A system for surgical procedure assistance, comprising: a total air volume estimation unit configured to obtain a first volume of air inside a lung based on a first image of the lung captured prior to a surgical procedure, wherein the lung has a first shape on the first image; an outflow air volume estimation unit configured to obtain a second volume of air deflated from the lung based on a second image of the lung captured during the surgical procedure; a deflation unit configured to estimate a second shape of the lung based on the first shape of the lung, the first air volume inside the lung, and the obtained second volume of air deflated from the lung by: calculating a third volume of air inside the lung during the surgical procedure based on the second volume, determining a ratio between the first volume and the third volume, for each voxel included in the first shape of the lung on the first image, estimating a first volume of air inside the voxel based on an intensity of the voxel, and calculating a second volume of air inside the voxel based on the first volume of air inside the voxel and the ratio, and condensing voxels along a gravity direction based on the second volume of air inside the voxels; and a pre-operative plan transformation unit configured to update a surgical plan based on the estimated second shape of the lung. a total air volume estimation unit configured to obtain a first volume of air inside a lung based on a first image of the lung captured prior to a surgical procedure, wherein the lung has a first shape on the first image; an outflow air volume estimation unit configured to obtain a second volume of air deflated from the lung based on a second image of the lung captured during the surgical procedure; a deflation unit configured to estimate a second shape of the lung based on the first shape of the lung, the first air volume inside the lung, and the obtained second volume of air deflated from the lung by: calculating a third volume of air inside the lung during the surgical procedure based on the second volume, determining a ratio between the first volume and the third volume, for each voxel included in the first shape of the lung on the first image, estimating a first volume of air inside the voxel based on an intensity of the voxel, and calculating a second volume of air inside the voxel based on the first volume of air inside the voxel and the ratio, and condensing voxels along a gravity direction based on the second volume of air inside the voxels; and a pre-operative plan transformation unit configured to update a surgical plan based on the estimated second shape of the lung. calculating a third volume of air inside the lung during the surgical procedure based on the second volume, determining a ratio between the first volume and the third volume, for each voxel included in the first shape of the lung on the first image, estimating a first volume of air inside the voxel based on an intensity of the voxel, and calculating a second volume of air inside the voxel based on the first volume of air inside the voxel and the ratio, and condensing voxels along a gravity direction based on the second volume of air inside the voxels; and a pre-operative plan transformation unit configured to update a surgical plan based on the estimated second shape of the lung. <EOS>