Title: Analysis of online cone beam CT images for nasopharyngeal carcinoma to define appropriate CTV-to-PTV margins
Abstract: OBJECTIVE:To investigate the magnitude of the setup error using online kilo-voltage cone beam computed tomography(kV CBCT) for nasopharyngeal carcinoma,and estimate the appropriate margins for the planning target volume(PTV).METHODS:Sixteen nasopharyngeal carcinoma patients underwent 3D CRT or IMRT.Immobilization and alignment were performed by conventional head-and-neck masking and laser alignment for daily positioning.kV CBCT scans were acquired on couch before radiotherapy.The analysis of these images was performed by automatic and manual registration of the kV CBCT and planning CT images.The patient setup was then corrected by moving the couch accordingly.CBCT online-guided correction data were recorded.RESULTS:A total of 160 CBCT sets of 16 nasopharyngeal carcinoma patients were analyzed.If the goal of treatment was clinical target volumes that received the prescribed dose was 95% at least,the margins required to account for these setup errors were 4 mm in the right-left,superior-inferior,anterior-posterior directions,respectively.CONCLUSIONS:There exists some extent of setup error in nasopharyngeal carcinoma 3D CRT or IMRT.The approach based on the CBCT measurements can be used to reduce the impact of setup error obviously and to estimate the required margins for PTV.
Publication Year: 2009
Publication Date: 2009-01-01
Language: en
Type: article
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