Room: Exhibit Hall | Forum 7
Purpose: To investigate the utility of template trajectories generated by classifying the human brain into different anatomical regions and compare them to the standard VMAT template for cranial stereotactic radiotherapy that does not rely on anatomy. Arc placement optimization was achieved using 4Ï€ techniques.
Methods: Template trajectories were constructed based on the open source Montreal Neurological Institute (MNI) average brain. The MNI brain was populated with evenly spaced spherical target volumes (2 cm radius) to completely fill it (N = 243) and organs-at-risk (OARs) were identified. Template trajectories were generated for six anatomical regions (frontal, medial, and posterior, with laterality dependence) based on previously published 4Ï€ optimization methods. VMAT treatment plans generated using anatomically informed template 4Ï€ trajectories and patient-specific 4Ï€ trajectories were compared against VMAT treatment plans generated with the standard four-arc template. To generate all trajectories, arc placement optimization was carried out by a previously published method, and a novel algorithm. Four comparisons to the standard VMAT trajectory template were made, by placing a spherical target in each of six anatomical regions of a test patient.
Results: Compared to standard VMAT, a trend of overall percentage reduction in maximum dose to OARs was seen using the previously published trajectory optimization method, with average values of -23Â±16% and -35Â±23% (N=6) for the anatomically informed template trajectories and patient-specific trajectories, respectively. A similar trend was observed using the novel algorithm for 4Ï€ trajectory optimization, with average maximum OAR percentage dose reductions of -13.1Â±21% and -50.1Â±23% for the anatomically informed template trajectories and patient-specific trajectories, respectively. Furthermore, both trajectory optimization techniques achieved conformity indices lower than the standard template (p<0.05).
Conclusion: Anatomically informed template trajectories may offer improved sparing to OAR relative to the standard VMAT template. In some cases, sparing improved further using trajectories generated from patient-specific 4Ï€ optimized trajectories.
Funding Support, Disclosures, and Conflict of Interest: The authors would like to acknowledge funding support from Brainlab AG, and the Atlantic Canada Opportunities Agency.