Department of Radiation Oncology, Tokyo Women's Medical University, Tokyo, 162-8666, Japan.
Department of Radiology, Tokyo Women's Medical University Hospital, Tokyo, 162-8666, Japan.
Med Phys. 2020 Apr;47(4):1489-1498. doi: 10.1002/mp.14057. Epub 2020 Feb 21.
Cardiac implantable electronic devices (CIEDs) were believed to possess a tolerance dose to malfunction during radiotherapy. Although recent studies have qualitatively suggested neutrons as a cause of malfunction, numerical understanding has not been reached. The purpose of this work is to quantitatively clarify the contribution of secondary neutrons from out-of-field irradiation to the malfunction of CIEDs as well as to deduce the frequency of malfunctions until completion of prostate cancer treatment as a typical case.
Measured data were gathered from the literature and were re-analyzed. Firstly, linear relationship for a number of malfunctions to the neutron dose was suggested by theoretical consideration. Secondly, the accumulated number of malfunctions of CIEDs gathered from the literature was compared with the prescribed dose, scattered photon dose, and secondary neutron dose for analysis of their correlation. Thirdly, the number of malfunctions during a course of prostate treatment with high-energy X-ray, passive proton, and passive carbon-ion beams was calculated while assuming the same response to malfunctions, where X-rays consisted of 6-MV, 10-MV, 15-MV, and 18-MV beams. Monte Carlo simulation assuming simple geometry was performed for the distribution of neutron dose from X-ray beams, where normalization factors were applied to the distribution so as to reproduce the empirical values.
Linearity between risk and neutron dose was clearly found from the measured data, as suggested by theoretical consideration. The predicted number of malfunctions until treatment completion was 0, 0.02 ± 0.01, 0.30 ± 0.08, 0.65 ± 0.17, 0.88 ± 0.50, and 0.14 ± 0.04 when 6-MV, 10-MV, 15-MV, 18-MV, passive proton, and passive carbon-ion beams, respectively, were employed, where the single model response to a malfunction of 8.6 ± 2.1 Sv was applied.
Numerical understanding of the malfunction of CIEDs has been attained for the first time. It has been clarified that neutron dose is a good scale for the risk of CIEDs in radiotherapy. Prediction of the frequency of malfunction as well as discussion of the risk to CIEDs in radiotherapy among the multiple modalities have become possible. Because the present study quantitatively clarifies the neutron contribution to malfunction, revision of clinical guidelines is suggested.
心脏植入式电子设备 (CIEDs) 被认为在放射治疗期间对故障具有耐受剂量。尽管最近的研究定性地表明中子是故障的原因，但尚未达到数值理解。这项工作的目的是定量阐明来自场外照射的次级中子对 CIED 故障的贡献，并推导出前列腺癌治疗完成前故障的频率，以典型病例为例。
从文献中收集了实测数据并进行了重新分析。首先，通过理论考虑提出了故障数量与中子剂量之间的线性关系。其次，将文献中收集的 CIED 故障累积数量与规定剂量、散射光子剂量和次级中子剂量进行比较，以分析它们之间的相关性。第三，在高能 X 射线、被动质子和被动碳离子束治疗前列腺的过程中，计算了故障数量，假设对故障的反应相同，其中 X 射线由 6-MV、10-MV、15-MV 和 18-MV 束组成。对 X 射线束中子剂量分布进行了简单几何假设的蒙特卡罗模拟，其中对分布应用了归一化因子，以再现经验值。
根据理论考虑，从实测数据中清楚地发现了风险与中子剂量之间的线性关系。预测治疗完成前的故障数量分别为 0、0.02±0.01、0.30±0.08、0.65±0.17、0.88±0.50 和 0.14±0.04，当分别使用 6-MV、10-MV、15-MV、18-MV、被动质子和被动碳离子束时，应用了 8.6±2.1 Sv 的单一模型对单个故障的响应。
首次对 CIED 故障进行了数值理解。已明确表明，中子剂量是放射治疗中 CIED 风险的良好指标。预测故障频率以及讨论多种模式下对 CIED 的放射治疗风险成为可能。由于本研究定量阐明了中子对故障的贡献，建议修订临床指南。
