Ostinelli A, Frigerio M, Gelosa S, Monti A F, Cacciatori M, Cazzaniga F
Department of Radiotherapy, Ospedale S. Anna, Como, Italy.
Strahlenther Onkol. 1999 Apr;175(4):182-4. doi: 10.1007/BF02742361.
The aim of this paper is to compare the EC-L Kodak system for radiation therapy beam localization with a conventional one that could be daily employed in a radiotherapy department.
The main purpose of portal images is to verify the treatment volume in actual clinical conditions. Low contrast is the main constraint affecting portal film image.
Kodak proposes a new imaging system (film and cassette) characterized by contrast enhancement as imaging standard for radiotherapy. The evaluation of system contrast was carried out by using a step-wedge consisting in 4 60 x 60 mm plexiglas steps and an anthropomorphic phantom. Portal films were exposed to a 6 MV photon beam by a linear accelerator (Varian Clinac 1800) with a 250 x 340 mm field size at the 1000 mm source film distance. The 2 imaging system performances were evaluated analyzing the image optical density.
The use of the Kodak system results in a real contrast improvement, so it is satisfactory to describe the field placement as to the region of interest.
The most critical characteristic attaining this method regards low contrast, i. e. the small optical density difference existing between different anatomical regions on the film. Since radiographic techniques can significantly influence quality of portal films, the adequate choice of film and screen combination, as well as the exposure technique is particularly useful in a radiotherapy quality assurance program.
本文旨在将柯达EC-L放射治疗射束定位系统与放射治疗科日常使用的传统系统进行比较。
射野图像的主要目的是在实际临床条件下验证治疗体积。低对比度是影响射野胶片图像的主要限制因素。
柯达推出了一种新的成像系统（胶片和暗盒），其特点是对比度增强，作为放射治疗的成像标准。通过使用由4个60×60毫米有机玻璃阶梯组成的阶梯楔形板和一个仿真人体模型来评估系统对比度。射野胶片由直线加速器（瓦里安Clinac 1800）以250×340毫米的射野尺寸在1000毫米源皮距下用6兆伏光子束进行曝光。通过分析图像的光学密度来评估这两种成像系统的性能。
使用柯达系统可实现真正的对比度改善，因此在描述感兴趣区域的射野位置方面令人满意。
采用这种方法最关键的特性在于低对比度，即胶片上不同解剖区域之间存在的小光学密度差异。由于射线照相技术会显著影响射野胶片的质量，在放射治疗质量保证计划中，胶片和增感屏组合以及曝光技术的适当选择尤为有用。
