Objective To develop a novel method for measuring the Hounsfield Unit(HU)value of the surface carbon fiber material of the Varian Exact IGRT Couch,and to establish a treatment couch model in the treatment planning system(TPS)for correcting the attenuation of radiation dose caused by the treatment couch.Methods Two different field combinations were used to measure the radiation dose attenuation at the thin end and the middle medium-thickness part of the Varian Exact IGRT Couch.Dose deviations were measured when radiation passed through the treatment couch or not.Multiple sets of different HU values for the couch surface materials were defined in the TPS,and the dose difference between with and without couch was calculated under the same conditions as the measurements.The HU value of the treatment couch material corresponding to the actual measurements was found by data comparison and analysis.Results The attenuation for two interpenetrating fields was-2.49%to-1.69%at the thin end,and-3.43%to-2.23%at the medium-thickness part.The attenuation for multiple oblique incident fields ranged from-3.12%to-2.17%at the thin end,and that was-3.59%to-2.86%at the medium-thickness part.When the HU values of the couch model's surface and internal materials in the TPS were defined as-500 and-960,for two interpenetrating fields,the attenuation was-2.57%to-1.53%at the thin end,and-3.28%to-2.18%at the medium-thickness part;while for multiple oblique incident fields,the attenuation was-3.12%to-2.21%at the thin ends,and-3.42%to-2.43%at the medium-thickness part.These calculated results were consistent with the actual measurement values.For 40 verification plans,the average point dose difference between measurement and calculation in TPS were 0.90%and 0.89%at the thin end and medium-thickness part,respectively.Conclusion This novel measurement method can measure the HU value of the surface carbon fiber material and internal foam material of Exact IGRT Couch.Defining the HU values of these two materials of the couch model in the TPS as-500 and-960 can correct the radiation dose attenuation caused by the treatment couch,thereby improving the dose accuracy of the target volume and organs-at-risk.

Objective To develop a novel method for measuring the Hounsfield Unit(HU)value of the surface carbon fiber material of the Varian Exact IGRT Couch,and to establish a treatment couch model in the treatment planning system(TPS)for correcting the attenuation of radiation dose caused by the treatment couch.Methods Two different field combinations were used to measure the radiation dose attenuation at the thin end and the middle medium-thickness part of the Varian Exact IGRT Couch.Dose deviations were measured when radiation passed through the treatment couch or not.Multiple sets of different HU values for the couch surface materials were defined in the TPS,and the dose difference between with and without couch was calculated under the same conditions as the measurements.The HU value of the treatment couch material corresponding to the actual measurements was found by data comparison and analysis.Results The attenuation for two interpenetrating fields was-2.49%to-1.69%at the thin end,and-3.43%to-2.23%at the medium-thickness part.The attenuation for multiple oblique incident fields ranged from-3.12%to-2.17%at the thin end,and that was-3.59%to-2.86%at the medium-thickness part.When the HU values of the couch model's surface and internal materials in the TPS were defined as-500 and-960,for two interpenetrating fields,the attenuation was-2.57%to-1.53%at the thin end,and-3.28%to-2.18%at the medium-thickness part;while for multiple oblique incident fields,the attenuation was-3.12%to-2.21%at the thin ends,and-3.42%to-2.43%at the medium-thickness part.These calculated results were consistent with the actual measurement values.For 40 verification plans,the average point dose difference between measurement and calculation in TPS were 0.90%and 0.89%at the thin end and medium-thickness part,respectively.Conclusion This novel measurement method can measure the HU value of the surface carbon fiber material and internal foam material of Exact IGRT Couch.Defining the HU values of these two materials of the couch model in the TPS as-500 and-960 can correct the radiation dose attenuation caused by the treatment couch,thereby improving the dose accuracy of the target volume and organs-at-risk.

Objective To evaluate the diagnostic value of MSCT angiography and postprocessing techniques in the diagnosis of spontaneous isolated dissection of superior mesenteric artery(SIDSMA).Methods Twenty patients with SIDSMA performed with MSCT angiography were analyzed retrospectively.The volume data were transferred to the workstation for image postprocessing and performed with various postprocessing techniques such as multi-planar reconstruction(MPR),curved planar reconstruction(CPR), volume rendering(VR)and maximum intensity projection(MIP).Results The dissection length of SIDSMA was positively correlated with visual analogue scale(VAS).MPR,CPR and VR clearly showed the intimal flap,true and false lumen.MPR and CPR displayed more entries of dissection than VR.VR demonstrated the extension of the involved aorta and its branches,but cannot satisfactorily demonstrate the entry of SIDSMA.Conclusion MSCT angiography is of positive applicable value to the diagnosis of SIDSMA.MPR, CPR and VR may be optimal choice as post processing techniques for diagnosis of SIDSMA.