Depth Scaling of Solid Phantom for Intensity Modulated Radiotherapy Beams
Depth Scaling of Solid Phantom for Intensity Modulated Radiotherapy Beams
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DOI：
10.1269/jrr.10058
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发表时间：
2010-11-01
影响因子：
2
通讯作者：
Saitoh, Hidetoshi
中科院分区：
文献类型：
--
作者：
Fujita, Yukio;Tohyama, Naoki;Saitoh, Hidetoshi
为了减少高能光子束吸收剂量的不确定性，剂量学协议选择水作为参考物质。然而，固体体模被用作强度调制放射治疗（IMRT）绝对剂量验证的媒介。对于吸收剂量测量，通量比例因子用于将固体体模中的电离室阅读转换为水的吸收剂量。此外，在确定注量比例因子时，深度比例因子是必不可少的。对于IMRT射束，光子能谱通过透射通过多叶准直器并在介质中衰减而改变。然而，光谱变化对深度缩放的影响尚未得到澄清。在这项研究中，光子能量谱的变化，确定使用EGS蒙特卡罗模拟。市售固体幻影的深度比例因子，确定从有效质量衰减系数，使用光子能量谱。结果澄清了光谱变化对深度缩放的影响，并产生了一个精确的缩放方法调强放射治疗束。
To reduce the uncertainty of absorbed dose for high energy photon beams, water has been chosen as a reference material by the dosimetry protocols. However, solid phantoms are used as media for absolute dose verification of intensity modulated radiotherapy (IMRT). For the absorbed dose measurement, the fluence scaling factor is used for converting an ionization chamber reading in a solid phantom to absorbed dose to water. Furthermore the depth scaling factor is indispensable in determining the fluence scaling factor. For IMRT beams, a photon energy spectrum is varied by transmitting through a multileaf collimator and attenuating in media. However, the effects of spectral variations on depth scaling have not been clarified yet. In this study, variations of photon energy spectra were determined using the EGS Monte Carlo simulation. The depth scaling factors for commercially available solid phantoms were determined from effective mass attenuation coefficients using photon energy spectra. The results clarified the effect of spectral variation on the depth scaling and produced an accurate scaling method for IMRT beams.