Objective:To systematically evaluate the differences in CT values between virtual non-contrast (VNC) images and true non-contrast (TNC) images generated from dual-energy CT (DECT), and to validate the feasibility of VNC images replacing TNC images in dose calculations for photon and proton radiotherapy plans.Methods:A retrospective analysis was conducted on the imaging data of 40 patients with solid tumors (20 cranial, 10 thoracic and 10 abdominal cases) who underwent DECT scans at Cancer Hospital of Shandong First Medical University from February 2022 to May 2023. VNC and TNC images were registered slice-by-slice. The differences in CT values of anatomical structures were compared, and Pearson correlation analysis was used to evaluate the correlation of CT values of different anatomical structures in VNC and TNC images. For structures with significant differences, linear regression models (TNC=β×VNC+α) were established using the least squares method. In the Varian Eclipse 15.5 treatment planning system, photon and proton radiotherapy plans based on TNC images and VNC images, as well as the proton radiotherapy plan based on the VNC images corrected by the regression models, were respectively designed. Dose differences of radiotherapy plans designed based on the two images were evaluated. To evaluate dose variations in regions adjacent to the clinical target volume (CTV), two 2-mm-thick annular reference structures were generated on the axial slice containing the largest cross-section of the CTV, extending cranially and caudally from the CTV. These structures were designated as Ring_p and Ring_d, respectively.Results:The differences in CT values between VNC and TNC images were mainly concentrated in the bony structure. The CT values difference between TNC and VNC images was (409.07±53.38) HU for the skull in 20 cranial tumor patients ( t=13.88, P<0.001), and (118.66±20.90) HU for the vertebral bone in 10 thoracic and 10 abdominal tumor patients ( t=10.43, P<0.001). The CT values of the skull and spine showed high correlation between TNC and VNC images ( r=0.98, P<0.001; r=0.99, P<0.001). The regression models established respectively were: TNC=1.859×VNC+33.896 (skull), and TNC=1.827×VNC+5.491 (spine). For photon radiotherapy plans based on TNC and VNC images, the D mean of the CTV were (60.00±0.00) and (60.00±0.00) Gy respectively, with D mean of Ring_p were (61.17±1.69) and (61.01±1.67) Gy, and Ring_d were (55.26±2.06) and (55.20±1.94) Gy, respectively. The relative dose differences in D mean between the two image types were 0 ( t<0.01, P>0.999), 0.33% ( t=0.30, P=0.766), and 0.19% ( t=0.07, P=0.947), all with no statistically significant differences. For proton radiotherapy plans based on TNC and VNC images, the D mean of the CTV were (61.73±0.32) and (61.67±0.26) Gy (RBE), respectively, with D mean of Ring_p were (61.19±0.44) and (60.53±1.22) Gy (RBE), and Ring_d were (60.97±0.67) and (59.80±4.26) Gy (RBE), respectively. The relative dose differences in D mean between the two image types were 0.24% ( t=0.63, P=0.530), 1.80% ( t=1.45, P=0.156), and 3.56% ( t=2.26, P=0.030), with a statistically significant difference in the Ring_d region. In the proton radiotherapy plan designed based on the corrected VNC images, the D mean of the CTV was (61.75±0.32) Gy (RBE), Ring_p was (61.43±0.71) Gy (RBE), and Ring_d was (59.96±2.80) Gy (RBE). The relative dose differences in D mean between TNC images and corrected VNC images were 0.16% ( t=0.19, P=0.850), 0.76% ( t=1.32, P=0.196), and 2.22% ( t=1.93, P=0.061), respectively, with no statistically significant differences. Conclusions:The differences in CT values between VNC and TNC images in DECT mainly exist in bony structures, particularly in the skull and vertebrae. For patients with cranial tumors, VNC images can be directly used in photon radiotherapy planning. In contrast, for proton therapy, after being corrected by the regression model, VNC images can effectively replace TNC images for the dose calculations of radiotherapy plan.

Objective:To establish the normal reference value of lumbar bone mineral density (BMD) under quantitative CT (QCT) in Chinese healthy adult females and to explore the regional differences.Methods:Total of 35 431 healthy women who met the inclusion criteria of Chinese health quantitative CT big data program were selected in this study. The BMD of the central plane of L 1 and L 2 vertebrae was measured by Mindways′s QCT system, and the mean value was taken. One-way analysis of variance was used to compare the BMD differences of lumbar vertebrae in women of different ages and regions. The subjects were grouped by an age interval of 10 years, and the level of BMD in different regions of the same age group were compaired. Results:The peak BMD of Chinese healthy adult women appeared in the age group of 20-29 years (Northeast China(183.01±24.58) mg/cm 3, North China (188.93±24.80) mg/cm 3, East China (187.54±27.71) mg/cm 3, South China (186.22±33.72) mg/cm 3, Central China (176.33±24.91) mg/cm 3, Southwest China(182.25±28.00) mg/cm 3), and then it decreased with age. The level of BMD in different regions decreased with the age. Before the age of 70 years, BMD in Central and Southwest China was always at a low level((176.23±24.91) to (90.38±28.12) mg/cm 3, 182.25±28.00 to (88.55±25.68) mg/cm 3), lower than those in Northeast China ((183.01±24.58) to (99.69±27.85) mg/cm 3), North China ((188.93±24.80) to (95.89±26.12) mg/cm 3), East China ((187.54±27.71) to (95.65±27.86) mg/cm 3). After 70 years of age, BMD tended to be the same in different regions ( P>0.05). The BMD values in Central China and Southwest China were similar in the age group of 40-60 years ( P>0.05). The BMD values in the health adult femles in the age group of 60 years in different regions of Chinawere all lower than those of bone mass abnormality (all P<0.05). The detection rate of osteoporosis in females over 50 years was the highest in Southwest China (25.65%) and it was the lowest in North China (17.30%). Conclusions:This study establishes reference values of BMD under QCT in healthy Chinese women, which can be used as a reference basis for identifying women with low BMD who are at risk of osteoporosis. The BMD value is the lowest in Southwest China and the highest in South China.