This study aimed to compare the dosimetric differences between the craniospinal irradiation (CSI) volumetric modulated arc therapy (VMAT) plan from TrueBream C-arm and Halcyon ring gantry linear accelerator (LINAC).

Ten CSI cases were optimized and calculated on both TrueBeam and Halcyon systems using 6 MV flattening filter-free (FFF) beams. The target prescription dose was 2340 cGy, delivered in 13 fractions. The planning target volume (PTV) and organs at risk (OARs) doses, conformity index (CI), homogeneity index (HI), total normal tissue volume (TNTV) dose, and beam on time were used to analyze the results. The prescribed doses were normalized at 95% of the target volume.

The average D98%, D50%, D2%, CI, and HI of PTV in the TrueBeam plans were 2304.8 ± 16.6 cGy, 2417.7 ± 9.9 cGy, 2490.0 ± 10.2 cGy, 0.90 ± 0.02, and 0.08 ± 0.01, while Halcyon plans showed 2294.0 ± 11.5 cGy, 2424.4 ± 8.2 cGy, 2501.0 ± 19.8 cGy, 0.90 ± 0.02, and 0.09 ± 0.01, respectively. The TNTV at low doses was better in the Halcyon plan. However, 10 of the 16 OARs on the TrueBeam plan had lower doses than the Halcyon plan. The beam on time of TrueBeam plans was 12.01 ± 0.53 min, while Halcyon plans showed 6.10 ± 0.81 min.

TrueBeam plans show statistically better dose coverage and superior OAR sparing. On the other hand, Halcyon performs better in terms of TNTV dose and beam-on time.