Dosimetric Comparison of Different Pattern of Intensity-modulated Radiotherapy for Pancreatic Carcinoma

  Objective  To analyze the dosimetric differences between fixed-field intensity-modulated radiotherapy (FF-IMRT) and volumetric modulated arc therapy (VMAT) in treating pancreatic carcinoma, aiming to facilitate the clinical decision upon appropriate radiation technique.

  Methods  From June to December 2011, 10 postoperative patients of pancreatic carcinoma who received radiotherapy in Peking Union Medical College Hospital were selected for this comparison. FF-IMRT and VMAT plans were developed based on the same CT simulation image for each patient. The prescription dose was 50 Gy in 25 fractions. The doses distributions in planning target volume (PTV), organs at risk (OARs), and normal tissue were evaluated based on dose-volume histograms (DVH). The two plans were also compared in terms of monitor unit (MU) and length of treatment.

  Results  The dose distributions in PTV showed no significant difference between FF-IMRT and VMAT plans(P > 0.05). Compared with FF-IMRT plan, VMAT plan significantly increased V₅ of the liver, stomach, small intestine, and whole body(all P < 0.05), while reduced V₁₀ and V₂₀ of the liver, V₁₀ of the stomach, V₁₀, V₂₀, and V₅₀ of the small intestine, V₂₀ of the left kidney, V₂₀, V₃₀, D_mean, D_max of the right kidney, and V₁₀, V₂₀ of the whole body (all P < 0.05). The D_max of the spinal cord decreased by 1.85 Gy in VMAT plan (P=0.04). MU of VMAT plan was significantly lower than that of FF-IMRT plan (492.70±51.56 vs. 619±117.18, t=3.18, P=0.01), with a 20.48% reduction from the MU level of the latter one.

  Conclusion  For patients with pancreatic carcinoma, VMAT plan could reduce MU and shorten length of treatment while maintaining the dosimetric parameters at levels similar to or even better than those of FF-IMRT plan.