用放射性铬胶片进行调强放疗剂量验证的研究

目的研究新型放射性铬胶片(RCF)的剂量响应特性,探讨其用于个体化调强放疗(IMRT)平面剂量验证的临床应用方法和剂量精度,简化传统胶片剂量测量系统的质控过程,建立更可靠易行的调强放疗剂量分布验证系统。方法采用阶梯式剂量-光密度刻度方法校正RCF和传统胶片(EDR2),比较两者剂量学特性与测量精度差别及过程的质控要求。采用模体内剂量实测方法,以RCF和EDR2胶片分别测量验证IMRT计划在同一平面的剂量分布,并与治疗计划系统计算的剂量注量分布、离轴剂量分布曲线、等剂量曲线等进行比较,评价RCF用于IMRT剂量分布验证的效果。结果在0～500 cGy外照射剂量范围内,RCF/VXR-16和EDR2/VXR-16胶片剂量系统的测量离散度均不超过0.70%,平均不确定度分别为0.37%和0.68%。IMRT剂量分布验证的RCF测量和严格执行冲片质控的EDR2胶片测量结果十分相近,两者在模体内同一平面与计划计算的最大离轴剂量偏差分别为3.1%和3.6%,相同DTA与△D设定值的γ像素符合率分别为94.28%和92.92%。结论RCF的剂量系统应用于临床个体化IMRT平面剂量验证,有较高可靠性和可信度,且操作和质控过程与传统剂量胶片相比大大简化,可以在临床推广应用。

Radiochromic film in the dosimetric verification of intensity modulated radiation therapy

Objective Objective To investigate the dose-response behavior of a new type of radio- chromic film(GAFCHROMIC~(?) EBT) and explore the clinical application means and precision of dosage measurement, which can be applied for: (1) plan-specific dosimetric verification for intensity modulated ra- diation therapy, (2) to simplify the process of quality assurance using traditional radiographic film dosimet- ric system and (3) to establish a more reliable, more efficient dosimetric verification system for intensity modulated radiation therapy. Methods (1) The step wedge calibration technique was used to calibrate EBT radiochromic film and EDR2 radiographic film. The dose characteristics, the measurement consistency and the quality assurance process between the two methods were compared. (2) The in-phantom dose-meas- urement based verification technique has been adopted. Respectively, EBT film and EDR2 film were used to measure the same dose plane of IMRT treatment plans. The results of the dose map, dose profiles and iso- dose curves were compared with those calculated by CORVUS treatment planning system to evaluate the func- tion of EBT film for dosimetric verification for intensity modulated radiation therapy. Results (1) Over the external beam dosimetric range of 0-500 cGy, EBT/VXR-16 and EDR2/VXR-16 film dosimetric system had the same measurement consistency with the measurement variability less then 0.70%. The mean meas- urement variability of these two systems was 0.37% and 0.68%, respectively. The former proved to be the superior modality at measurement consistency, reliability, and efficiency over dynamic clinical dose range, furthermore, its quality assurance showed less process than the latter. (2) The dosimetric verification of IM- RT plane measured with EBT film was quite similar to that with EDR2 film which was processed under strict quality control. In a plane of the phantom, the maximal dose deviation off axis between EBT film measure ment and the TPS calculation was 3.1%, and for EDR2 film the deviation was 3.6%. With the same de- fined value of DTA and AD, the conformity of pixels meeting the test criteria between the plan and measure- ment was 94.28% and 92.92% for EBT and EDR2 film, respectively. Conclusion EBT radiochromic film based radiation dosimetric system can be applied simply with less quality control process. When com- pared with the radiographic film, the EBT film dosimetric system is more feasible and more reliable for plan- specific dosimetric verification for intensity modulated radiation therapy, which can be extended in chnical application.