A treatment planning evaluation of protons versus IMRT in pancreatic cancer: A comparative study.

369 Background: The purpose of this study is to investigate dose distributions of proton and intensity-modulated radiation therapy (IMRT) photon treatment plans in patients with resected pancreatic adenocarcinoma, focusing specifically on dose reduction to the kidney, liver, and small bowel as organs at risk. Methods: Ten patients with pancreatic head adenocarcinoma underwent Whipple procedure between 2010 and 2013 were included in this study. Most of the patients had locally advanced disease (T 3-4 N 1 ). All patients were simulated with contrast-enhanced CT imaging. The clinical target volume (CTV) consisted of the pre-operative extent of tumor plus a 10 mm manual expansion in all directions. The planning target volume (PTV) was generated by a further expansion on the CTV ranging from 10-15 mm. A dose of 50.4 Gy given in 28 fractions was delivered to the PTV. All plans were optimized to allow 95% isodose coverage of at least 95% of the PTV. Dose-volume histograms, conformity index (CI), uniformity index (UI), homogeneity index (HI), were calculated and analyzed in order to compare plans between the two modalities. The OAR being evaluated in this study are the kidneys, liver, small bowel, and spinal cord. To determine statistical significance, ANOVA and two-tailed paired t-tests were performed for all data parameters. Results: The proton plans resulted in a lower mean kidney dose (3.17 Gy vs. 9.59 Gy, p=0.039), a lower dose delivered to 1/3 of the liver, D 1/3 , (0.25 Gy vs. 4.56 Gy, p=0.003), and a lower mean liver dose (1.83 Gy vs. 5.24 Gy, p=0.021). See table for a summary of the results. Conclusions: For patients receiving postoperative radiotherapy for pancreatic cancer, the proton plans are technically feasible and dosimetrically appealing with superior organ at risk sparing compared to IMRT photon treatment plans.[Table: see text]