Room: ePoster Forums
Purpose: Halcyon Version 2 was recently released with new capability to modulate both MLC layers. This makes an effective leaf width of 5 mm though the nominal width is 1 cm. We report our early clinical experience with Halcyon Version 2 for SBRT lung treatments and compare Halcyon with TrueBeam.
Methods: Ten patients with single lung lesions were retrospectively selected. They originally received 48-54 Gy in 3-5 fractions with a 9-field IMRS technique on Halcyon. To compare plan quality between different linacs (Halcyon vs. TrueBeam) and beam arrangements (IMRS vs. VMAT), each patient was replanned with 9-field IMRS for TrueBeam and with 2-arc VMAT for both Halcyon and TrueBeam. Median tumor volume was 19.1 cmÂ³ (range, 9.2-106.2 cmÂ³). Similar optimization objectives were applied for targets and OARs. The plans were normalized to have similar target coverage. These plans were compared for: PTV coverage, spinal cord Dmax, whole lungs V20, conformity index (CI), homogeneity index (HI), gradient index (GI), and total MU. A paired studentâ€™s t-test was performed with a significance level of 0.01.
Results: All Halcyon and TrueBeam plans were similar and clinically acceptable. For Halcyon-IMRS, TrueBeam-IMRS, Halcyon-VMAT, and TrueBeam-VMAT respectively, PTV coverage was 97.3%, 97.3%, 96.8%, 97.1%; spinal cord Dmax was 8.9 Gy, 8.3 Gy, 8.4 Gy, 7.6 Gy; whole lung V20 was 3.3%, 3.5%, 3.2%, 3.1%; CI was 1.07, 1.11, 1.07, 1.08; HI was 1.17, 1.17, 1.18, 1.17; GI was 5.11, 5.25, 4.79, 4.29; and total MU was 3902, 3687, 3539, 3930. All clinical Halcyon-IMRS plans passed QA with an average gamma passing rate of 99.8% (3%/2mm) and an average point dose different of 0.3%.
Conclusion: For single SBRT lung lesions, Halcyon Version 2 demonstrated similar plan quality compared to TrueBeam. Both IMRS and VMAT techniques achieved similar plan quality. Halcyon has great potential for SBRT lung treatments.