Dose escalation with proton or photon radiation treatment for pancreatic cancer

Purpose: 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 (72 Gy) in pancreatic tumors in different positions relative to organs at risk (OAR) anatomy. Methods and materials: A 3-cm pancreatic tumor was virtually translated every 5 mm over 5 cm 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. Results: 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). Conclusions: Our study showed that the optimal radiation therapy modality for safe dose escalation depends on pancreatic tumor position in relation to OAR anatomy.