分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： A direct incident fluence measurement method based on amorphous silicon electronic portal imaging device (a-Si EPID) has been developed for pretreatment verification of intensity-modulated radiation therapy (IMRT). The EPID-based incident fluence conversion method deconvolves EPID images to the primary response distribution based on measured lateral scatter kernels in the EPID detector using Conjugate Gradient algorithm. The primary response is converted to the incident fluence based on measured fluence conversion matrix which corrects for off-axis position dependence of the a-Si EPID response and the horn beam profile caused by flatting filter. To verify feasibility and accuracy of this method, square fields of various sizes and two IMRT plans were delivered. The dose distributions computed based on EPID-derived incident fluence were compared with the measurement data. For all square field sizes except the smallest field (2 cm), the mean dose differences in cross-line dose profiles were within 1% excluding the penumbra region, and gamma passing percentages with a 2%/2 mm criterion were about 99%. For two IMRT plans, the least gamma passing percentage for all eight IMRT fields was 98.14% with 2%/3 mm criteria. It can be concluded that our direct EPID-based incident fluence conversion method is accurate and capable of being applied to pretreatment dose verification in clinical routines.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： The absolute dose difference of the iso-center position at different times was used to evaluate the stability of medical linear accelerator (LINAC). In order to eliminate the drawback of point dose without statistical significance and to investigate the output stability of segment with small weight related to intensity-modulated radiotherapy (IMRT), a modified method of evaluating the stability of LINAC was proposed based on planar dose combined with gamma method. With a commercial available two-dimensional ionization chamber, a set of planar doses with dose gradient from 2 cGy to 100 cGy were obtained. Then the gamma method was adopted to analyze the dose difference between the reference data and the evaluated data at each dose level. The results showed that the improved method based on planar dose for analyzing the output stability of the medical LINAC was feasible and efficient, and suggested that the reverse optimization should be aborted in clinical when the segment weight related to IMRT was under 10 MU.
点击量
通过
点击量
下载量
评论
