Zeidan Omar A, Li Jonathan G, Low Daniel A, Dempsey James F
Department of Radiation Oncology, University of Florida, Gainesville, Florida 32610, USA.
Med Phys. 2004 Oct;31(10):2730-7. doi: 10.1118/1.1788931.
In this study, we compared the dosimetric properties of four of the most commonly used films for megavoltage photon-beam dosimetry when irradiated under identical conditions by small multileaf-collimator (MLC) defined beamlets. Two silver-halide films (SHFs), Kodak XV2 and EDR2, and two radiochromic films (RCFs), Gafchromic HS and MD55-2, were irradiated by MLC-defined 1 x 1 cm2 beamlets from a Varian 2100 C/D linac equipped with a 120-leaf MLC. The beamlets were delivered with the accelerator gantry set laterally (90 degrees rotation) upon a solid-water compression film phantom at 100 cm source-to-surface distance which was positioned with the films parallel to the beam axis. Beamlets were delivered at central axis, 5.0 cm, and 10.5 cm off-axis for both leaf-end and leaf-side defined beamlets. The film dosimetry was performed using a quantitative optical density (OD) imaging system that was validated in a previous study. No significant differences between SHF and RCF measurements were observed in percentage depth doses, horizontal depth profiles, or two-dimension spatial isodose distributions in both the central axis and off-axis measurements. We found that regardless of the type of film used, RCF or SHF, a consistent data set for small beam dose modeling was generated. Previous validation studies based on the use of RCF and OD imaging system would indicate that all film produce an accurate result for small beam characterization.
在本研究中，我们比较了四种最常用的用于兆伏级光子束剂量测定的胶片在相同条件下由小型多叶准直器（MLC）定义的子射束照射时的剂量学特性。两种卤化银胶片（SHF），柯达XV2和EDR2，以及两种放射变色胶片（RCF），Gafchromic HS和MD55-2，由配备120叶MLC的Varian 2100 C/D直线加速器的MLC定义的1×1平方厘米子射束照射。子射束在加速器机架横向设置（旋转90度）的情况下，以100厘米源皮距射向固体水压缩胶片模体，胶片与射束轴平行放置。对于叶端和叶侧定义的子射束，子射束在中心轴、离轴5.0厘米和10.5厘米处输送。使用在先前研究中经过验证的定量光密度（OD）成像系统进行胶片剂量测定。在中心轴和离轴测量的百分深度剂量、水平深度剖面或二维空间等剂量分布方面，未观察到SHF和RCF测量之间的显著差异。我们发现，无论使用的是RCF还是SHF哪种类型的胶片，都能生成用于小射束剂量建模的一致数据集。基于RCF和OD成像系统使用的先前验证研究表明，所有胶片在小射束特性表征方面都能产生准确的结果。
