title: A dosimetric comparison of proton and photon therapy in unresectable cancers of the head of pancreas.
abstract: OBJECTIVE
  Uncontrolled local growth is the cause of death in ∼ 30% of patients with unresectable pancreatic cancers. The addition of standard-dose radiotherapy to gemcitabine has been shown to confer a modest survival benefit in this population. Radiation dose escalation with three-dimensional planning is not feasible, but high-dose intensity-modulated radiation therapy (IMRT) has been shown to improve local control. Still, dose-escalation remains limited by gastrointestinal toxicity. In this study, the authors investigate the potential use of double scattering (DS) and pencil beam scanning (PBS) proton therapy in limiting dose to critical organs at risk.
  
  
  METHODS
  The authors compared DS, PBS, and IMRT plans in 13 patients with unresectable cancer of the pancreatic head, paying particular attention to duodenum, small intestine, stomach, liver, kidney, and cord constraints in addition to target volume coverage. All plans were calculated to 5500 cGy in 25 fractions with equivalent constraints and normalized to prescription dose. All statistics were by two-tailed paired t-test.
  
  
  RESULTS
  Both DS and PBS decreased stomach, duodenum, and small bowel dose in low-dose regions compared to IMRT (p < 0.01). However, protons yielded increased doses in the mid to high dose regions (e.g., 23.6-53.8 and 34.9-52.4 Gy for duodenum using DS and PBS, respectively; p < 0.05). Protons also increased generalized equivalent uniform dose to duodenum and stomach, however these differences were small (<5% and 10%, respectively; p < 0.01). Doses to other organs-at-risk were within institutional constraints and placed no obvious limitations on treatment planning.
  
  
  CONCLUSIONS
  Proton therapy does not appear to reduce OAR volumes receiving high dose. Protons are able to reduce the treated volume receiving low-intermediate doses, however the clinical significance of this remains to be determined in future investigations.
authors.affiliation: University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Reid F
authors.initials: RF
authors.lastname: Thompson
authors.affiliation: Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
authors.forename: Sonal U
authors.initials: SU
authors.lastname: Mayekar
authors.affiliation: University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Huifang
authors.initials: H
authors.lastname: Zhai
authors.affiliation: University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Stefan
authors.initials: S
authors.lastname: Both
authors.affiliation: University of Washington, Seattle, Washington 98109.
authors.forename: Smith
authors.initials: S
authors.lastname: Apisarnthanarax
authors.affiliation: University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: James M
authors.initials: JM
authors.lastname: Metz
authors.affiliation: University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: John P
authors.initials: JP
authors.lastname: Plastaras
authors.affiliation: University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Edgar
authors.initials: E
authors.lastname: Ben-Josef
mesh_terms: D000368:Aged; D004386:Duodenum / Q000528:radiation effects; D005260:Female; D006801:Humans; D007421:Intestine, Small / Q000528:radiation effects; D007668:Kidney / Q000528:radiation effects; D008099:Liver / Q000528:radiation effects; D008297:Male; D008875:Middle Aged; D010179:Pancreas / Q000473:pathology / Q000528:radiation effects; D010190:Pancreatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D017785:Photons / Q000627:therapeutic use*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated; D013116:Spinal Cord / Q000528:radiation effects; D013270:Stomach / Q000528:radiation effects; D047368:Tumor Burden; D011522:Protons
chemical_list: D011522:Protons