Quality Characteristics for Effective Source to Surface Distance of LINAC Electron Beam

• Main Authors: CHUNG, CHAO-CHI, 鐘兆麒
• Other Authors: PAN, LUNG-KWANG
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/8h6n34

碩士 === 中臺科技大學 === 醫學影像暨放射科學系暨研究所 === 105 === Quality characteristics for effective source to surface distance (SSD) of LINAC electron beam were evaluated in this work. In some cases of extended SSD, output cannot be accurately predicted by using the inverse square law from the nominal source position (X-ray target) because the electrons scatter from various locations such as the scattering foils, the X-ray jaws, and the electron applicator. For most cases of clinical significance, however, the output can be accurately predicted by using the inverse square law from an effective source position. The distance from this effective source position to the patient surface is called the "effective SSD" (SSDeff) and is well known to be a function of beam energy and cone size. We had determined the dependence of SSDeff on various combinations of cone size, and beam energy. An Axesse 6D LINAC was adopted and the four operated factors: beam energy, cone size, dmax, and gap were preset into 3-26 levels, respectively in this work. Thus a total of 6×3×6×26=2808 combinations was considered and condensed to only 207 trials of effective measurements according to Taguchi’s optimal recommendation. Each trial was measured three times to reduce the error and ensure the reproducibility. The derived data were then integrated altogether to compose a 1st-order nonlinear semi-empirical formula with 11 coefficients. The summarized uncertainties were suppressed to below 5 % for the estimation. The comparison between theoretical and practical evaluations was depicted and the correlated discussion were also emphasized point by point to imply the importance of this revised evaluation in clinical field.