胶片剂量测量和验证方法的研究

Development of film dosimetric measurement system for verification of RTP

目的设计和实现基于通用激光扫描仪的胶片剂量测量和验证系统。方法采用胶片饱和冲洗、非线性光学校正、多分辨率阈值滤波、离散傅里叶逆变换图像复原等方法,消除了普通扫描仪用于胶片剂量学定量处理中的各种伪影、噪声和畸变;采用过响应系数校正方法消除测量胶片对低能散射光子的过响应,改善了胶片剂量测量的准确性;采用γ结合NAT指标的方法对放疗计划进行二维定量验证,给出可视化图形表达和具有定量数据的验证结果。结果和三维水箱系统、VeriSoft胶片测量系统相比较,研制系统对放疗剂量的测量结果在±2%内符合一致,对IMRT放疗计划的定量验证结果在±3%内符合一致。结论该系统能够实现对放疗剂量的高精度测量和对适形调强放疗计划剂量的可靠验证。

Objective To develop a novel film dosimetry system based on general laser scanner in order to verify patient-specific Radiotherapy Treatment Plan （RTP） in three-Dimensional Adaptable Radiotherapy （3D ART） and Intensity Modulated Radiotherapy （IMRT）. Methods Some advanced methods, including film saturated development, wavelet filtering with multi-resolution thresholds and discrete Fourier reconstruction are employed in this system to reduce artifacts, noise and distortion induced by film digitizing with general scanner; a set of coefficients derived from Monte Carlo（MC） simulation are adopted to correct the film over-response to low energy scattering photons; a set of newly emerging criteria, including T index and Normalized Agreement Test （NAT） method, are employed to quantitatively evaluate agreement of 2D dose distributions between the results measured by the films and calculated by Treatment Planning System （TPS）, so as to obtain straightforward presentations, displays and results with high accuracy and reliability, Results Radiotherapy doses measured by developed system agree within 2% with those measured by ionization chamber and VeriSofi Film Dosimetry System, and quantitative evaluation indexes are within 3%. Conclusions The developed system can be used to accurately measure the radiotherapy dose and reliablely make quantitative evaluation for RTP dose verification.