title: Dosimetric comparison of intensity-modulated stereotactic radiotherapy with other stereotactic techniques for locally recurrent nasopharyngeal carcinoma.
abstract: OBJECTIVE
  Locally recurrent nasopharyngeal carcinoma (NPC) patients can be salvaged by reirradiation with a substantial degree of radiation-related complications. Stereotactic radiotherapy (SRT) is widely used in this regard because of its rapid dose falloff and high geometric precision. The aim of this study was to examine whether the newly developed intensity-modulated stereotactic radiotherapy (IMSRT) has any dosimetric advantages over three other stereotactic techniques, including circular arc (CARC), static conformal beam (SmMLC), and dynamic conformal arc (mARC), in treating locally recurrent NPC.
  
  
  METHODS
  Computed tomography images of 32 patients with locally recurrent NPC, previously treated with SRT, were retrieved from the stereotactic planning system for contouring and computing treatment plans. Treatment planning of each patient was performed for the four treatment techniques: CARC, SmMLC, mARC, and IMSRT. The conformity index (CI) and homogeneity index (HI) of the planning target volume (PTV) and doses to the organs at risk (OARs) and normal tissue were compared.
  
  
  RESULTS
  All four techniques delivered adequate doses to the PTV. IMSRT, SmMLC, and mARC delivered reasonably conformal and homogenous dose to the PTV (CI <1.47, HI <0.53), but not for CARC (p < 0.05). IMSRT presented with the smallest CI (1.37) and HI (0.40). Among the four techniques, IMSRT spared the greatest number of OARs, namely brainstem, temporal lobes, optic chiasm, and optic nerve, and had the smallest normal tissue volume in the low-dose region.
  
  
  CONCLUSIONS
  Based on the dosimetric comparison, IMSRT was optimal for locally recurrent NPC by delivering a conformal and homogenous dose to the PTV while sparing OARs.
authors.affiliation: State Key Laboratory in Oncology in South China, Sir Y K Pao Centre for Cancer, Department of Clinical Oncology, Hong Kong Cancer Institute, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Shiris Wai Sum
authors.initials: SW
authors.lastname: Kung
authors.forename: Vincent Wing Cheung
authors.initials: VW
authors.lastname: Wu
authors.forename: Michael Koon Ming
authors.initials: MK
authors.lastname: Kam
authors.forename: Sing Fai
authors.initials: SF
authors.lastname: Leung
authors.forename: Brian Kwok Hung
authors.initials: BK
authors.lastname: Yu
authors.forename: Dennis Yuen Kan
authors.initials: DY
authors.lastname: Ngai
authors.forename: Simon Chun Fai
authors.initials: SC
authors.lastname: Wong
authors.forename: Anthony Tak Cheung
authors.initials: AT
authors.lastname: Chan
mesh_terms: D002277:Carcinoma; D006801:Humans; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy / Q000601:surgery; D009364:Neoplasm Recurrence, Local / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D058958:Organs at Risk / Q000528:radiation effects; D011859:Radiography; D016634:Radiosurgery / Q000379:methods; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013238:Stereotaxic Techniques; D047368:Tumor Burden