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Radiation Oncology

, 8:277

Radiation Physics


BackgroundTo investigate the feasibility and benefits of a modified adaptive radiotherapy ART by replanning in the initial CT iCT with new contours from a repeat CT rCT based on CT-CT image fusion for nasopharyngeal cancer NPC patients underwent volumetric modulated arc radiotherapy VMAT.

Materials and methodsNine NPC patients underwent VMAT treatment with a rCT at 23rd fraction were enrolled in this study. Dosimetric differences for replanning VMAT plans in the iCT and in the rCT were compared. Volumetric and dosimetric changes of gross tumor volume GTV and organs at risk OARs of this modified ART were also investigated.

ResultsNo dosimetric differences between replanning in the iCT and in the rCT were observed. The average volume of GTV decreased from 78.83 ± 38.42 cm in the iCT to 71.44 ± 37.46 cm in the rCT, but with no significant difference p = 0.42.The average volume of the left and right parotid decreased from 19.91 ± 4.89 cm and 21.58 ± 6.16 cm in the iCT to 11.80 ± 2.79 cm and 13.29 ± 4.17 cm in the rCT both p < 0.01, respectively. The volume of other OARs did not shrink very much. No significant differences on PTVGTV and PTVCTV coverage were observed for replanning with this modified ART. Compared to the initial plans, the average mean dose of the left and right parotid after re-optimization were decreased by 62.5 cGy p = 0.05 and 67.3 cGy p = 0.02, respectively, and the V5 the volume receiving 5 Gy of the left and right parotids were decreased by 7.8% p = 0.01 and 11.2% p = 0.001, respectively. There was no significant difference on the dose delivered to other OARs.

ConclusionPatients with NPC undergoing VMAT have significant anatomic and dosimetric changes to parotids. Repeat CT as an anatomic changes reference and re-optimization in the iCT based on CT-CT image fusion was accurate enough to identify the volume changes and to ensure safe dose to parotids.

KeywordsNasopharyngeal cancer Adaptive radiotherapy Volumetric modulated arc therapy CT-CT image fusion Deformable registration Electronic supplementary materialThe online version of this article doi:10.1186-1748-717X-8-277 contains supplementary material, which is available to authorized users.

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Autor: Xiance Jin - Ce Han - Yongqiang Zhou - Jinling Yi - Huawei Yan - Congying Xie

Fuente: https://link.springer.com/

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