Using MVCT image evaluates dose accuracy of treatment planning with metal implants

• Main Authors: Yi-Ting Chen, 陳依婷
• Other Authors: Wen-Tao Huang
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/33739300119449294480

碩士 === 元培醫事科技大學 === 放射技術研究所 === 103 === With advanced medical material science, the use of metal prosthesis has increasingly become popular. Metal implants produce severe scattering artifact on kilo-voltage computed tomography (kVCT). It makes the imaging distortion of soft tissue and deviation from the accuracy of dose calculation. To correct the defect, mega-voltage computer tomography (MVCT) reduces metal-induced scattering. By creating new CT density table, this study tested MVCT for assisting kVCT image to better delineate soft tissue, accurately calculate dose, and improve quality of treatment plan. In the first part, by using cheese phantom, tissue equivalent plugs and metal rods were acquired by kVCT (control) and MVCT (experimental). Regions of interest were contoured for dose calculation and measurement. With appropriate CT numbers, repeated verifications generated new density table. The same treatment plans with different energies between kVCT and MVCT images were compared for the dose distributions. In the second part, the simulation images by kVCT and MVCT of two prostate cancer patients with hip prosthesis and vertebral metastasis, as well as a nasopharyngeal patient with metal implant were compared for dose distributions. kVCT has low noise and good resolution for soft tissue with low CT density but not high CT density. The high noise of MVCT leads to a relatively large dose errors. The comparison of the dose measurement on phantom showed less than 3% difference in low-density tissues. The dose measurements of ferroalloy and cerrobend showed more than 5% difference by 6-MV energy, and of only cerrobend showed more than 5% difference on 10-MV energy. In patients’ plans comparing dose distributions by single beam, dose curves on kVCT went deeper than MVCT. In comparison of multiple beams for high dose distribution, MVCT was close to kVCT. For low-dose distribution MVCT showed less dose depth than kVCT. To compare the images, kVCT is good for the resolution of low–density tissue, while MVCT has no scattering artifact in high-density tissue. The integration of MVCT with the modified CT density table improves the dose accuracy and quality of the treatment plan of patients with metal implants.