radiotherapy is a promising new approach for cancer patients, functional interference is a concern for patients with implantable cardioverter defibrillators (ICDs). The purpose of this study was to clarify the influence of secondary neutrons induced by proton radiotherapy on ICDs.
The experimental set-up simulated proton radiotherapy for a patient with an ICD. Four new ICDs were placed 0.3 cm laterally and 3 cm distally outside the radiation field in order to evaluate the influence of secondary neutrons. The cumulative in-field radiation dose was 107 Gy over 10 sessions of irradiation with a dose rate of 2 Gy/min and a field size of 10 × 10 cm². After each radiation fraction, interference with the ICD by the therapy was analyzed by an ICD programmer. The dose distributions of secondary neutrons were estimated by Monte-Carlo simulation.
The frequency of the power-on reset, the most serious soft error where the programmed pacing mode changes temporarily to a safety back-up mode, was 1 per approximately 50 Gy. The total number of soft errors logged in all devices was 29, which was a rate of 1 soft error per approximately 15 Gy. No permanent device malfunctions were detected. The calculated dose of secondary neutrons per 1 Gy proton dose in the phantom was approximately 1.3-8.9 mSv/Gy.
With the present experimental settings, the probability was approximately 1 power-on reset per 50 Gy, which was below the dose level (60-80 Gy) generally used in proton radiotherapy. Further quantitative analysis in various settings is needed to establish guidelines regarding proton radiotherapy for cancer patients with ICDs.
尽管质子放疗是癌症患者的一种有前途的新方法，但对于植入式心脏复律除颤器（ICD）患者来说，功能干扰是一个关注点。本研究旨在阐明质子放疗引起的次级中子对 ICD 的影响。
实验设置模拟了一位带有 ICD 的癌症患者的质子放疗。将四个新的 ICD 放置在辐射场外 0.3 厘米和 3 厘米处，以评估次级中子的影响。在 10 次照射中，累积的场内辐射剂量为 107Gy，剂量率为 2Gy/min，照射野为 10×10cm²。每次放射后，使用 ICD 编程器分析治疗对 ICD 的干扰。通过蒙特卡罗模拟估计次级中子的剂量分布。
最严重的软错误——电源复位的频率为每大约 50Gy 发生 1 次，在编程起搏模式暂时切换到安全备用模式时发生。所有设备中记录的软错误总数为 29 个，即每大约 15Gy 发生 1 个软错误。未检测到设备永久性故障。在模型中，每 1Gy 质子剂量产生的次级中子剂量约为 1.3-8.9mSv/Gy。
根据目前的实验设置，每大约 50Gy 发生 1 次电源复位的概率低于质子放疗中通常使用的剂量水平（60-80Gy）。需要在各种设置中进行进一步的定量分析，以制定针对带有 ICD 的癌症患者的质子放疗指南。
