Image-guided determination of actual dose for nasopharyngeal carcinoma patients treated with helical tomotherapy / 中国肿瘤临床

ABSTRACT

Objective:To determine the law of dose variation in nasopharyngeal carcinoma patients treated with helical tomotherapy by observing the difference between the actual and planned doses of targets and at-risk organs in these patients. Methods:Ten naso-pharyngeal carcinoma patients were treated with helical tomotherapy. Each single dose distribution and the corresponding computed tomography (CT) images were transmitted to the commercial software MIMvista 6.50, which was used to perform deformable image registration on the CT images. The sum of the actual dose was then obtained by accumulating the single doses. The image-guided actu-al dose was denoted as Plan 2, and the initial plan was called Plan 1. The dose-volume histogram of the dose distribution of targets and at-risk organs in Plans 1 and 2 were compared. Results:The D98 and D95 doses of the planning gross target volume (PGTV) in Plan 2 were significantly lower than those in Plan 1. Compared with Plan 1, the Dmean and D50 doses of double parotids in Plan 2 were higher by 42.23%and 63.82%(P<0.001, P=0.001) on average, respectively, for the left parotid, as well as by 38.64%and 66.76%(P=0.002, 0.004), respectively, for the right parotid. The D2 dose of spinal cord in Plan 2 was significantly higher than that in Plan 1. The doses were higher by 16.49%on average (P=0.026). Conclusion:To achieve precise and individually adaptive radiotherapy, correcting the error between anatomy and placement during tomotherapy for nasopharyngeal carcinoma patients is necessary.