Room: Karl Dean Ballroom A1
Purpose: In the context of radiotherapy, there are various presentations where dose delivery is challenging, particularly when the planning treatment volume (PTV) is adjacent to the organ at risk (OAR). In such scenarios, a trade-off exists whereby the dose constraints of the OARs must be considered in tandem with the coverage requirements of the PTV. This limitation can be mitigated by introducing a gantry static continuous couch motion (GsCMO) technique (1-2Â° increments). In this work, we will evaluate the feasibility of automatically implementing this approach.
Methods: Simulated arcs utilizing multiple static fields and sliding window intensity modulated radiotherapy (IMRT) GsCMO were applied in brain for a tumor situated between the optical chiasm and brainstem. Static fields were automatically merged using an in house developed MATLABÂ® script, producing a single xml file facilitating continuous delivery of the treatment plan within the TrueBeamÂ® Radiotherapy System developer mode. Treatment was delivered to an IMRT quality assurance phantom, scanned vertically to avoid beam entry at the edge of the phantom. Quantitative film analysis was also performed for qualitative field verification. Comparison of the simulated radiation dose vs. measured dose distributions was performed based on various metrics including 3% dose difference, 3mm distance to agreement and 2-dimensional gamma analysis.
Results: Comparisons of simulated arcs and measured dose distributions utilizing GsCMO yielded 97% passing score with median 2-dimensional gamma index of 0.356 and absolute median dose difference of 0.368Gy. Delivery time for simulated arcs was significantly shorter (<5min) as compared to individual fields (~30min).
Conclusion: Delivery of GsCMO to introduce dose modulation in brain and ensure coverage of the PTV while respecting the dose constraints of the OARs in brain using is achievable within the TrueBeamÂ® Radiotherapy System developer mode. Further advancement of this technique will enable dose calculation for GsCMO and implementation into clinical practice.