RESUMO
Objective:To investigate the necessity of adaptive re-planning during radiotherapy for nasopharyngeal carcinoma (NPC) and its impact on dose improvement.Methods:Clinical data of 89 NPC patients admitted to Sun Yat-sen University Cancer Center from July 2014 to December 2017 were retrospectively analyzed. All patients received 25+7 rounds of adaptive re-planning during radiotherapy. Plan-A was defined as the initial CT scan-based 25-fraction radiotherapy plan, while plan-B was defined as the re-planned 7-fraction radiotherapy plan based on a subsequent CT scan. The changes in the target and parotid gland volumes were compared between plan-A and plan-B. Plan-I was a one-time simulation of plan-A extended to 32 fraction radiotherapy plan, and plan-II was generated through registration and fusion of the plan-A and plan-B for adaptive re-planning. The differences in dose metrics, homogeneity index (HI), conformity index (CI), and dose to organs at risk (OAR) were compared between plan-I and plan-II. Statistical analysis was performed by using paired t-test. Results:Compared with plan-A, the gross tumor volume of massive bleeding lesions (GTV nx) and parotid gland volume of plan-B were decreased by 13.14% and 11.12%, respectively (both P<0.001). While planning clinical target volume of metastatic lymph nodes (PCTV nd) of plan-B was increased by 7.75%( P<0.001). There were significant changes in the lymph nodes of plan-A and plan-B. The D mean, D 5%, D 95% of massive bleeding lesions planning target volume (PTV nx) and D 5% of high risk planning target volume (PTV1) in plan-II were all significantly higher than those in plan-I (all P<0.05). The CI of PTV nx and PTV1 in plan-II was closer to 1 than that in plan-I. In all assessed OAR, the D mean, D 50%, and D max of plan-II were significantly lower than those of plan-I (all P<0.05). Conclusions:During radiotherapy, NPC patients may experience varying degrees of primary tumor shrinkage, parotid gland atrophy, and lymph node changes. It is necessary to deliver re-planning and significantly improve the dose of target areas and OAR.