Four-dimensional intensity-modulated radiotherapy planning for dynamic multileaf collimator tracking radiotherapy.

摘要

PURPOSE: To develop a four-dimensional intensity-modulated radiotherapy (IMRT) planning method for dynamic multileaf collimator (DMLC)-based tumor tracking that takes respiratory motion into consideration. METHODS AND MATERIALS: Using the concept of optimal deformation, a series of apertures are placed at different phases in the same segment to ensure maximally similar dose contributions at various anatomic points. We used a direct aperture optimization method to find a set of segments that achieved an optimal dose distribution for aperture shapes at the reference phase and achieved corresponding optimal deformations at other phases that took respiratory motion into consideration. In our four-dimensional direct aperture optimization (4D-DAO) method, a simulated annealing algorithm and a conjugate gradients algorithm were used to optimize the shape of the segments and the monitor units, respectively. We then compared the optimization results for three-dimensional conformal radiotherapy and 4D-DAO based on a set of simulated respiration 4D computed tomography (4DCT) data and a set of real 4DCT data. RESULTS: Dosimetric analysis indicated that, compared with the 3DCRT method, the dose distribution is significantly improved when the optimal deformation tracking technique is used, even when the maximum velocity limit of the DMLC leaves is set. CONCLUSIONS: The proposed 4D-IMRT planning method can find a set of segments and the corresponding leaf movements, which can trace the tumor motion and thus protect more normal tissue from radiation.