title: Adaptive stereotactic body radiation therapy planning for lung cancer.
abstract: OBJECTIVE
  To investigate the dosimetric effects of adaptive planning on lung stereotactic body radiation therapy (SBRT).
  
  
  METHODS
  Forty of 66 consecutive lung SBRT patients were selected for a retrospective adaptive planning study. CBCT images acquired at each fraction were used for treatment planning. Adaptive plans were created using the same planning parameters as the original CT-based plan, with the goal to achieve comparable comformality index (CI). For each patient, 2 cumulative plans, nonadaptive plan (PNON) and adaptive plan (PADP), were generated and compared for the following organs-at-risks (OARs): cord, esophagus, chest wall, and the lungs. Dosimetric comparison was performed between PNON and PADP for all 40 patients. Correlations were evaluated between changes in dosimetric metrics induced by adaptive planning and potential impacting factors, including tumor-to-OAR distances (dT-OAR), initial internal target volume (ITV1), ITV change (ΔITV), and effective ITV diameter change (ΔdITV).
  
  
  RESULTS
  34 (85%) patients showed ITV decrease and 6 (15%) patients showed ITV increase throughout the course of lung SBRT. Percentage ITV change ranged from -59.6% to 13.0%, with a mean (±SD) of -21.0% (±21.4%). On average of all patients, PADP resulted in significantly (P=0 to .045) lower values for all dosimetric metrics. ΔdITV/dT-OAR was found to correlate with changes in dose to 5 cc (ΔD5cc) of esophagus (r=0.61) and dose to 30 cc (ΔD30cc) of chest wall (r=0.81). Stronger correlations between ΔdITV/dT-OAR and ΔD30cc of chest wall were discovered for peripheral (r=0.81) and central (r=0.84) tumors, respectively.
  
  
  CONCLUSIONS
  Dosimetric effects of adaptive lung SBRT planning depend upon target volume changes and tumor-to-OAR distances. Adaptive lung SBRT can potentially reduce dose to adjacent OARs if patients present large tumor volume shrinkage during the treatment.
authors.affiliation: Medical Physics Graduate Program, Duke University, Durham, North Carolina, USA.
authors.forename: Yujiao
authors.initials: Y
authors.lastname: Qin
authors.forename: Fan
authors.initials: F
authors.lastname: Zhang
authors.forename: David S
authors.initials: DS
authors.lastname: Yoo
authors.forename: Chris R
authors.initials: CR
authors.lastname: Kelsey
authors.forename: Fang-Fang
authors.initials: FF
authors.lastname: Yin
authors.forename: Jing
authors.initials: J
authors.lastname: Cai
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D019583:Dose Fractionation, Radiation; D004947:Esophagus / Q000000981:diagnostic imaging / Q000528:radiation effects; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000528:radiation effects; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000528:radiation effects; D035441:Thoracic Wall / Q000000981:diagnostic imaging / Q000528:radiation effects; D047368:Tumor Burden / Q000528:radiation effects