title: Interfractional variation in position of the uterus during radical radiotherapy for cervical cancer.
abstract: OBJECTIVE
  This study was conducted to investigate the positional change of the uterus during radiotherapy which can degrade the accuracy of three-dimensional conformal radiotherapy (3DCRT) and intensity modulated radiotherapy (IMRT).
  
  
  METHODS
  Sixty-six patients received radical radiotherapy for cervical cancer in Samsung Medical Center. For each patient, two MRI scans were taken; one was before beginning radiotherapy and the other was in the third or fourth week of radiotherapy. In T2-weighted MRI images, the positional change of the uterus was quantified by measuring six parameters; the distance from the external uterine opening to the isthmus of the uterus (Dcx), the distance from the isthmus of the uterus to the uterine fundus (Dco), the perpendicular distance of the uterine body to the uterine corpus (Dco-per), the angle between the vertical line and the cervical canal in sagittal images (Acx), the uterine corpus angle from the vertical line in sagittal plan (Aco), the angle between the uterine corpus from an arbitrary bony landmark and a vertical mid line in axial images (Aco-axi)
  
  
  RESULTS
  Mean value of change in Dcx+Dco of tumor size during treatment was 8.0 mm in small tumors and 17.9 mm in large tumors. Among 44 anteflexed uterus patients, 5 changed into a retroflexed position. 12 patients (18%) had a greater than 30 degrees variation in any angle. For patients under 60 years, the difference in Acx was statistically significant.
  
  
  CONCLUSIONS
  Positional changes of the uterus during radiotherapy should be considered in the treatment planning of 3DCRT or IMRT, particularly in patients under 60 years or those with tumor size greater than 4 cm in diameter.
authors.affiliation: Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Ilwon-Dong 50, Kangnam-ku, 135-710 Seoul, South Korea.
authors.forename: Seung Jae
authors.initials: SJ
authors.lastname: Huh
authors.forename: Won
authors.initials: W
authors.lastname: Park
authors.forename: Youngyih
authors.initials: Y
authors.lastname: Han
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002584:Cervix Uteri / Q000473:pathology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal; D002583:Uterine Cervical Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D014599:Uterus / Q000473:pathology*