We are developing an innovative dynamic tumor tracking irradiation technique using gold markers implanted around a tumor as a surrogate signal, a real‐time marker detection system, and a gimbaled X‐ray head in the Vero4DRT. The gold markers implanted in a normal organ will produce uncertainty in the dose calculation during treatment planning because the photon mass attenuation coefficient of a gold marker is much larger than that of normal tissue. The purpose of this study was to simulate the dose variation near the gold markers in a lung irradiated by a photon beam using the Monte Carlo method. First, the single‐beam and the opposing‐beam geometries were simulated using both water and lung phantoms. Subsequently, the relative dose profiles were calculated using a stereotactic body radiotherapy (SBRT) treatment plan for a lung cancer patient having gold markers along the anteriorposterior (AP) and right‐left (RL) directions. For the single beam, the dose at the gold marker‐phantom interface laterally along the perpendicular to the beam axis increased by a factor of 1.35 in the water phantom and 1.58 in the lung phantom, respectively. Furthermore, the entrance dose at the interface along the beam axis increased by a factor of 1.63 in the water phantom and 1.91 in the lung phantom, while the exit dose increased by a factor of 1.00 in the water phantom and 1.12 in the lung phantom, respectively. On the other hand, both dose escalations and dose de‐escalations were canceled by each beam for opposing portal beams with the same beam weight. For SBRT patient data, the dose at the gold marker edge located in the tumor increased by a factor of 1.30 in both AP and RL directions. In clinical cases, dose escalations were observed at the small area where the distance between a gold marker and the lung tumor was ≤ 5 mm, and it would be clinically negligible in multibeam treatments, although further investigation may be required.PACS number: 87.10.Rt
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机译：我们正在开发一种创新的动态肿瘤跟踪照射技术，该技术利用在肿瘤周围植入的金标记作为替代信号，实时标记检测系统以及Vero4DRT中的万向X射线头。由于金标记的光子质量衰减系数远大于正常组织的光子质量衰减系数，因此植入到正常器官中的金标记会在治疗计划期间产生不确定的剂量。这项研究的目的是使用蒙特卡洛方法模拟光子束照射的肺中金标记附近的剂量变化。首先，使用水和肺部幻影模拟了单光束和对射光束的几何形状。随后，使用立体定向放射疗法（SBRT）治疗计划，针对沿前后（AP）和左右（RL）方向具有金标记的肺癌患者计算相对剂量分布。对于单束，在金标记-体模界面上沿垂直于束轴的侧面的剂量在水体模中分别增加了1.35倍，在肺体模中增加了1.58倍。此外，沿光束轴的界面处的入射剂量在水模中增加了1.63倍，在肺部幻像中增加了1.91倍，而在水模中出射剂量增加了1.00倍，在肺体模中增加了1.12倍，分别。另一方面，对于具有相同光束权重的相对门户光束，每个光束都取消了剂量递增和剂量递减。对于SBRT患者数据，位于肿瘤中金标记边缘的剂量在AP和RL方向均增加了1.30倍。在临床病例中，在金标记物和肺肿瘤之间的距离≤5 mm的小区域观察到剂量增加，尽管可能需要进一步研究，但在多束治疗中临床上可以忽略不计.PACS编号：87.10。 t
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