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Evaluation of Best Dosimetry Achievable with VMAT and IMRT Treatment Techniques Targeting Borderline Resectable Pancreatic Cancer

K Harpool

K Harpool*, E Schnell , T Herman , S Ahmad , T De La Fuente Herman , University of Oklahoma Health Sciences Center, Oklahoma City, OK


SU-F-T-395 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To determine from retrospective study the most appropriate technique for targeting small borderline operable pancreatic cancer surrounding blood vessels by evaluating the dosimetry and normal tissue sparing achievable using Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT).

Methods: Treatment plans from ten patients who have undergone treatment with a prescribed dose of 4950 cGy, at 275 cGy per fraction, were analyzed. All plans were re-planned using Eclipse TPS (Varian Medical Systems, Palo Alto, CA) with complementary VMAT or IMRT techniques to obtain paired data sets for comparison. The coverage to at least 95% of the planned target volume (PTV) was normalized to receive 100% of the prescription dose. The normal tissue constraints followed the quantitative analysis of normal tissue effects in the clinic (QUANTEC) guidelines and the organs at risks (OARs) were liver, kidneys, spinal cord and bowel. The plan evaluation was based on conformity index (CI), homogeneity index (HI), uniformity index (UI), DVH parameters, and student’s-t statistics (2 tails).

Results: The VMAT technique delivered less maximum dose to the right kidney, left kidney, total kidney, liver, spinal cord, and bowel by 9.3%, 5.9%, 6.7%, 3.9%, 15.1%, 3.9%, and 4.3%, respectively. The averaged V15 for the total kidney was 10.21% for IMRT and 7.29% for VMAT. The averaged V20 for the bowel was 19.89% for IMRT and 14.06% for VMAT. On average, the CI for IMRT was 1.20 and 1.16 for VMAT (p = 0.20). The HI was 0.08 for both techniques (p = 0.91) and UI was 1.05 and 1.06 for IMRT and VMAT respectively (p = 0.59).

Conclusion: Both techniques achieve adequate PTV coverage. Although VMAT techniques show better normal tissue sparing from excessive dose, no significant differences were observed. Slight discrepancies may rise from different versions of calculation algorithms.

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