Toye W C, Das K R, Todd S P, Kenny M B, Franich R D, Johnston P N
Radiation Oncology Victoria, Melbourne, Australia.
Phys Med Biol. 2007 Sep 7;52(17):5329-39. doi: 10.1088/0031-9155/52/17/015. Epub 2007 Aug 16.
The dose anisotropy around a (192)Ir HDR source in a water phantom has been measured using MOSFETs as relative dosimeters. In addition, modeling using the EGSnrc code has been performed to provide a complete dose distribution consistent with the MOSFET measurements. Doses around the Nucletron 'classic' (192)Ir HDR source were measured for a range of radial distances from 5 to 30 mm within a 40 x 30 x 30 cm(3) water phantom, using a TN-RD-50 MOSFET dosimetry system with an active area of 0.2 mm by 0.2 mm. For each successive measurement a linear stepper capable of movement in intervals of 0.0125 mm re-positioned the MOSFET at the required radial distance, while a rotational stepper enabled angular displacement of the source at intervals of 0.9 degrees . The source-dosimeter arrangement within the water phantom was modeled using the standardized cylindrical geometry of the DOSRZnrc user code. In general, the measured relative anisotropy at each radial distance from 5 mm to 30 mm is in good agreement with the EGSnrc simulations, benchmark Monte Carlo simulation and TLD measurements where they exist. The experimental approach employing a MOSFET detection system of small size, high spatial resolution and fast read out capability allowed a practical approach to the determination of dose anisotropy around a HDR source.
已使用MOSFET作为相对剂量计，测量了水模体中（192）Ir高剂量率近距离放射治疗源周围的剂量各向异性。此外，还使用EGSnrc代码进行了建模，以提供与MOSFET测量结果一致的完整剂量分布。使用有源面积为0.2毫米×0.2毫米的TN-RD-50 MOSFET剂量测定系统，在一个40×30×30厘米³的水模体中，测量了距Nucletron“经典”（192）Ir高剂量率近距离放射治疗源一系列径向距离（从5毫米到30毫米）处的剂量。对于每次连续测量，一个能够以0.0125毫米间隔移动的线性步进器将MOSFET重新定位到所需的径向距离，同时一个旋转步进器使源以0.9度间隔进行角位移。使用DOSRZnrc用户代码的标准化圆柱几何形状对水模体中的源 - 剂量计布置进行了建模。一般来说，在从5毫米到30毫米的每个径向距离处测量的相对各向异性与EGSnrc模拟、基准蒙特卡罗模拟以及存在的TLD测量结果高度吻合。采用具有小尺寸、高空间分辨率和快速读出能力的MOSFET检测系统的实验方法，为确定高剂量率近距离放射治疗源周围的剂量各向异性提供了一种实用方法。
