title: Improve definition of titanium tandems in MR-guided high dose rate brachytherapy for cervical cancer using proton density weighted MRI.
abstract: BACKGROUND
  For cervical cancer patients treated with MR-guided high dose rate brachytherapy, the accuracy of radiation delivery depends on accurate localization of both tumors and the applicator, e.g. tandem and ovoid. Standard T2-weighted (T2W) MRI has good tumor-tissue contrast. However, it suffers from poor uterus-tandem contrast, which makes the tandem delineation very challenging. In this study, we evaluated the possibility of using proton density weighted (PDW) MRI to improve the definition of titanium tandems.
  
  
  METHODS
  Both T2W and PDW MRI images were obtained from each cervical cancer patient. Imaging parameters were kept the same between the T2W and PDW sequences for each patient except the echo time (90 ms for T2W and 5.5 ms for PDW) and the slice thickness (0.5 cm for T2W and 0.25 cm for PDW). Uterus-tandem contrast was calculated by the equation C=(Su-St)/Su, where Su and St represented the average signal in the uterus and the tandem, respectively. The diameter of the tandem was measured 1.5 cm away from the tip of the tandem. The tandem was segmented by the histogram thresholding technique.
  
  
  RESULTS
  PDW MRI could significantly improve the uterus-tandem contrast compared to T2W MRI (0.42±0.24 for T2W MRI, 0.77±0.14 for PDW MRI, p=0.0002). The average difference between the measured and physical diameters of the tandem was reduced from 0.20±0.15 cm by using T2W MRI to 0.10±0.11 cm by using PDW MRI (p=0.0003). The tandem segmented from the PDW image looked more uniform and complete compared to that from the T2W image.
  
  
  CONCLUSIONS
  Compared to the standard T2W MRI, PDW MRI has better uterus-tandem contrast. The information provided by PDW MRI is complementary to those provided by T2W MRI. Therefore, we recommend adding PDW MRI to the simulation protocol to assist tandem delineation process for cervical cancer patients.
authors: Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, Missouri, USA. yhu@radonc.wustl.edu
authors: Yanle
authors: Y
authors: Hu
authors: Jacqueline
authors: J
authors: Esthappan
authors: Sasa
authors: S
authors: Mutic
authors: Susan
authors: S
authors: Richardson
authors: Hiram A
authors: HA
authors: Gay
authors: Julie K
authors: JK
authors: Schwarz
authors: Perry W
authors: PW
authors: Grigsby
mesh_terms: D001918:Brachytherapy; D005260:Female; D006801:Humans; D007089:Image Enhancement; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D011379:Prognosis; D061766:Proton Therapy; D061089:Radiotherapy, Image-Guided; D012189:Retrospective Studies; D014025:Titanium / Q000737:chemistry*; D002583:Uterine Cervical Neoplasms / Q000473:pathology / Q000532:radiotherapy*
chemical_list: D014025:Titanium