title: Vaginal displacement during course of adjuvant radiation for cervical cancer: results from a prospective IG-IMRT study.
abstract: OBJECTIVE
  To compare internal target volume (ITV) generated using population-based displacements (ITV_study) with empty and full bladder scan fusion (ITV_EBFB) for organ-at-risk (OAR) doses during adjuvant intensity-modulated radiation therapy (IMRT) for cervical cancer.
  
  
  METHODS
  From January 2011 to October 2012, patients undergoing IMRT were included. CT simulation was carried out after inserting vault markers. Planning target volume (PTV)_EBFB received 50 Gy per 25 fractions. Pre-treatment megavoltage CT (MVCT) was performed. MVCTs were registered using bony landmarks with Day 1 MVCT. Displacement of the centre of mass of markers was measured along each axis. Directional ITV was calculated using mean ± 2 standard deviations (SDs) (ITV_study). Replanning was performed using PTV study, and OAR doses were compared with PTV_EBFB using Wilcoxon test.
  
  
  RESULTS
  A total of 348/386 data sets were evaluable for 16 patients. The median vaginal displacement was 1.2 mm (SD, 1.3 mm), 4.0 mm (SD, 3.5 mm) and 2.8 mm (SD, 3.3 mm) in the mediolateral, superoinferior and anteroposterior directions, respectively. The ITV margins were 4.1, 10.3 and 10.6 mm. ITV_study and ITV_EBFB were 115.2 cm(3) (87.7-152.2 cm(3)) and 151 cm(3) (95.7-277.1 cm(3)) (p < 0.0001), respectively. PTV_study and PTV_EBFB were 814 and 881 cm(3) (p < 0.0001), respectively. Median doses to the bladder were lower with the PTV_study (46.2 Gy vs 43.2 Gy; p = 0.0001), and a similar trend was observed in the volume of the small bowel receiving 40 Gy (68.2 vs 60.1 cm(3); p = 0.09).
  
  
  CONCLUSIONS
  Population-based PTV margins can lead to reduction in OAR doses.
  
  
  CONCLUSIONS
  Population-based ITV may reduce OAR doses while executing adjuvant IMRT for cervical cancer.
authors.affiliation: 1 Department of Radiation Oncology, Advanced Centre for Treatment, Research and Education in Cancer, Mumbai, Maharashtra, India.
authors.forename: S
authors.initials: S
authors.lastname: Chopra
authors.forename: A
authors.initials: A
authors.lastname: Patidar
authors.forename: T
authors.initials: T
authors.lastname: Dora
authors.forename: N
authors.initials: N
authors.lastname: Moirangthem
authors.forename: S N
authors.initials: SN
authors.lastname: Paul
authors.forename: R
authors.initials: R
authors.lastname: Engineer
authors.forename: U
authors.initials: U
authors.lastname: Mahantshetty
authors.forename: S K
authors.initials: SK
authors.lastname: Shrivastava
mesh_terms: D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D007044:Hysterectomy; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D015641:Radiography, Interventional; D018714:Radiotherapy, Adjuvant; D011882:Radiotherapy, High-Energy; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D001743:Urinary Bladder / Q000000981:diagnostic imaging; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D014621:Vagina / Q000528:radiation effects*