OBJECTIVETo increase the accuracy of beam targeting and improve the dose distributions in radiotherapy using a robust image registration algorithm based on control volumes.

METHODSControl volume mapping and thin-plate spline deformable transformation were combined. The use of the control volumes increased the accuracy for the deformable registration. A bi-directional mapping method was also employed to correctly match the control volumes.

RESULTSThe clinical images were simulated using the proposed two-step image registration algorithm. The simulation results indicated that the registration algorithm was robust and universal, even in cases of obvious deformation.

CONCLUSIONSThe algorithm provides a more convenient and robust resolution as compared to manual landmark-based methods and single-step deformable transformations, and may help in automatic image registration in radiation therapy.