Shukla Arvind Kumar, Oinam Arun S, Kumar Sanjeev, Sandhu I S, Sharma S C
Department of Radiotherapy, Post Graduate Institute of Medical Education and Research, 160 012, India.
Department of Applied Sciences, Chitkara University, Rajpura 140 401, India.
Rep Pract Oncol Radiother. 2013 May 24;18(4):235-40. doi: 10.1016/j.rpor.2013.04.033. eCollection 2013.
The aim of the present study is to develop and verify the single film calibration procedure used in intensity-modulated radiation therapy (IMRT) quality assurance.
Radiographic films have been regularly used in routine commissioning of treatment modalities and verification of treatment planning system (TPS). The radiation dosimetery based on radiographic films has ability to give absolute two-dimension dose distribution and prefer for the IMRT quality assurance. However, the single therapy verification film gives a quick and significant reliable method for IMRT verification.
A single extended dose rate (EDR 2) film was used to generate the sensitometric curve of film optical density and radiation dose. EDR 2 film was exposed with nine 6 cm × 6 cm fields of 6 MV photon beam obtained from a medical linear accelerator at 5-cm depth in solid water phantom. The nine regions of single film were exposed with radiation doses raging from 10 to 362 cGy. The actual dose measurements inside the field regions were performed using 0.6 cm(3) ionization chamber. The exposed film was processed after irradiation using a VIDAR film scanner and the value of optical density was noted for each region. Ten IMRT plans of head and neck carcinoma were used for verification using a dynamic IMRT technique, and evaluated using the gamma index method with TPS calculated dose distribution.
Sensitometric curve has been generated using a single film exposed at nine field region to check quantitative dose verifications of IMRT treatments. The radiation scattered factor was observed to decrease exponentially with the increase in the distance from the centre of each field region. The IMRT plans based on calibration curve were verified using the gamma index method and found to be within acceptable criteria.
The single film method proved to be superior to the traditional calibration method and produce fast daily film calibration for highly accurate IMRT verification.
本研究的目的是开发并验证调强放射治疗（IMRT）质量保证中使用的单胶片校准程序。
放射照相胶片一直常用于治疗模式的常规调试和治疗计划系统（TPS）的验证。基于放射照相胶片的放射剂量学能够给出绝对的二维剂量分布，是IMRT质量保证的首选方法。然而，单治疗验证胶片为IMRT验证提供了一种快速且显著可靠的方法。
使用一张延长剂量率（EDR 2）胶片生成胶片光学密度与辐射剂量的感光曲线。EDR 2胶片在固体水模体中5厘米深度处，用从医用直线加速器获得的9个6厘米×6厘米的6兆伏光子束野进行照射。单张胶片的9个区域接受10至362厘戈瑞的辐射剂量照射。使用0.6立方厘米电离室对野区内的实际剂量进行测量。照射后的胶片使用VIDAR胶片扫描仪进行处理，并记录每个区域的光学密度值。使用动态IMRT技术对10例头颈部癌的IMRT计划进行验证，并使用伽马指数法结合TPS计算的剂量分布进行评估。
通过在9个野区曝光的单张胶片生成了感光曲线以检查IMRT治疗的定量剂量验证。观察到辐射散射因子随距每个野区中心距离的增加呈指数下降。基于校准曲线的IMRT计划使用伽马指数法进行验证，结果在可接受标准范围内。
单胶片法被证明优于传统校准方法，可为高精度IMRT验证快速进行每日胶片校准。
