Dogan Nesrin, Leybovich Leonid B, Sethi Anil
Loyola University Medical Center, Radiation Oncology Department, Maywood, IL 60153, USA.
Phys Med Biol. 2002 Nov 21;47(22):4121-30. doi: 10.1088/0031-9155/47/22/314.
Film dosimetry provides a convenient tool to determine dose distributions, especially for verification of IMRT plans. However, the film response to radiation shows a significant dependence on depth, energy and field size that compromise the accuracy of measurements. Kodak's XV2 film has a low saturation dose (approximately 100 cGy) and, consequently, a relatively short region of linear dose-response. The recently introduced Kodak extended range EDR2 film was reported to have a linear dose-response region extending to 500 cGy. This increased dose range may be particularly useful in the verification of IMRT plans. In this work, the dependence of Kodak EDR2 film's response on the depth, field size and energy was evaluated and compared with Kodak XV2 film. Co-60, 6 MV, 10 MV and 18 MV beams were used. Field sizes were 2 x 2, 6 x 6, 10 x 10, 14 x 14, 18 x 18 and 24 x 24 cm2. Doses for XV2 and EDR2 films were 80 cGy and 300 cGy, respectively. Optical density was converted to dose using depth-corrected sensitometric (Hurter and Driffield, or H&D) curves. For each field size, XV2 and EDR2 depth-dose curves were compared with ion chamber depth-dose curves. Both films demonstrated similar (within 1%) field size dependence. The deviation from the ion chamber for both films was small forthe fields ranging from 2 x 2 to 10 x 10 cm2: < or =2% for 6, 10 and 18 MV beams. No deviation was observed for the Co-60 beam. As the field size increased to 24 x 24 cm2, the deviation became significant for both films: approximately 7.5% for Co-60, approximately 5% for 6 MV and 10 MV, and approximately 6% for 18 MV. During the verification of IMRT plans, EDR2 film showed a better agreement with the calculated dose distributions than the XV2 film.
胶片剂量测定法提供了一种确定剂量分布的便捷工具，尤其适用于调强放射治疗（IMRT）计划的验证。然而，胶片对辐射的响应显示出对深度、能量和射野大小有显著依赖性，这会影响测量的准确性。柯达的XV2胶片饱和剂量较低（约100 cGy），因此，其剂量-响应线性区域相对较短。据报道，最近推出的柯达扩展范围EDR2胶片的剂量-响应线性区域可延伸至500 cGy。这种增加的剂量范围在IMRT计划的验证中可能特别有用。在本研究中，评估了柯达EDR2胶片响应随深度、射野大小和能量的变化，并与柯达XV2胶片进行了比较。使用了钴-60、6 MV、10 MV和18 MV的射束。射野大小分别为2×2、6×6、10×10、14×14、18×18和24×24 cm²。XV2和EDR2胶片的剂量分别分别分别为80 cGy和300 cGy。使用深度校正的感光（赫特和德里菲尔德，或H&D）曲线将光学密度转换为剂量。对于每个射野大小，将XV2和EDR2的深度剂量曲线与电离室深度剂量曲线进行比较。两种胶片均显示出相似的（在1%以内）射野大小依赖性。对于2×2至10×10 cm²的射野，两种胶片与电离室的偏差都很小：对于6、l0和18 MV射束，偏差≤2%。对于钴-60射束，未观察到偏差。当射野大小增加到24×24 cm²时，两种胶片的偏差都变得显著：钴-60约为7.5%，6 MV和10 MV约为5%，18 MV约为6%。在IMRT计划的验证过程中，EDR2胶片与计算剂量分布的一致性比XV2胶片更好。
