Figure 1.

Typical field configurations used to treat pancreatic cancers with protons. A heavily weighted (75% of the target dose) posterior or posterior-oblique field is combined with a more lightly weighted (25% of target dose) right lateral-oblique field. Since the posterior beam is unlikely to pass through an air-filled space on its way to the retroperitoneal target, there is very little uncertainty in its range. Although the treatment plans that include the elective nodes irradiate a larger volume, because of the conformality of the proton dose distribution and posterior location of the target relative to the small bowel space, the elective plans were not associated with meaningfully increased small bowel or gastric exposure compared to the plans treating the gross disease alone. A. Axial (Gross tumor only); B. Coronal (Gross tumor only); C. Sagital (Gross tumor only); D. Axial (Elective nodes included); E. Coronal (Elective nodes included); F. Sagital (Elective nodes included)