title: The effect of multileaf collimator leaf width on the radiosurgery planning for spine lesion treatment in terms of the modulated techniques and target complexity.
abstract: OBJECTIVE
  We aim to evaluate the effects of multileaf collimator (MLC) leaf width (5 mm vs. 2.5 mm) on the radiosurgery planning for the treatment of spine lesions according to the modulated techniques (intensity-modulated radiotherapy [IMRT] vs. volumetric-modulated arc therapy [VMAT]) and the complexity of the target shape.
  
  
  METHODS
  For this study, artificial spinal lesions were contoured and used for treatment plans. Three spinal levels (C5, T5, and L2 spines) were selected, and four types of target shapes reflecting the complexity of lesions were contoured. The treatment plans were performed using 2.5-mm and 5-mm MLCs, and also using both static IMRT and VMAT. In total, 48 treatment plans were established. The efficacy of each treatment plan was compared using target volume coverage (TVC), conformity index (CI), dose gradient index (GI), and V(30%).
  
  
  RESULTS
  When the 5-mm MLC was replaced by the 2.5-mm MLC, TVC and GI improved significantly by 5.68% and 6.25%, respectively, while CI did not improve. With a smaller MLC leaf width, the improvement ratios of the TVC were larger in IMRT than VMAT (8.38% vs. 2.97%). In addition, the TVC was improved by 14.42-16.74% in target type 4 compared to the other target types. These improvements were larger in IMRT than in VMAT (27.99% vs. 6.34%). The V(30%) was not statistically different between IMRT and VMAT according to the MLC leaf widths and the types of target.
  
  
  CONCLUSIONS
  The smaller MLC leaf width provided improved target coverage in both IMRT and VMAT, and its improvement was larger in IMRT than in VMAT. In addition, the smaller MLC leaf width was more effective for complex-shaped targets.
authors.forename: Soo-Min
authors.initials: SM
authors.lastname: Chae
authors.forename: Gi Woong
authors.initials: GW
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, Incheon St, Mary's hospital, College of Medicine, the Catholic University of Korea, Incheon, Korea. sonshyun@catholic.ac.kr.
authors.forename: Seok Hyun
authors.initials: SH
authors.lastname: Son
mesh_terms: D006801:Humans; D058958:Organs at Risk; D011874:Radiometry; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods; D013116:Spinal Cord / Q000473:pathology; D013125:Spinal Neoplasms / Q000473:pathology / Q000601:surgery*; D047368:Tumor Burden