TU-E-BRB-07：一种基于电子射野影像装置的高剂量率FFF束立体定向体部放疗剂量验证工具。

TU-E-BRB-07: An EPID Based Dosimetric Verification Tool for SBRT with High Dose Rate FFF Beams.

作者信息

Han B, Luxton G, Bush K, Mok E, Lu M, Xing L

机构信息

Stanford University School of Medicine, Stanford, CA.

Perkin Elmer, Waltham, MA.

出版信息

Med Phys. 2012 Jun;39(6Part24):3909. doi: 10.1118/1.4735956.

DOI:10.1118/1.4735956

PMID:28518679

Abstract

PURPOSE

The increasing use of unflattened high dose rate and/or small sized fields in stereotactic body radiosurgery (SBRT) presents a significant challenge and calls for new tools for dosimetric measurements and quality assurance (QA). The purpose of this work is to investigate a high spatial resolution (0.2mm) and high frame rate (50Hz) amorphous silicon flat-panel electronic portal imaging device (EPID) from Perkin Elmer for SBRT.

METHODS

A Monte Carlo N-Particle eXtended (MCNPX) simulation and convolution based calibration procedure has been developed to derive a voxel-based response function specific to the EPID construct and beam characteristics. Both standard photon beams and flattening filter free (FFF) beams of all energies from Varian TrueBeam STX were studied and the linearity and dose rate dependence were tested. EPID with detailed materials composition was simulated using the MCNPX to generate a scatter kernel composed of dose deposition in the EPID phosphor, and optical photon spreading and to deconvolve the EPID images to high spatial resolution photon fluence map. The fluence map was convolved with MCNPX generated kernels to the 3D dose distribution in the phantom and compared with pinpoint ion chamber and film measurements.

RESULTS

EPID response showed excellent linearity (R2>0.9998) and dose rate dependence less than 1.8% for up to 2400MU/min. Output factors for field sizes ranging from 1×1 to 20×20cm were measured and used to fit the optical photon glare kernel. Fluence profiles deconvolved using MCNPX scattering kernel agrees with the measurements to within 2%. Results of typical pre-treatment QA test exhibit excellent spatial resolution required for SBRT.

CONCLUSIONS

The high spatial resolution and high frame rate EPID proved to be an accurate and efficient tool for SBRT QA. Through convolution with MCNPX scattering core and comprehensive EPID calibration, accurate 3D dose maps can be generated for independent dosimetric verification of SBRT treatments.

摘要

目的

在立体定向体部放射治疗（SBRT）中，未展平的高剂量率和/或小尺寸射野的使用日益增加，这带来了重大挑战，需要新的剂量测量和质量保证（QA）工具。本研究的目的是研究珀金埃尔默公司生产的具有高空间分辨率（0.2mm）和高帧率（50Hz）的非晶硅平板电子射野影像装置（EPID）在SBRT中的应用。

方法

开发了一种基于蒙特卡罗N粒子扩展（MCNPX）模拟和卷积的校准程序，以得出特定于EPID结构和射束特性的基于体素的响应函数。研究了瓦里安TrueBeam STX的所有能量的标准光子射束和无均整器（FFF）射束，并测试了线性度和剂量率依赖性。使用MCNPX模拟具有详细材料组成的EPID，以生成由EPID磷光体中的剂量沉积、光学光子扩散组成的散射核，并将EPID图像反卷积为高空间分辨率的光子注量图。将注量图与MCNPX生成的核进行卷积，得到模体中的三维剂量分布，并与针点电离室和胶片测量结果进行比较。

结果

EPID响应显示出优异的线性度（R2>0.9998），在高达2400MU/min的剂量率下，剂量率依赖性小于1.8%。测量了从1×1到20×20cm射野尺寸的输出因子，并用于拟合光学光子眩光核。使用MCNPX散射核反卷积得到的注量剖面与测量结果的偏差在2%以内。典型的治疗前QA测试结果显示出SBRT所需的优异空间分辨率。