title: Dosimetric benefit to organs at risk following margin reductions in nasopharyngeal carcinoma treated with intensity-modulated radiation therapy.
abstract: BACKGROUND
  It is important to decrease the radiation exposure of normal tissue in intensity-modulated radiation therapy (IMRT). Minimizing planning target volume (PTV) margins with more precise target localization techniques can achieve this goal. This study aimed to quantify the extent to which organs at risk (OARs) are spared when using reduced margins in the treatment of nasopharyngeal carcinoma (NPC).
  
  
  METHODS
  Two IMRT plans were regenerated for 40 patients with NPC based on two PTV margins, which were reduced or unchanged following cone beam computed tomography online correction. The reduced-margin plan was optimized based on maximal dose reduction to OARs without compromising target coverage. Dosimetric comparisons were evaluated in terms of target coverage and OAR sparing.
  
  
  RESULTS
  Improvements in target coverage occurred with margin reduction, and significant improvements in dosimetric parameters were observed for all OARs (P < 0.05) except for the right optic nerve, chiasm, and lens. Doses to OARs decreased at a rate of 1.5% to 7.7%. Sparing of the left parotid and right parotid, where the mean dose (Dmean) decreased at a rate of 7.1% and 7.7%, respectively, was greater than the sparing of other OARs.
  
  
  CONCLUSIONS
  Significant improvements in OAR sparing were observed with margin reduction, in addition to improvement in target coverage. The parotids benefited most from the online imaging-guided approach.
authors.affiliation: Department of Radiation Oncology, Sun Yat-sen University Cancer Center; State Key Laboratory of Oncology in South China; Collaborative Innovation Center for Cancer Medicine, Guangzhou, Guangdong, 510060, Peoples Republic of China. maoyanzi11@126.com.
authors.forename: Yan-Ping
authors.initials: YP
authors.lastname: Mao
authors.affiliation: Department of Radiation Oncology, Cancer Center of Guangzhou Medical University, Guangzhou, Guangdong, 510095, Peoples Republic of China. wenjing1342@163.com.
authors.forename: Wen-Jing
authors.initials: WJ
authors.lastname: Yin
authors.affiliation: Department of Radiation Oncology, Sun Yat-sen University Cancer Center; State Key Laboratory of Oncology in South China; Collaborative Innovation Center for Cancer Medicine, Guangzhou, Guangdong, 510060, Peoples Republic of China. guorui@sysucc.org.cn.
authors.forename: Rui
authors.initials: R
authors.lastname: Guo
authors.affiliation: Department of Radiation Oncology, Sun Yat-sen University Cancer Center; State Key Laboratory of Oncology in South China; Collaborative Innovation Center for Cancer Medicine, Guangzhou, Guangdong, 510060, Peoples Republic of China. zgs0218@163.com.
authors.forename: Guang-Shun
authors.initials: GS
authors.lastname: Zhang
authors.affiliation: Department of Radiation Oncology, Sun Yat-sen University Cancer Center; State Key Laboratory of Oncology in South China; Collaborative Innovation Center for Cancer Medicine, Guangzhou, Guangdong, 510060, Peoples Republic of China. fangjl@sysucc.org.cn.
authors.forename: Jian-Lan
authors.initials: JL
authors.lastname: Fang
authors.affiliation: Department of Radiation Oncology, Sun Yat-sen University Cancer Center; State Key Laboratory of Oncology in South China; Collaborative Innovation Center for Cancer Medicine, Guangzhou, Guangdong, 510060, Peoples Republic of China. chifeng@sysucc.org.cn.
authors.forename: Feng
authors.initials: F
authors.lastname: Chi
authors.affiliation: Department of Radiation Oncology, Sun Yat-sen University Cancer Center; State Key Laboratory of Oncology in South China; Collaborative Innovation Center for Cancer Medicine, Guangzhou, Guangdong, 510060, Peoples Republic of China. qizhy@sysucc.org.cn.
authors.forename: Zhen-Yu
authors.initials: ZY
authors.lastname: Qi
authors.affiliation: Department of Radiation Oncology, Sun Yat-sen University Cancer Center; State Key Laboratory of Oncology in South China; Collaborative Innovation Center for Cancer Medicine, Guangzhou, Guangdong, 510060, Peoples Republic of China. liumzh@sysucc.org.cn.
authors.forename: Meng-Zhong
authors.initials: MZ
authors.lastname: Liu
authors.affiliation: Department of Radiation Oncology, Sun Yat-sen University Cancer Center; State Key Laboratory of Oncology in South China; Collaborative Innovation Center for Cancer Medicine, Guangzhou, Guangdong, 510060, Peoples Republic of China. majun2@mail.sysu.edu.cn.
authors.forename: Jun
authors.initials: J
authors.lastname: Ma
authors.affiliation: Department of Radiation Oncology, Sun Yat-sen University Cancer Center; State Key Laboratory of Oncology in South China; Collaborative Innovation Center for Cancer Medicine, Guangzhou, Guangdong, 510060, Peoples Republic of China. sunying2@mail.sysu.edu.cn.
authors.forename: Ying
authors.initials: Y
authors.lastname: Sun
mesh_terms: D002277:Carcinoma; D006801:Humans; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms; D058958:Organs at Risk; D010306:Parotid Gland; D000069079:Radiation Exposure; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated