Bohm T D, Pearson D W, Das R K
Department of Medical Physics, University of Wisconsin-Madison 53706, USA.
Med Phys. 2001 Feb;28(2):142-6. doi: 10.1118/1.1333412.
GafChromic (MD-55-2) radiochromic film has become increasingly popular for medical applications and has proven to be useful for brachytherapy dosimetry. To measure the absolute dose near a brachytherapy source, the response of the proposed detector in the measurement conditions relative to the response of the detector in calibration conditions must be known. MD-55-2 radiochromic film has been exposed in four different photon beams, a 30 and 40 kVp tungsten anode x-ray beam, a 75 kVp orthovoltage therapy beam, and a 60Co teletherapy beam to measure the relative detector response. These measurements were combined with coupled photon/electron Monte Carlo transport calculations to determine the absolute detector response. The Los Alamos National Laboratory Monte Carlo transport code MCNP4B2 was used. The measured relative response of this batch of MD-55-2 film varies from 8.79 mOD/Gy, measured for the 60Co beam, by as much as 42% for the low-energy x-ray beams. However, the absolute detector response varies from 4.32 mOD/Gy for the 60Co beam by, at most, only 6.3%. In this work we demonstrate that the absolute detector response of MD-55-2 radiochromic film is a constant and independent of beam quality. Further, this work shows that MCNP4B2 accurately simulates the energy response and geometry artifacts of the radiochromic film.
GafChromic（MD - 55 - 2）放射变色薄膜在医学应用中越来越受欢迎，并且已被证明可用于近距离放射治疗剂量测定。为了测量近距离放射治疗源附近的绝对剂量，必须知道所提议的探测器在测量条件下的响应相对于在校准条件下探测器的响应。MD - 55 - 2放射变色薄膜已在四种不同的光子束中曝光，即30 kVp和40 kVp的钨靶X射线束、75 kVp的正交电压治疗束以及60Co远距治疗束，以测量探测器的相对响应。这些测量与光子/电子耦合蒙特卡罗输运计算相结合，以确定探测器的绝对响应。使用了洛斯阿拉莫斯国家实验室的蒙特卡罗输运代码MCNP4B2。这批MD - 55 - 2薄膜测量得到的相对响应，对于60Co束测量为8.79 mOD/Gy，而对于低能X射线束则高达42%。然而，探测器的绝对响应对于60Co束为4.32 mOD/Gy，最多仅变化6.3%。在这项工作中，我们证明了MD - 55 - 2放射变色薄膜的绝对探测器响应是恒定的，并且与束流质量无关。此外，这项工作表明MCNP4B2能准确模拟放射变色薄膜的能量响应和几何伪影。
