title: Proton therapy may allow for comprehensive elective nodal coverage for patients receiving neoadjuvant radiotherapy for localized pancreatic head cancers.
abstract: BACKGROUND
  Neoadjuvant radiotherapy has the potential to improve local disease control for patients with localized pancreatic cancers. Concern about an increased risk of surgical complications due to small bowel and gastric exposure, however, has limited enthusiasm for this approach. Dosimetric studies have demonstrated the potential for proton therapy to reduce intestinal exposure compared with X-ray-based therapy. We sought to determine if neoadjuvant proton therapy allowed for field expansions to cover high-risk nodal stations in addition to the primary tumor.
  
  
  METHODS
  Twelve consecutive patients with nonmetastatic cancers of the pancreatic head underwent proton-based planning for neoadjuvant radiotherapy. Gross tumor volume was contoured using diagnostic computed tomography (CT) scans with oral and intravenous contrast. Four-dimensional planning scans were utilized to define an internal clinical target volume (ICTV). Five-mm planning target volume (PTV) expansions on the ICTV were generated to establish an initial PTV (PTV1). A second PTV was created using the initial PTV but was expanded to include the high-risk nodal targets as defined by the RTOG contouring atlas (PTV2). Optimized proton plans were generated for both PTVs for each patient. All PTVs received a dose of 50.4 cobalt gray equivalent (CGE). Normal-tissue exposures to the small bowel space, stomach, right kidney, left kidney and liver were recorded. Point spinal cord dose was limited to 45 CGE.
  
  
  RESULTS
  Median PTV1 volume was 308.75 cm(3) (range, 133.33-495.61 cm(3)). Median PTV2 volume was 541.75 cm(3) (range, 399.44-691.14 cm(3)). In spite of the substantial enlargement of the PTV when high-risk lymph nodes were included in the treatment volume, normal-tissue exposures (stomach, bowel space, liver, and kidneys) were only minimally increased relative to the exposures seen when only the gross tumor target was treated.
  
  
  CONCLUSIONS
  Proton therapy appears to allow for field expansions to cover high-risk lymph nodes without significantly increasing critical normal-tissue exposure in the neoadjuvant setting.
authors.affiliation: Radiation Medicine, Roswell Park Cancer Institute, University at Buffalo, NY, USA;
authors.forename: Richard Y
authors.initials: RY
authors.lastname: Lee
authors.forename: Romaine C
authors.initials: RC
authors.lastname: Nichols
authors.forename: Soon N
authors.initials: SN
authors.lastname: Huh
authors.forename: Meng W
authors.initials: MW
authors.lastname: Ho
authors.forename: Zuofeng
authors.initials: Z
authors.lastname: Li
authors.forename: Robert
authors.initials: R
authors.lastname: Zaiden
authors.forename: Ziad T
authors.initials: ZT
authors.lastname: Awad
authors.forename: Bestoun
authors.initials: B
authors.lastname: Ahmed
authors.forename: Bradfors S
authors.initials: BS
authors.lastname: Hoppe
keywords: Proton therapy; dosimetry; neoadjuvant radiotherapy; pancreatic