title: A margin-of-the-day online adaptive intensity-modulated radiotherapy strategy for cervical cancer provides superior treatment accuracy compared to clinically recommended margins: a dosimetric evaluation.
abstract: OBJECTIVE
  To dosimetrically evaluate a margin-of-the-day (MoD) online adaptive intensity-modulated radiotherapy (IMRT) strategy for cervical cancer patients. The strategy is based on a single planning computed tomography (CT) scan and a pretreatment constructed IMRT plan library with incremental clinical target volumes (CTV)-to-planning target volumes (PTV) margins.
  
  
  METHODS
  For 14 patients, 9-10 variable bladder filling CT scans acquired at pretreatment and after 40 Gy were available. Bladder volume variability during the treatment course was recorded by twice-weekly US bladder-volume measurements. A MoD strategy that selects the best IMRT plan of the day from a library of plans with incremental margins in steps of 5 mm was compared with a clinically recommended population-based margin (15 mm). To compare the strategies, for each fraction that had a recorded US bladder-volume measurement, the CT scan with the nearest bladder volume was selected from the pretreatment CT series and from the CT series acquired after 40 Gy. A frequency-weighted average of the dose-volume histograms (DVH) parameters calculated for the two selected CT scans was used to estimate the DVH parameters of the fraction of interest.
  
  
  RESULTS
  The 15-mm recommended margin resulted in cervix-uterus underdosage in six of 14 patients. Compared with the 15-mm margin, the MoD strategy resulted in significantly better cervix-uterus coverage (p = 0.008) without a significant difference in the sparing of rectum, bladder, and small bowel. For each patient, 3-8 (median 5) plans were needed in the library of plans for the MoD strategy. The required range of the MoD was 5-45 mm (median 15 mm). Twenty-five percent of all fractions could be treated with a MoD of 5 mm and 81% of all fractions could be treated with a MoD up to 25 mm.
  
  
  CONCLUSIONS
  Compared with a clinically recommended margin, a simple online adaptive strategy resulted in better cervix-uterus coverage without compromising organs at risk sparing.
authors.affiliation: Department of Radiation Oncology, Erasmus MC-Daniel den Hoed Cancer Center , Rotterdam , The Netherlands.
authors.forename: Rozilawati
authors.initials: R
authors.lastname: Ahmad
authors.forename: Luiza
authors.initials: L
authors.lastname: Bondar
authors.forename: Peter
authors.initials: P
authors.lastname: Voet
authors.forename: Jan-Willem
authors.initials: JW
authors.lastname: Mens
authors.forename: Sandra
authors.initials: S
authors.lastname: Quint
authors.forename: Glenn
authors.initials: G
authors.lastname: Dhawtal
authors.forename: Ben
authors.initials: B
authors.lastname: Heijmen
authors.forename: Mischa
authors.initials: M
authors.lastname: Hoogeman
mesh_terms: D005260:Female; D006801:Humans; D009367:Neoplasm Staging; D009862:Online Systems; D058958:Organs at Risk / Q000528:radiation effects; D011379:Prognosis; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted; D061089:Radiotherapy, Image-Guided; D050397:Radiotherapy, Intensity-Modulated; D012007:Rectum / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed; D001743:Urinary Bladder / Q000000981:diagnostic imaging; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*