Optimal delivery of DMLC Arc Therapy

摘要

Purpose: The continuous delivery of a specific treatment plan for an arc therapy can be achieved with multiple solutions for speed of gantry rotation, beam dose rate variation in time and with various speed trajectories of MLC leaves. This non-uniqueness of arc therapy delivery creates situations that given treatment plans can be delivered with arc with variable degrees of efficiency. The goal of this study is to find the most time efficient realization of the arc delivery provided all constraints of the delivery system are satisfied.Methods and Materials: The starting point for our considerations is that the specific plan of treatment has been derived for arc radiation therapy. We identify first the invariants of the arc therapy. These are parameters of the plan that have to be kept unchanged during delivery to preserve the integrity of the plan, i.e. they assure that plan delivered leads to dose distribution that is identical to dose distribution derived at the treatment planning process. We find that dose delivery invariants include file defining apertures of MLC as function of gantry angle and file defining beam intensity (MU) as function of gantry angle. The other point of our considerations exemplifies limitations of delivery systems for arc therapies. These constraints include gantry angular speed limit, beam dose rate limit and MLC leaf speed limits. Provided above invariants and limitations are satisfied, there exist multiple solutions for arc therapy delivery. We derive formula for such determination of gantry rotation speed, beam dose rate variation and MLC leaf speeds during delivery that lead to minimal time of arc therapy of a given plan.Results: We investigate the example of arc therapy comparing delivery performed under standard delivery algorithm (Varian Medical system) and our time optimized delivery. We first solve the optimization problem and define delivery files. We then simulate deliveries based on parameters derived from standard algorithms and from our solutions. In our preliminary study we find that both deliveries provide identical dose distributions and observe that our algorithm leads to 10-15% decrease in delivery time.Conclusions: Investigation of minimal delivery time arc radiation therapy demonstrates that the proposed method provides a viable option for continuous delivery of arc therapy treatments implemented with clinical TPS and clinical linear accelerators. The phantom study shows that minimal delivery time arc radiation therapy improves treatment efficiency without compromising dosimetric integrity of dose parameters at irradiation process.