Abstract
BackgroundRespiratory motion may introduce errors during radiotherapy. This study aims to assess and validate internal gross tumour volume (IGTV) margins in different regions in gastroesophageal junction (GEJ) tumours during simultaneous integrated boost radiotherapy.MethodsWe enrolled 10 patients in group A and 9 patients in group B. For all patients, two markers were placed at the upper and lower boundaries of tumour before treatment. In group A, within the simulation and every five fractions of radiotherapy, we used 4-dimensional computed tomography (4DCT) to record the intrafractional displacement of the proximal and distal markers. By fusing the average image of each fraction with the simulation image according to the lumbar vertebra, the interfractional displacement could be obtained. We calculated the IGTV margin in the proximal and distal regions of the GEJ tumour. In group B, by referring to the simulation images and cone-beam computed tomography (CBCT) images, the range of tumour displacement in different regions within the GEJ tumour was estimated. We verified the proportion of tumours with marker displacement within the range obtained in group A to estimate the accuracy of the IGTV margin.ResultsThe intrafractional displacement in the cranio-caudal (CC) direction was significantly larger than that in the anterior-posterior (AP) and left-right (LR) directions for both the proximal and distal markers of the tumour. The interfractional displacement in the AP and LR directions was larger than that in the CC direction (p=0.001, p=0.017) according to the distal marker. The IGTV margins for in the LR, AP and CC directions were 9 mm, 8.5 mm and 12.1 mm for proximal marker and 15.8 mm, 12.7 mm and 11.5 mm for distal marker. In group B, the proportions of tumours that fell within the IGTV margin in the LR, AP and CC directions were 96.5%, 91.3% and 96.5% for the proximal marker and 100%, 96.5%, 93.1% for the distal marker.ConclusionsOur study proposed individualized IGTV margins for different regions within GEJ tumours during neoadjuvant radiotherapy. The IGTV margin determined in this study was relatively small and was validated appropriately. It could be a reference in clinical practice.
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