title: Determining appropriate timing of adaptive radiation therapy for nasopharyngeal carcinoma during intensity-modulated radiation therapy.
abstract: BACKGROUND
  To determine appropriate timing of an adaptive radiation therapy (ART) replan by evaluating anatomic and dosimetric changes of target volumes and organs at risk (OARs) during intensity-modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC).
  
  
  METHODS
  Nineteen NPC patients were recruited. Each patient had repeat computed tomography (CT) scans after each five fractions and at treatment completion. Automatic re-contouring the targets and OARs by using deformable registration algorithm was conducted through CT-CT fusion. Anatomic changes were assessed by comparing the initial CT and repeated CT. Hybrid plans with re-contouring were generated and the dose-volume histograms (DVH) of the hybrid plan and the original plan were compared.
  
  
  RESULTS
  Progressive volume reductions in gross target volume for primary disease (GTVnx), gross target volume for involved lymph nodes (GTVnd), and parotids were observed over time. Comparing with the original plan, each hybrid plan had no significant difference in homogeneity index (HI) for all the targets. Some parameters for planning target volumes for primary disease and high-risk clinical target volume (PTVnx and PTV1, respectively) improved significantly, notably starting from the 10th fraction. These parameters included mean dose (Dmean), dose to 95% of the volume (D95), percentage of the volume receiving 95% of the prescription dose (V95), and conformity index (CI) for PTVnx, and Dmean, D95, and CI for PTV1. The dosimetric parameters for PTVnd remained the same in general except for D95 and V95 which had significant improvement at specific time points; whereas for PTV2, similar trend of dosimetric changes was also observed. Dose to some OARs increased significantly at some time points.
  
  
  CONCLUSIONS
  There were significant anatomic and dosimetric changes in the targets and OARs. The target dose coverage in the hybrid plans did not get worse, but overdose occurred in some critical structures. Significant dosimetric changes should be considered as a trigger point at which ART replanning is indicated. D95/V95/CI for PTV2, Dmax for the brain stem, spinal cord, right eyeball and left lens, and Dmean/V30 for the parotids and glottis were taken into account for predicting the need for ART. Two replans at the 5th and 15th fractions were suggested.
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. huang.huixian@163.com.
authors.forename: Huixian
authors.initials: H
authors.lastname: Huang
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. luhming3632@163.com.
authors.forename: Heming
authors.initials: H
authors.lastname: Lu
authors.affiliation: Department of Medical Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. fengguosheng88988@163.com.
authors.forename: Guosheng
authors.initials: G
authors.lastname: Feng
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. jianghailan198823@163.com.
authors.forename: Hailan
authors.initials: H
authors.lastname: Jiang
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. cjx166@yahoo.com.cn.
authors.forename: Jiaxin
authors.initials: J
authors.lastname: Chen
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. chengjinjian1028@sina.com.
authors.forename: Jinjian
authors.initials: J
authors.lastname: Cheng
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. pangqiang453237@163.com.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Pang
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. 1844587481@qq.com.
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Lu
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. gujunzhao1005@hotmail.com.
authors.forename: Junzhao
authors.initials: J
authors.lastname: Gu
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. luxingpeng20642@163.com.
authors.forename: Luxing
authors.initials: L
authors.lastname: Peng
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. dengshan@163.com.
authors.forename: Shan
authors.initials: S
authors.lastname: Deng
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. ying_mo28964@163.com.
authors.forename: Ying
authors.initials: Y
authors.lastname: Mo
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. danling_wu@yahoo.com.cn.
authors.forename: Danling
authors.initials: D
authors.lastname: Wu
authors.affiliation: Departments of Radiation Oncology, People's Hospital of Guangxi Zhuang Autonomous Region, Nanning, China. 182884158@qq.com.
authors.forename: Yinglin
authors.initials: Y
authors.lastname: Wei
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D002277:Carcinoma; D059248:Chemoradiotherapy / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D058958:Organs at Risk / Q000528:radiation effects*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013997:Time Factors; D055815:Young Adult