Four‐dimensional dose evaluation using deformable image registration in radiotherapy for liver cancer

Purpose:In order to evaluate the dosimetric impact of respiratory motion on the dose delivered to the target volume and critical organs during free‐breathing radiotherapy, a four‐dimensional dose was evaluated using deformable image registration (DIR).Methods:Four‐dimensional computed tomography (4DCT) images were acquired for 11 patients who were treated for liver cancer. Internal target volume‐based treatment planning and dose calculation (3D dose) were performed using the end‐exhalation phase images. The four‐dimensional dose (4D dose) was calculated based on DIR of all phase images from 4DCT to the planned image. Dosimetric parameters from the 4D dose, were calculated and compared with those from the 3D dose.Results:There was no significant change of the dosimetric parameters for gross tumor volume (p > 0.05). The increase Dmean and generalized equivalent uniform dose (gEUD) for liver were by 3.1% ± 3.3% (p = 0.003) and 2.8% ± 3.3% (p = 0.008), respectively, and for duodenum, they were decreased by 15.7% ± 11.2% (p = 0.003) and 15.1% ± 11.0% (p = 0.003), respectively. The Dmax and gEUD for stomach was decreased by 5.3% ± 5.8% (p = 0.003) and 9.7% ± 8.7% (p = 0.003), respectively. The Dmax and gEUD for right kidney was decreased by 11.2% ± 16.2% (p = 0.003) and 14.9% ± 16.8% (p = 0.005), respectively. For left kidney, Dmax and gEUD were decreased by 11.4% ± 11.0% (p = 0.003) and 12.8% ± 12.1% (p = 0.005), respectively. The NTCP values for duodenum and stomach were decreased by 8.4% ± 5.8% (p = 0.003) and 17.2% ± 13.7% (p = 0.003), respectively.Conclusions:The four‐dimensional dose with a more realistic dose calculation accounting for respiratory motion revealed no significant difference in target coverage and potentially significant change in the physical and biological dosimetric parameters in normal organs during free‐breathing treatment.