(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: To compare the dosimetry of IMRT, non-coplanar IMRT (nc-IMRT) and VMAT treatment plans for pancreatic cancer.
Methods: Treatment plans from 10 patients treated for pancreatic cancer were used for comparison against new sets of treatment plans re-planned with different delivery techniques. All plans were calculated on the Eclipse Treatment Planning System (Varian Medical Systems, Palo Alto, CA) with 6MV energy. The prescription dose was 49.5Gy with 2.75Gy per fraction and optimized with 100% of the prescription dose covering 95% of PTV. The IMRT plans used 7-9 fields. The VMAT plans used two full arcs. The nc-IMRT plans consisted of 5-7 coplanar fields and 2 non-coplanar fields. The organs at risks (OARs) were liver, kidneys, spinal cord, and bowel. The 3 techniques were evaluated base on conformity index (CI), uniformity index (UI), doses to OARs and monitor units (MUs).
Results: The nc-IMRT plans consistently improved kidneys and spinal cord sparing compared to IMRT and VMAT. The averaged mean dose of the total kidney was 6.59Gy for IMRT, 4.07Gy for nc-IMRT and 5.82Gy for VMAT. The nc-IMRT plans were remarkably lower in maximum dose to spinal cord with 15.09Gy compared to 23Gy in IMRT and 25.75Gy in VMAT. However, for bowel, VMAT V15 was reduced by 16.92% and 26.69% compared to IMRT and nc-IMRT respectively. For liver, there were no significant differences among the 3 techniques based on D1/3 and mean dose. The UI for IMRT and nc-IMRT was 1.05 while for VMAT it was 1.03. The CI for 3 techniques was 1.26. The VMAT technique had mostly lower total MUs.
Conclusion: All techniques achieved similar PTV coverage. Although nc-IMRT technique showed better sparing of normal tissues from excess dose, nc-IMRT plans required higher MUs which led to longer delivery time and increased the potential for error due to patient motion.
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