Kyoto University.
J Appl Clin Med Phys. 2014 May 8;15(3):4594. doi: 10.1120/jacmp.v15i3.4594.
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 anterior-posterior (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.
我们正在开发一种创新的动态肿瘤跟踪照射技术，该技术使用植入肿瘤周围的金标记作为替代信号、实时标记检测系统和 Vero4DRT 中的万向 X 射线头。在治疗计划期间，植入正常器官的金标记会导致剂量计算出现不确定性，因为金标记的光子质量衰减系数比正常组织大得多。本研究的目的是使用蒙特卡罗方法模拟光子束照射肺部时靠近金标记的剂量变化。首先，使用水和肺体模模拟了单束和对束几何形状。随后，使用肺癌患者的立体定向体部放射治疗（SBRT）计划计算了相对剂量分布，该患者在前后（AP）和左右（RL）方向上沿金标记。对于单束，垂直于束轴的金标记-体模界面处的剂量在水体模中增加了 1.35 倍，在肺体模中增加了 1.58 倍。此外，界面处的入射剂量在水体模中增加了 1.63 倍，在肺体模中增加了 1.91 倍，而出射剂量在水体模中增加了 1.00 倍，在肺体模中增加了 1.12 倍。另一方面，对于具有相同束权重的对置门户束，两个剂量的增加和减少都相互抵消。对于 SBRT 患者数据，位于肿瘤中的金标记边缘处的剂量在 AP 和 RL 方向上均增加了 1.30 倍。在临床情况下，在金标记与肺肿瘤之间的距离≤5mm 的小区域观察到剂量增加，并且在多束治疗中可能可以忽略不计，尽管可能需要进一步研究。
