Clinical-target-volume to planning-target-volume margin evaluation in head-and-neck cancer VMAT using cone beam computed tomography
Abstract
Background and Objective: The interfraction setup variation may affect the precision of radiotherapy. The aim of this study was to analyse the interfraction variation of head-and-neck cancer patients who were treated with VMAT technique by using cone beam CT (CBCT). The data was used to define adequate treatment CTV-to-PTV margin. Material and method: During June 2013 to June 2015, the CBCT data was collected from 109 headand- neck cancer patients treated with VMAT from Varian Clinac 23EX. The CBCT images were registered to the planning CT images and setup error on X, Y and Z direction were recorded Result: A total of 509 CBCT from 110 patients were collected. Systematic error in vertical, longitudinal and lateral directions were 0.89 mm, 0.98 mm and 1.01 mm, respectively, and the random error in vertical, longitudinal and lateral directions were 1.49 mm, 1.59 mm and 1.50 mm, respectively. Calculated CTV-to- PTV margins by using the Van Herk formula in vertical, longitudinal and lateral direction were 3.27 mm, 3.56 mm and 3.56 mm, respectively. Conclusion: The CTV-to-GTV margins were less than 5 mm, thus the margin ensured adequate coverage for all patients and can apply these margins for improving efficiency and reduction of side effects of radiotherapy.
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