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Craniospinal irradiation planning and delivery: a comparison between Halcyon Ring Gantry and TrueBeam C Arm LINAC
Venugopal Sundaram1,2, D Khanna1, P Mohandass3
1Division of Physical Sciences, Karunya Institute of Technology and Sciences, Coimbatore, India.
Background:
This research assesses the dosimetric differences in volumetric modulated arc therapy (VMAT) between True- BeamTM C-arm and Halcyon™ ring gantry linacs, specifically for craniospinal irradiation (CSI) treatment.
Materials And Methods:
The fifteen patients retrospectively chosen for this study were treated with the TrueBeam linear accelerator between 2020 and 2023. Initially, VMAT patient plans were planned and delivered in TrueBeam (TB6X), and using the same objective function, TB6FFF and Halcyon™ (HAL6FFF) plans were generated. Plans were compared dosimetrically using dose volume histogram (DVH) parameters for the cranial, spine targets and Organs At Risk (OARs) in the treatment planning system (TPS). The different dose dosimetric criteria were evaluated such as dose received by D98%, D95%, D50%, D 1cc, volume receiving ≥ 107% dose, max dose (Gy), homogeneity index (HI), conformity index (CI), Monitor Units (MU) and dose spillage [V20Gy, V10Gy, V5Gy, V2Gy (%), DBody - planning target volume (PTV)]. Delivery accuracy was evaluated by performing pre-treatment Portal Dosimetry (PD) measurements applied with 3%/2 mm acceptance criteria and a 95% passing rate.
Results:
Brain PTV dose received by 95% of the PTV volume (D95% (Gy) PTV) for TB6X, TB6FFF, and HAL6FFF plans were 35.9 ± 0.3 Gy, 35.7 ± 0.4 Gy, and 35.6 ± 0.4 Gy respectively and the difference was statistically insignificant (paired sample t-test). Spine PTV dose D95% in the same sequence, 35.7 ± 0.3 Gy, 35.5 ± 0.6 Gy, and 35.4 ± 0.3 Gy with a statistically significant difference (p = 0.016) for TB6X vs. HAL6FFF. Brain PTV HI for TB6X, TB6FFF, and HAL6FFF were 0.07 ± 0.03, 0.08 ± 0.03, and 0.09 ± 0.02, respectively, and in the same sequence, Spine PTV 0.07 ± 0.01, 0.08 ± 0.02 and 0.09 ± 0.02. MUs for TB6X, TB6FFF, and HAL6FFF plans were 1004.9 ± 97.7, 1454.3 ± 197.9, and 1195.8 ± 204.7, respectively, with a mean difference of 449.4, 190.9 and 258.5 MUs and found statistically significant (p < 0.005).
Conclusions:
Clinically and dosimetrically acceptable VMAT-based craniospinal irradiation plans can be generated by the newly introduced dual-layer Multi-Leaf Collimator (MLC) model in a Halcyon™ linac.
