Dynamic Modulated Arc Therapy (DMAT): A Time Aware, Modulation Steered Optimization Framework for Next Generation Radiotherapy Delivery
Background: Conventional VMAT optimization treats delivery time and deliverability as emergent properties of control-point-centric models that ignore finite acceleration and other dynamic limits. As linacs gain axis speed and dose rate, the plan quality-time trade-off must become explicit and steerable. Purpose: To introduce Dynamic Modulated Arc Therapy (DMAT), a time-aware, modulation-steered framework that jointly optimizes dosimetric quality, delivery time, and modulation complexity. Methods: DMAT couples direct machine emulation (axis synchronization, finite acceleration), dynamic modulation control, and clinical metrics used directly as cost functions. A user-selected modulation level (-3 to +3) governs leaf-travel allowance, total MU, aperture complexity, and control-point (CP) density. Plans are generated by progressive-resolution optimization alternating dosimetric with sequencing/deliverability updates, with non-uniform CP redistribution and complexity-reducing post-processing. DMAT was evaluated on head-and-neck, lung SBRT, and prostate SBRT cases using a hypothetical accelerated system (2.5 RPM gantry, 6.25 cm/s MLC, 3000 MU/min). Results: Increasing modulation level raised modulation surrogates (MU/Gy, aperture complexity) and delivery time, with additional CPs concentrated in arc sectors where finer angular resolution was most beneficial. The trade-off was site dependent: head-and-neck gained substantial plan quality, whereas prostate and lung SBRT gained little beyond baseline. Negative levels predictably shortened delivery time at a fixed CP budget, with quantifiable quality loss. Conclusions: DMAT co-optimizes plan quality and modulation complexity under machine-aware timing and explicit user control, making quality-time trade-offs transparent and navigable and supporting time-constrained workflows such as motion management and adaptive radiotherapy.