title: Clinical decision tool for optimal delivery of liver stereotactic body radiation therapy: Photons versus protons.
abstract: OBJECTIVE
  Stereotactic body radiation therapy (SBRT) for treatment of liver tumors is often limited by liver dose constraints. Protons offer potential for more liver sparing, but clinical situations in which protons may be superior to photons are not well described. We developed and validated a treatment decision model to determine whether liver tumors of certain sizes and locations are more suited for photon versus proton SBRT.
  
  
  METHODS
  Six spherical mock tumors from 1 to 6 cm in diameter were contoured on computed tomography images of 1 patient at 4 locations: dome, caudal, left medial, and central. Photon and proton plans were generated to deliver 50 Gy in 5 fractions to each tumor and optimized to deliver equivalent target coverage and maximal liver sparing. Using these plans, we developed a hypothesis-generating model to predict the optimal modality for maximal liver sparing based on tumor size and location. We then validated this model in 10 patients with liver tumors.
  
  
  RESULTS
  Protons spared significantly more liver than photons for dome or central tumors ≥3 cm (dome: 134 ± 21 cm(3), P = .03; central: 108 ± 4 cm(3), P = .01). Our model correctly predicted the optimal SBRT modality for all 10 patients. For patients with dome or central tumors ≥3 cm, protons significantly increased the volume of liver spared (176 ± 21 cm(3), P = .01) and decreased the mean liver dose (8.4 vs 12.2 Gy, P = .01) while offering no significant advantage for tumors <3 cm at any location or for caudal and left medial tumors of any size.
  
  
  CONCLUSIONS
  When feasible, protons should be considered as the radiation modality of choice for dome and central tumors >3 cm to allow maximal liver sparing and potentially reduce radiation toxicity. Protons should also be considered for any tumor >5 cm if photon plans fail to achieve adequate coverage or exceed the mean liver threshold.
authors.affiliation: University of Pennsylvania, Department of Radiation Oncology, Philadelphia, Pennsylvania.
authors.forename: Saumil J
authors.initials: SJ
authors.lastname: Gandhi
authors.affiliation: University of Pennsylvania, Department of Radiation Oncology, Philadelphia, Pennsylvania.
authors.forename: Xing
authors.initials: X
authors.lastname: Liang
authors.affiliation: University of Pennsylvania, Department of Radiation Oncology, Philadelphia, Pennsylvania.
authors.forename: Xuanfeng
authors.initials: X
authors.lastname: Ding
authors.affiliation: University of Pennsylvania, Department of Radiation Oncology, Philadelphia, Pennsylvania.
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Zhu
authors.affiliation: University of Pennsylvania, Department of Radiation Oncology, Philadelphia, Pennsylvania.
authors.forename: Edgar
authors.initials: E
authors.lastname: Ben-Josef
authors.affiliation: University of Pennsylvania, Department of Radiation Oncology, Philadelphia, Pennsylvania.
authors.forename: John P
authors.initials: JP
authors.lastname: Plastaras
authors.affiliation: University of Pennsylvania, Department of Radiation Oncology, Philadelphia, Pennsylvania.
authors.forename: James M
authors.initials: JM
authors.lastname: Metz
authors.affiliation: University of Pennsylvania, Department of Radiation Oncology, Philadelphia, Pennsylvania.
authors.forename: Stefan
authors.initials: S
authors.lastname: Both
authors.affiliation: University of Pennsylvania, Department of Radiation Oncology, Philadelphia, Pennsylvania; Currently at University of Washington, Department of Radiation Oncology, Seattle, Washington. Electronic address: apisarn@uw.edu.
authors.forename: Smith
authors.initials: S
authors.lastname: Apisarnthanarax
mesh_terms: D003198:Computer Simulation; D006801:Humans; D008099:Liver / Q000473:pathology* / Q000601:surgery*; D008113:Liver Neoplasms / Q000601:surgery*; D008962:Models, Theoretical; D059351:Organ Sparing Treatments / Q000379:methods*; D017785:Photons / Q000627:therapeutic use; D061766:Proton Therapy; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed; D011522:Protons
chemical_list: D011522:Protons