title: 4π noncoplanar stereotactic body radiation therapy for centrally located or larger lung tumors.
abstract: OBJECTIVE
  To investigate the dosimetric improvements in stereotactic body radiation therapy for patients with larger or central lung tumors using a highly noncoplanar 4π planning system.
  
  
  METHODS
  This study involved 12 patients with centrally located or larger lung tumors previously treated with 7- to 9-field static beam intensity modulated radiation therapy to 50 Gy. They were replanned using volumetric modulated arc therapy and 4π plans, in which a column generation method was used to optimize the beam orientation and the fluence map. Maximum doses to the heart, esophagus, trachea/bronchus, and spinal cord, as well as the 50% isodose volume, the lung volumes receiving 20, 10, and 5 Gy were minimized and compared against the clinical plans. A dose escalation study was performed to determine whether a higher prescription dose to the tumor would be achievable using 4π without violating dose limits set by the clinical plans. The deliverability of 4π plans was preliminarily tested.
  
  
  RESULTS
  Using 4π plans, the maximum heart, esophagus, trachea, bronchus and spinal cord doses were reduced by 32%, 72%, 37%, 44%, and 53% (P≤.001), respectively, and R50 was reduced by more than 50%. Lung V20, V10, and V5 were reduced by 64%, 53%, and 32% (P≤.001), respectively. The improved sparing of organs at risk was achieved while also improving planning target volume (PTV) coverage. The minimal PTV doses were increased by the 4π plans by 12% (P=.002). Consequently, escalated PTV doses of 68 to 70 Gy were achieved in all patients.
  
  
  CONCLUSIONS
  We have shown that there is a large potential for plan quality improvement and dose escalation for patients with larger or centrally located lung tumors using noncoplanar beams with sufficient quality and quantity. Compared against the clinical volumetric modulated arc therapy and static intensity modulated radiation therapy plans, the 4π plans yielded significantly and consistently improved tumor coverage and critical organ sparing. Given the known challenges in central structure dose constraints in stereotactic body radiation therapy to the lung, 4π planning may increase efficacy and reduce toxicity.
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA 90095, USA.
authors.forename: Peng
authors.initials: P
authors.lastname: Dong
authors.forename: Percy
authors.initials: P
authors.lastname: Lee
authors.forename: Dan
authors.initials: D
authors.lastname: Ruan
authors.forename: Troy
authors.initials: T
authors.lastname: Long
authors.forename: Edwin
authors.initials: E
authors.lastname: Romeijn
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Low
authors.forename: Patrick
authors.initials: P
authors.lastname: Kupelian
authors.forename: John
authors.initials: J
authors.lastname: Abraham
authors.forename: Yingli
authors.initials: Y
authors.lastname: Yang
authors.forename: Ke
authors.initials: K
authors.lastname: Sheng
mesh_terms: D000465:Algorithms; D001980:Bronchi / Q000528:radiation effects; D004947:Esophagus / Q000528:radiation effects; D006321:Heart / Q000528:radiation effects; D006801:Humans; D008168:Lung / Q000528:radiation effects; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D059351:Organ Sparing Treatments / Q000379:methods; D058958:Organs at Risk / Q000528:radiation effects*; D011832:Radiation Injuries / Q000517:prevention & control*; D011859:Radiography; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D013116:Spinal Cord / Q000528:radiation effects; D014132:Trachea / Q000528:radiation effects; D047368:Tumor Burden