Abstract：Objective To compare the dosimetric effects of simulation and correction fusion (SF), automatic and visual correction fusion (AF), and bone fusion (BF) during the course of intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). Methods Fifteen patients with stage III-IVa NPC treated with IMRT had planning CT scans before and after 20-25 fractions of radiotherapy. SF, AF, and PF methods were separately used to undertake the fusion between the first and second planning CT images. New treatment isocenters were the shadow cast of the initial isocenter on the second planning CT images with the three fusion methods;initial treatment planning was transferred to the second planning CT according the new treatment isocenter, and new dosimetric distribution was calculated. The fusion parameters of the three fusion methods, as well as dosimetric changes in the target volume and normal tissue, were compared with paired t-test. Results There were relatively small differences in fusion parameters between SF and AF methods;the paired difference means in translation in all directions were less than 0.13 cm, and the paired difference means in rotation in all directions were less than 0.40 degree. BF fusion parameters differed widely from others, especially in rotation, and the paired difference means were more than 0.71 degree. The three fusion methods have similar dosimetric effects on the target volume and normal tissue,but had a significant dosimetric effect on the neck region, with a significant decrease in GTVnd D95(P=0.039). Dmax and D1 cm3 for the brain stem remained unchanged or showed an increasing trend with the BF method, but they showed a decreasing trend with the SF and AF methods. Conclusions Different fusion methods would lead to different results in the research on dosimetric changes in the target volume and normal tissueduring the IMRT for NPC, so the fusion method should be introduced in the reports of these research. TheBF method is not recommended because its dosimetric effect on the neck region is great, resulting in a big DOI:10.3760/cma.j.issn.1004-4221.2015.03.018 基金项目:北京希望马拉松专项基金资助(LC2012B36) 作者单位:100021 北京协和医学院 中国医学科学院肿瘤医院放疗科 通信作者:高黎,Email:li_gao2008@outlook.comdifference from the actual dose distribution. The SF and AF methods have similar dosimetric effects, which are close to the actual situation.
. Dosimetric effects of different fusion methods during intensity-modulated radiotherapy for nasopharyngeal carcinoma[J]. Chinese Journal of Radiation Oncology, 2015, 24(3): 301-305.
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