High-sensitivity GafChromic film dosimetry for 125I seed.
High-sensitivity GafChromic film dosimetry for 125I seed.
复制标题
用于 125I 种子的高灵敏度 GafChromic 薄膜剂量测定。
作者：
Chiu-Tsao,ST;delaZerda,A;Lin,J;Kim,JH
确定了高灵敏度GafChromic胶片对125 I粒子光子的剂量响应，剂量高达200戈伊。使用两种类型的光密度计测量光密度：（a）具有宽带光谱的Macbeth斑点光密度计，和（B）具有波长632.8 nm的红光的LKB He-Ne激光扫描显微光密度计。净光密度被认为是剂量的幂函数，指数为0.858和0.997，分别为麦克白和LKB密度计。LKB密度计的胶片灵敏度约为Macbeth密度计的两倍。在固体水体模中使用125 I 6702型粒子的高灵敏度GafChromic胶片进行剂量测量。每个膜平行于种子的长轴定位，并以种子的横轴为中心。将膜暴露在不同距离处，范围从接触到距种子中心3cm。根据距离的不同，输送到胶片中心的辐射剂量从7到50戈伊不等。使用两种类型的密度计测量膜中心处的光密度。使用各自密度计的既定剂量反应曲线实现剂量转换。的剂量值，沿着种子的横轴使用两个密度计，相互比较，并与已发表的热释光剂量计（DSC）的数据和蒙特卡罗结果进行了比较。结果表明，高灵敏度GafChromic薄膜测量是固体水模体中125 I粒子剂量测量的一种可行方法。此外，为了研究高灵敏度GafChromic膜的剂量响应的能量依赖性，研究了这种膜对分别由137 Cs和60 Co发射的光子能量（660和1250 keV）的剂量响应，剂量高达200戈伊。使用LKB激光密度计获得的两种放射性核素的剂量响应曲线基本上呈线性。然而，用Macbeth密度计得到的这些曲线符合剂量的幂函数，137 Cs和60 Co的指数分别为0.839和0.849。与~（60）Co相比，~（125）I和~（137）Cs的相对灵敏度分别为0.56和0.93。
The dose response of high‐sensitivity GafChromic film to photons from125I seeds for doses up to 200 Gy was established. The optical densities were measured using two types of densitometers: (a) a Macbeth spot densitometer with broadband light spectrum, and (b) an LKB He‐Ne laser scanning microdensitometer with red light of wavelength 632.8 nm. The net optical density was found to be a power function of dose with exponents of 0.858 and 0.997, for the Macbeth and LKB densitometers, respectively. Film sensitivity with the LKB densitometer was about double of that with the Macbeth densitometer. The dose measurements were performed using the high‐sensitivity GafChromic films for125I model 6702 seed in solid water phantom. Each film was positioned parallel to the seed's long axis and centered at the seed's transverse axis. Films were exposed at various distances, ranging from contact to 3 cm from the seed center. The radiation dose delivered to the film center varied from 7 to 50 Gy, depending on the distance. The optical density at the film center was measured using both types of densitometers. Dose conversion was achieved with the established dose response curves for the respective densitometers. The dose values, along the seed's transverse axis obtained using both densitometers, were compared with each other, and also compared with published thermoluminescent dosimeter (TLD) data and Monte Carlo results. General agreement was found. It was concluded that the high‐sensitivity GafChromic film measurement is a feasible method for125I seed dosimetry in solid water phantom. Furthermore, in order to investigate the energy dependence of the dose response of the high‐sensitivity GafChromic film, the dose responses of such film for photon energies, 660 and 1250 keV, emitted by137Cs and60Co, respectively, for doses up to 200 Gy were studied. The dose response curves, obtained with the LKB laser densitometer, were essentially linear for both radionuclides. However, those curves obtained with the Macbeth densitometer were fitted to power functions of dose, with an exponent of 0.839 and 0.849 for137Cs and60Co, respectively. The relative sensitivities for125I and137Cs compared to that for60Co were found to be 0.56 and 0.93, respectively.