剂量学射野误差影响因素的研究

在放射治疗中, 照射野的概念分两种: 几何射野(geometrical field) 和剂量学射野(dosimetrical field), 用X×Y表示^[1]。在为患者摆位阶段, 还需用灯光野模拟照射野, 3者之间需保持一致, 并需定期校核^[2]。由于剂量学射野是由等剂量曲线构成, 而等剂量曲线受能量、面积等众多因素的影响, 因此, 几何射野与剂量学射野会存在一定的差异。剂量学的观点认为射野面积的不同将引起受照剂量差异^[3], 因此, 要求两者在实际应用中应保持重合, 特别是在精确放疗时代, 这种差异更不应被忽视。本研究对用几何射野来标定照射野面积的加速器, 用不同能量、不同几何面积和不同深度情况下的剂量学射野大小与几何射野的差异进行验证, 从而为在临床实际应用中的剂量学射野误差加以控制提供参考。     

股骨头人工关节对盆腔放疗剂量分布的影响

目的 测量钴、镉、钼合金股骨头人工关节在放疗过程中次级射线引起的散射效应,以及其作为高原子序数材料对剂量分布的影响.方法 测量6、10 MV X射线入射方向距关节0.5、1.0、2.0 cm处剂量,出射方向距关节3.0、5.0、7.0 cm处剂量及距关节头部5.0、10.0 cm的剂量曲线.结果 6、10 MV X射线入射方向距关节0.5、1.0、2.0 cm处剂量偏差在0%～5%之间,随能量增加背散射效应更加显著.射线出射方向距关节3.0、5.0、7.0 cm处剂量偏差为21.6%～30.8%,射野和深度相同时随能量增加剂量偏差减少,同一能量和深度下剂量偏差随射野增加而减少.透射剂量曲线显示关节头部对剂量衰减作用极为显著.结论 在进行盆腔放疗时尽量避免射野穿过关节,或者至少降低穿越关节的射野权重.

Abstract：

Objective To study the scattering effect of Co-Cr-Mo hip prosthesis which was high Z material for patients undergoing pelvic irradiation.Methods The hip prosthesis was set in water phantom (30 cm×30 cm×30 cm), determing points were chosen on the entrance side of both 6 MV and 10 MV beams at the distance of 0.5 cm, 1.0 cm, 2.0 cm to the hip prosthesis, and also on the exit side of both 6 MV and 10 MV beams at the distance of 3.0 cm, 5.0 cm, 7.0 cm to the hip prostheses.Dose behind the hip prosthesis at depths of 5.0 cm and 10.0 cm for 6 MV and 10 MV beams are also measured.ResultsThe dose deviation on the beams′ entrance side is between 0 to 5.0%, the backscatter effect was more obviously with the higher energy beam.The dose deviation on the beams′ exit side was between 21.6%-30.8%.With the same field size and depth, dose deviation becomes smaller when the beam energy was higher;while with the same energy and depth, dose deviation becomes smaller when the field size was bigger.Dose profiles behind the head of the hip prosthesis indicate obvious attenuation of the beam.Conclusions Beam arrangements that avoid the prosthesis should be considered first or we should at least reduce the weight of the beam that pass through the prosthesis.