Trajectory optimization for dynamic couch rotation during volumetric modulated arc radiotherapy

Abstract

Abstract. Non-coplanar radiation beams are often used in three-dimensional conformal and intensity modulated radiotherapy to reduce dose to organs at risk (OAR) by geometric avoidance. In volumetric modulated arc radiotherapy (VMAT) non-coplanar geometries are generally achieved by applying patient couch rotations to single or multiple full or partial arcs. This paper presents a trajectory optimization method for a non-coplanar technique, dynamic couch rotation during VMAT (DCR-VMAT), which combines ray tracing with a graph search algorithm. Four clinical test cases (partial breast, brain, prostate only, and prostate and pelvic nodes) were used to evaluate the potential OAR sparing for trajectory optimized DCR-VMAT plans, compared with standard coplanar VMAT. In each case, ray tracing was performed and a cost map reflecting the number of OAR voxels intersected for each potential source position was generated. The least-cost path through the cost map, corresponding to an optimal DCR-VMAT trajectory, was determined using Dijkstra's algorithm. Results show that trajectory optimization can reduce dose to specified OARs for plans otherwise comparable to conventional coplanar VMAT techniques. For the partial breast case, the mean heart dose was reduced by 53%. In the brain case, the maximum lens doses were reduced by 61% (left) and 77% (right) and the globes by 37% (left) and 40% (right). Bowel mean dose was reduced by 15% in the prostate only case. For the prostate and pelvic nodes case, the bowel V 50Gy and V 60Gy were reduced by 9% and 45% respectively. Future work will involve further development of the algorithm and assessment of its performance over a larger number of cases in site specific cohorts.

Optimization approaches to volumetric modulated arc therapy planning

“…[46][47][48][49] Leaving potential issues regarding patient immobilization on a robotic couch aside, the first treatment planning studies investigating noncoplanar VMAT have reconfirmed a benefit of noncoplanar irradiation with regard to OAR sparing. 33,45,47,[50][51][52][53] From the mathematical and technical side, the optimization of an irradiation trajectory shares the known issues of beam angle optimization (BAO) for step&shoot IMRT. When viewed as a continuous optimization problem, BAO is highly nonconvex.…”

“…For the second step, all VMAT methods discussed in this paper can be applied with minor adjustments. The trajectories used for the above treatment planning studies were either found through inspection by a human planner, [50][51][52] using geometric heuristics, 45,53 or exhaustive search considering nine different couch tilts. 47 Wild et al 33 use a noncoplanar beam ensemble which was optimized with a genetic algorithm 49 for step&shoot IMRT to construct a noncoplanar VMAT trajectory.…”

A simple and robust trajectory‐based stereotactic radiosurgery treatment

“…In addition, they involved sporadic couch movements, which are both uncomfortable, can result in intra‐fraction motion and require complex quality assurance (QA) protocols. While previous methods successfully presented the dosimetric benefits of a trajectory‐based delivery, they did not systematically study the dosimetric benefits of trajectory modulation. It is therefore difficult to assess whether the dosimetric benefits of trajectory‐based deliveries were fully utilized by these methods.…”

Geometric Verification of Dynamic Wave Arc Delivery With the Vero System Using Orthogonal X-ray Fluoroscopic Imaging

“…Treatment planning studies went even further, exploring the possible benefits of VMAT delivery simultaneously with couch rotations (4)(5)(6). Other groups such as Yang et al (7) and Smyth et al (8) have additionally developed direct trajectory optimization methods to identify optimal 3D radiation delivery trajectories. All these studies share the same disadvantage in that the treatment couch needs to be changed during gantry rotation, which might introduce patient movement and potential collision.…”