title: Dosimetric evaluation of anatomical changes during treatment to identify criteria for adaptive radiotherapy in oesophageal cancer patients.
abstract: BACKGROUND
  Some oesophageal cancer patients undergoing chemotherapy and concomitant radiotherapy (chemoRT) show large interfractional anatomical changes during treatment. These changes may modify the dose delivered to the target and organs at risk (OARs). The aim of the presenwt study was to investigate the dosimetric consequences of anatomical changes during treatment to obtain criteria for an adaptive RT decision support system.
  
  
  METHODS
  Twenty-nine patients were treated with chemoRT for oesophageal and gastro-oesophageal junction cancer and set up according to daily cone beam computed tomography (CBCTs) scans. All patients had an additional replanning CT scan at median fraction number 10 (9-14), which was deformably registered to the original planning CT. Gross tumour volumes (GTVs), clinical target volumes (CTVs) and OARs were transferred to the additional CT and corrected by an exwperienced physician. Treatment plans were recalculated and dose to targets and OARs was evaluated. Treatment was adapted if the volume receiving 95% of the prescribed dose (V95%) coverage of CTV decreased > 1% or planning target volume (PTV) decreased by > 3%.
  
  
  RESULTS
  In total, nine adaptive events were observed: All nine were triggered by PTV V95% decrease > 3% [median 11% (5-41%)] and six of these were additionally triggered by CTV V95% decrease > 1% [median 5% (2-35%)]. The largest discrepancies were caused by interfractional baseline or amplitude shifts in diaphragm position (n = 5). Mediastinal (n = 6), oesophageal (n = 6) and bowel filling changes (n = 2) caused the remainder of the changes. For patients with dosimetric changes exceeding the adaptation limits, the discrepancies were confirmed by inspecting the daily CBCTs. In 31% of all patients, heart V30Gy increased more than 2% (maximum 5%). Only minor changes in lung dose or liver dose were seen.
  
  
  CONCLUSIONS
  Target coverage throughout the course of chemoRT treatment is compromised in some patients due to interfractional anatomical changes. Dose to the heart may increase as well.
authors.affiliation: a Department of Medical Physics , Aarhus University Hospital , Denmark.
authors.forename: Tine Bisballe
authors.initials: TB
authors.lastname: Nyeng
authors.affiliation: b Department of Oncology , Aarhus University Hospital , Denmark.
authors.forename: Marianne
authors.initials: M
authors.lastname: Nordsmark
authors.affiliation: a Department of Medical Physics , Aarhus University Hospital , Denmark.
authors.forename: Lone
authors.initials: L
authors.lastname: Hoffmann
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D054893:Cone-Beam Computed Tomography; D004938:Esophageal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D004943:Esophagogastric Junction / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011874:Radiometry; D061089:Radiotherapy, Image-Guided; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*