title: Does VMAT for treatment of NSCLC patients increase the risk of pneumonitis compared to IMRT ? - a planning study.
abstract: BACKGROUND
  Volumetric modulated arc therapy (VMAT) for treatment of non-small cell lung cancer (NSCLC) patients potentially changes the risk of radiation-induced pneumonitis (RP) compared to intensity modulated radiation therapy (IMRT) if the dose to the healthy lung is changed significantly. In this study, clinical IMRT plans were used as starting point for VMAT optimization and differences in risk estimates of RP between the two plan types were evaluated.
  
  
  METHODS
  Fifteen NSCLC patients prescribed 66 Gy in 2 Gy fractions were planned with IMRT and subsequently with single arc VMAT. Dose metrics were evaluated for target and lung together with population averaged dose volume histograms. The risk of RP was calculated using normal tissue complication probability (NTCP) models. Finally, applicability of the plans was tested through delivery on an Elekta accelerator.
  
  
  RESULTS
  When changing from IMRT to VMAT only modest differences were observed in the dose to the lung and target volume. On average, fractions of lung irradiated to doses between 18 Gy and 48 Gy were statistically significant reduced using VMAT compared to IMRT. For the fraction of lung receiving more than 20 Gy the reduction was 1.2% percentage points: (range -0.6 -2.6%). The evaluated toxicity were smaller with VMAT compared to IMRT, however only modest differences were observed in the NTCP values. The plans were delivered without any problems. The average beam on time with VMAT was 83 s. This was a reduction of 141 s (ranging from 37 s to 216 s) compared to IMRT.
  
  
  CONCLUSIONS
  Using IMRT as reference for the VMAT optimization it was possible to implement VMAT in the clinic with no increase in estimated risk of RP. Thus, toxicity is not expected to be a hindrance to using VMAT and will profit from the shorter delivery time with VMAT compared to IMRT.
authors.affiliation: Institute of Clinical Research, University of Southern Denmark, Odense, Denmark. anders.bertelsen@ouh.regionsyddanmark.dk
authors.forename: Anders
authors.initials: A
authors.lastname: Bertelsen
authors.forename: Olfred
authors.initials: O
authors.lastname: Hansen
authors.forename: Carsten
authors.initials: C
authors.lastname: Brink
mesh_terms: D000230:Adenocarcinoma / Q000150:complications / Q000532:radiotherapy*; D000368:Aged; D000369:Aged, 80 and over; D018287:Carcinoma, Large Cell / Q000150:complications / Q000532:radiotherapy*; D002294:Carcinoma, Squamous Cell / Q000150:complications / Q000532:radiotherapy*; D005260:Female; D006258:Head and Neck Neoplasms / Q000150:complications / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D058958:Organs at Risk / Q000528:radiation effects; D011014:Pneumonia / Q000209:etiology*; D011379:Prognosis; D011832:Radiation Injuries / Q000517:prevention & control; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*; D012307:Risk Factors