Dose escalation with proton or photon radiation treatment for pancreatic cancer

The purpose was to determine the optimal radiation therapy modality (three-dimensional conformal photon-radiation therapy [3DCRT], intensity-modulated photon-radiation therapy [IMRT], or passive-scattering proton therapy [PT]) for safe dose escalation (72Gy) in pancreatic tumors in different positions relative to organs at risk (OAR) anatomy.

A 3-cm pancreatic tumor was virtually translated every 5mm over 5cm laterally. We generated two plans for each of the three techniques (3DCRT, IMRT, and PT), one that adhered to target coverage objectives and another to meet OAR sparing constraints with best coverage. We evaluated distances between gross tumor volumes and isodoses and compared dose-volume histograms.

IMRT was more conformal in higher gradient dose regions circumferentially, but tumor positions with anteriorly located small bowel benefited more from PT. 3DCRT plans resulted in inadequate target coverage. The V(15Gy) (mean+/-SD) were as follows for the IMRT and PT plans, respectively: stomach, 48%+/-4% vs 5%+/-3% (p<0.0001); and small bowel, 61%+/-8% vs 9%+/-4% (p<0.0001).

Our study showed that the optimal radiation therapy modality for safe dose escalation depends on pancreatic tumor position in relation to OAR anatomy.