title: Comparison of anisotropic aperture based intensity modulated radiotherapy with 3D-conformal radiotherapy for the treatment of large lung tumors.
abstract: OBJECTIVE
  IMRT allows dose escalation for large lung tumors, but respiratory motion may compromise delivery. A treatment plan that modulates fluence predominantly in the transversal direction and leaves the fluence identical in the direction of the breathing motion may reduce this problem.
  
  
  METHODS
  Planning-CT-datasets of 20 patients with Stage I-IV non small cell lung cancer (NSCLC) formed the basis of this study. A total of two IMRT plans and one 3D plan were created for each patient. Prescription dose was 60 Gy to the CTV and 70 Gy to the GTV. For the 3D plans an energy of 18 MV photons was used. IMRT plans were calculated for 6 MV photons with 13 coplanar and with 17 noncoplanar beams. Robustness of the used method of anisotropic modulation toward breathing motion was tested in a 13-field IMRT plan.
  
  
  RESULTS
  As a consequence of identical prescription doses, mean target doses were similar for 3D and IMRT. Differences between 3D and 13- and 17-field IMRT were significant for CTV Dmin (43 Gy vs. 49.1 Gy vs. 48.6 Gy; p<0.001) and CTV D(95) (53.2 Gy vs. 55.0 Gy vs. 55.4 Gy; p=0.001). The D(mean) of the contralateral lung was significantly lower in the 17-field plans (17-field IMRT vs. 13- vs. 3D: 12.5 Gy vs. 14.8 Gy vs. 15.8 Gy: p<0.05). The spinal cord dose limit of 50 Gy was always respected in IMRT plans and only in 17 of 20 3D-plans. Heart D(max) was only marginally reduced with IMRT (3D vs. 13- vs. 17-field IMRT: 38.2 Gy vs. 36.8 Gy vs. 37.8 Gy). Simulated breathing motion caused only minor changes in the IMRT dose distribution (~0.5-1 Gy).
  
  
  CONCLUSIONS
  Anisotropic modulation of IMRT improves dose delivery over 3D-RT and renders IMRT plans robust toward breathing induced organ motion, effectively preventing interplay effects.
authors.affiliation: Department of Radiation Oncology, University of Heidelberg, Mannheim, Germany. anna.simeonova@gmail.com
authors.forename: Anna
authors.initials: A
authors.lastname: Simeonova
authors.forename: Yasser
authors.initials: Y
authors.lastname: Abo-Madyan
authors.forename: Mostafa
authors.initials: M
authors.lastname: El-Haddad
authors.forename: Grit
authors.initials: G
authors.lastname: Welzel
authors.forename: Martin
authors.initials: M
authors.lastname: Polednik
authors.forename: Ramesh
authors.initials: R
authors.lastname: Boggula
authors.forename: Frederik
authors.initials: F
authors.lastname: Wenz
authors.forename: Frank
authors.initials: F
authors.lastname: Lohr
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016880:Anisotropy; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012119:Respiration; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome