Dose-Volume Histogram Analysis of Stereotactic Body Radiotherapy Treatment of Pancreatic Cancer: A Focus on Duodenal Dose Constraints

Pancreatic carcinoma is an aggressive disease and radiotherapy treatment delivery to the primary tumor is constrained by the anatomical close location of the duodenum, stomach, and small bowel. Duodenal dose tolerance for radiosurgery in 2-5 fractions has been largely unknown. The literature was surveyed for quantitative models of risk in 1-5 fractions and we analyzed our own patient population of 44 patients with unresectable pancreatic tumors who received 3 or 5 fractions of stereotactic body radiotherapy (SBRT) between March 2009 and March 2013. A logistic model was constructed in the dose-volume histogram (DVH) Evaluator software for the duodenal D50%, D30cc, D5cc, D1cc, and maximum point dose D0.035cc. Dose tolerance limits from the literature were overlaid onto the clinical duodenal data in the form of a DVH Risk Map, with risk levels of the published limits estimated from the model of clinical data. In 3 fractions, Kopek 2010 found a statistically significant difference in D1cc of patients with no common terminology criteria for adverse events (CTCAE) v3 grade 2 or higher duodenal complications (mean D1cc = 25.3Gy) as compared with patients with grade 2 or higher toxicity (mean D1cc = 37.4Gy). From the logistic model of our duodenal data in 3 fractions, D1cc = 25.3Gy had 4.7% risk of grade 3-4 hemorrhage or stricture and D1cc = 37.4Gy had 20% risk. The 10% risk level was D1cc = 31.4Gy and we were able to keep duodenum dose for all our patients later this level.