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Intracranial Stereotactic Radiosurgery Treatment Planning Technique Comparison: Volumetric-Modulated Arc Therapy Vs. Dynamic Conformal Arc Therapy Or Static Field Intensity Modulated Radiotherapy

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T Tseng

T Tseng*, R Sheu , S Green , Y Lo , Mount Sinai Medical Center, New York, NY


SU-I-GPD-T-571 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To compare intracranial SRS treatment plan quality between volumetric-modulated arc therapy (VMAT) and dynamic conformal arc (DCA)/static field intensity modulated radiotherapy (IMRT).

Methods: Twelve patients with fifteen cranial lesions (0.08 – 14.95 cc) planned with DCA (n=10) or IMRT (n=5) in iPlan® (PBC, m3 MLC) were selected and re-planned with VMAT in Eclipse® (AAA, Millennium 120 MLC). DCA, IMRT and VMAT plan were generated with 4-6 coplanar/non-coplanar arcs, 8-11 fields, and 5-6 coplanar/non-coplanar arcs, respectively. VMAT plans were optimized to meet original plan coverage indices: GTV minimum dose (99.7±0.5%) and maximum dose (113.2±0.6%). Plan quality is evaluated with dosimetrical parameters: conformity index (CI-RTOG and CI-Paddick) and Gradient Index (GI).Total MU of each technique was also evaluated.

Results: The average CI-RTOG and CI-Paddick of DCA plans, 1.42±0.15 and 0.71±0.06, are slightly better than that of VMAT plans, 1.62±0.29 and 0.63±0.10. The average GI of VMAT plans, 4.68±2.04, is superior to DCA plans, 5.84±3.24. As for the comparison between IMRT and VMAT plans, average CI-RTOG and CI-Paddick of IMRT plans, 1.33±0.07 and 0.72±0.04 are better than VMAT plans, 1.49±0.25 and 0.65±0.08. However, the average GI of VMAT plans, 4.25±0.57, is improved compare to IMRT plans, 4.93±0.92. Average total MU of DCA and VMAT plans are 2572±439 vs. 5874±1262; and 3060±396 vs. 5165±938 for IMRT and VMAT plans. Although DCA/IMRT plans were found to have preferred conformity than VMAT plans, the differences decrease when lesion size increases. Better gradient index shows the dose fall-off from 100% to 50% is quicker in VMAT plans, but the difference also decreases with lesion size.

Conclusion: Our study shows DCA and IMRT plans have better conformity compared to VMAT plans, but the difference decreases as lesion size increases. Conversely VMAT plans are capable of providing better dose fall-off, particularly for smaller lesions.

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