Room: Exhibit Hall | Forum 7
Purpose: To compare plan quality and delivery efficiency of non-coplanar VMAT (NC-VMAT) with coplanar VMAT (C-VMAT), IMRT and CyberKnife (CK) plans for multiple brain metastases.
Methods: For 15 brain metastases patients, NC-VMAT, C-VMAT, IMRT and CK plans with a prescription dose of 30 Gy in 3 fractions were generated. NC-VMAT and C-VMAT plans consisted of 4 non-coplanar arcs and 2 full coplanar arcs, respectively. IMRT plans were designed with 7 coplanar fields. All plans were generated to cover 95% volume of the planning target volume with the prescription dose. Gradient index (GI), conformity index (CI), normal brain tissue volume (V3 Gy-V24 Gy), monitor units (MUs) and beam on time (BT) were evaluated.
Results: GI was the lowest for CK (3.49Â±0.65), followed by NC-VMAT (4.21Â±1.38), C-VMAT (4.87Â±1.35) and IMRT (5.36Â±1.98). CI was the largest for NC-VMAT (0.87Â±0.03), followed by C-VMAT (0.86Â±0.04), CK (0.86Â±0.07) and IMRT (0.85Â±0.05). Normal brain tissue volume at high-to-moderate dose spreads (V24 Gy-V9 Gy) was significantly reduced in NC-VMAT over that of IMRT and C-VMAT. Normal brain tissue volume for NC-VMAT was comparable with CK at high dose level (V24 Gy-V15 Gy) and larger than CK at moderate-to-low dose level (V12 Gy-V3 Gy). MUs was highest for CK (28733.59Â±7197.85), followed by IMRT (4128.40Â±1185.38), NC-VMAT (3105.20Â±371.23) and C-VMAT (2997.27Â±446.84). BT was longest for CK (30.25Â±7.32 min), followed by IMRT (2.95Â±0.85 min), NC-VMAT (2.61Â±0.07 min) and C-VMAT (2.30Â±0.23 min).
Conclusion: NC-VMAT plans generated rapid dose falloff and high conformity compared with IMRT and C-VMAT plans. NC-VMAT plans provided a comparable dose falloff with CK plans at high dose level and a slower dose falloff than CK plans at moderate-to-low dose level. NC-VMAT plans had less MUs and shorter BT than CK plans.
Funding Support, Disclosures, and Conflict of Interest: This study was supported by National natural Science Foundation of China (81071237) and Interdisciplinary Medicine Seed Fund of Peking University (BMU20160585)