Room: Exhibit Hall | Forum 7
Purpose: Dynamic conformal arc therapy (DCAT) in the Monaco treatment planning system (Elekta, Crawley, UK) allows optimization using varying dose rate and aperture modulation. The optimization efficiency of the Monte Carlo engine, plan quality, and delivery efficiency of DCAT plans were characterized along with target complexity for patients receiving stereotactic ablative radiotherapy (SABR) with breath-hold.
Methods: 18 patients were evaluated for SABR, and eight patients were planned with breath-hold to compare DCAT and VMAT techniques in Monaco. The complexity of the treatment plan associated with target and surrounding organs-at-risk (OARs) characteristics were defined. Total planning time associated with optimization efficiency (3 mm voxel size, 1% statistical uncertainty) for DCAT was recorded by an experienced dosimetrist and compared with VMAT. The plan quality of DCAT and VMAT to achieve RTOG/institutional criteria was evaluated in terms of resulting MU and modulation degree. The efficiency of the beam delivery was evaluated during breath-hold treatment.
Results: The median PTV was 31.2 cmÂ³ (range 5.5-128.0 cmÂ³). Most DCAT plans met RTOG/institutional criteria and were comparable to VMAT plans without degradation of plan quality in terms of target coverage and OARs dose. DCAT planning time to achieve the plan criteria was 1.7 times faster for simple cases (PTV>13 cmÂ³ and no surrounding OARs), but 1.5 times slower for complex cases (PTV>6 cmÂ³ and overlapping OARs or located <1mm, re-irradiation). The DCAT plans were optimized using on average -25% MUs, which resulted in, on average, 1.4 modulation degree versus 2.1 for VMAT plans. Beam delivery of the DCAT plan was faster than for VMAT plan, requiring 4-5 breath-holds versus 6-7 for VMAT.
Conclusion: DCAT planning is a highly efficient technique for patients receiving breath-hold SABR treatment with no loss in plan quality along with fewer MUs, limited MLC modulation, faster calculation, and delivery times for simple cases.