Purpose
Dose‐volume constraints (DVCs) continue to be common features in intensity‐modulated radiation therapy (IMRT) prescriptions, but they are non‐convex and difficult to incorporate. We propose computationally efficient methods to incorporate dose‐volume constraints (DVCs) into automated IMRT planning.
Methods
We propose a two‐phase approach: in phase‐1, we solve a convex approximation with DVCs. Although this convex approximation does not guarantee DVC satisfaction, it provides crucial initial information about voxels likely to receive doses below DVC thresholds. Subsequently, phase‐2 solves an optimization problem with maximum dose constraints imposed on those subthreshold voxels. We further categorize DVCs into hard‐ and soft‐DVCs, where hard‐DVCs are strictly enforced by the optimization and soft‐DVCs are encouraged in the objective function. We tested this approach in our automated treatment planning system which is based on hierarchical constrained optimization. Performance is demonstrated on a series of paraspinal, lung, oligometastasis, and prostate cases as well as a small paraspinal case for which we can computationally afford to obtain a ground‐truth by solving a non‐convex optimization problem.
Results
The proposed algorithm successfully meets all the hard‐DVCs while increasing the overall computational time of the baseline planning process (without DVCs) by 20%, 10%, and 11% for paraspinal, oligometastasis, and prostate cases, respectively. For a soft‐DVC applied to the lung case, the dose‐volume histogram curve moves toward the desired direction and the computational time is increased by 11%. For a low‐resolution paraspinal case, the ground‐truth solution process using mixed‐integer programming methods required 15 h while the proposed algorithm converges in only 2 min with a proximal solution.
Conclusions
A computationally tractable algorithm to handle hard‐ and soft‐DVCs is developed which is capable of satisfying DVCs without any parameter tweaking. Although the algorithm is demonstrated in our in‐house developed automated treatment planning system, it can potentially be used in any constrained optimization framework.