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Ying Cao,1,* Du Tang,1,* Yining Xiang,1 Li Men,2 Chao Liu,1 Qin Zhou,1 Jun Wu,3 Lei Huo,3 Tao Song,3 Ying Wang,4 Zhanzhan Li,1 Rui Wei,1 Liangfang Shen,1 Zhen Yang,1 Jidong Hong1 1Department of Oncology, Xiangya Hospital, Central South University, Changsha, Hunan, People’s Republic of China; 2Department of Radiology, Xiangya Hospital, Central South University, Changsha, Hunan, People’s Republic of China; 3Department of Neurosurgery, Xiangya Hospital, Central South University, Changsha, Hunan, People’s Republic of China; 4Department of Pathology, Xiangya Hospital, Central South University, Changsha, Hunan, People’s Republic of China*These authors contributed equally to this workCorrespondence: Jidong HongDepartment of Oncology, Xiangya Hospital, Central South University, No. 87, Xiangya Road, Changsha, Hunan, 410008, People’s Republic of ChinaTel +86 731 8975 3733Fax +86 731 8975 3336Email hongjidong1966@126.comPurpose: To investigate the appropriate timing of adaptive radiotherapy (ART) for high-grade glioma.Methods: Ten patients with high-grade gliomas were selected and underwent CT/MRI (CT1/MRI1, CT2/MRI2, CT3/MRI3, and CT4/MRI4) scans before RT and during 10-, 20- and 30-fraction RT, and the corresponding RT plans (plan1, plan2, plan3 and plan4) were made. The dose of the initial plan (plan1) was projected to CT2 and CT3 using the image registration technique to obtain the projection plans (plan1– 2 and plan1– 3) and by superimposing the doses to obtain the ART plans (plan10+20 and plan20+10), respectively. The dosimetric differences in the target volume and organs at risk (OARs) were compared between the projection and adaptive plans. The tumor control probability (TCP) for the planning target volume (PTV) and normal tissue complication probability (NTCP) for the OARs were compared between the two adaptive plans.Results: Compared with the projection plan, the D2 to the PTV of ART decreased, the conformity index (CI) to the PTV increased, and the D2/Dmean to the brainstem, optic chiasm and pituitary, as well as the V20, V30, V40 and V50 to the normal brain decreased. The D2 to the pituitary and optic chiasm as well as the V20, V30, V40 and V50 to the normal brain in plan10+20 were lower than those in plan20+10, while the CI to the PTV was higher than that in plan20+10. The TCP of the PTV in plan10+20 was higher than that in plan20+10.Conclusion: ART can improve the precision of target volume irradiation and reduce the irradiation dose to the OARs in high-grade glioma. The time point after 10 fractions of RT is appropriate for ART.Keywords: adaptive radiotherapy, high-grade glioma, dosimetry, biophysical model