Abstract:

Objective

To study the differences of the clinical target volume (CTV)based on three-dimensional CT (3D-CT) and four-dimensional CT (4D-CT) of the whole breast after breast-conserving surgery.

Methods

Thirteen patients after breast-conserving surgery underwent 3D-CT simulation scans followed by 4D-CT simulation scans of the thorax during free breathing. During 4D-CT scanning, real-time position management (RPM)system simultaneously recorded the respiratory signals. The CT images with respiratory signal data were reconstructed and sorted into 10 phase groups in a respiratory cycle. Data sets for 3D-CT and 4D-CT scans were then transferred to Eclipse treatment planning software. The 4D-CT image of the end-inhalation phase (T0) served as a background and the other nine phases (T10,T20,T30…T90), maximum intensity projection (MIP) image and 3D-CT image were registered. The CTV were manually delineated on the registered images of the 3D-CT, T0, middle-exhalation (T20), end-exhalation (T50), MIP images based on the T0 of 4D-CT by a radiation oncologist at two different times. Then the CTV_3D, CTV₀, CTV₁₀…CTV_MIP were delineated and defined on the 3D-CT, T0, T10…MIP images based on the T0 images of 4D-CT by the same radiation oncologist. All the CTVs (CTV₀, CTV₁₀, CTV₁₀…CTV₉₀) delineated on the 10 phases of the 4D-CT images were fused into an internal clinical target volume (ICTV). The T0, T20, T50, MIP images were selected from the CTVs of the 4D-CT to compare with the 3D-CT image. The differences of the targets delineated on the same images by the same radiation oncologist at different times were compared. The volumes of the CTV_S, the matching index (MI) and the degree of inclusion (DI) were compared respectively.

Results

There was no difference in the CTV delineated by the same oncologist no matter based on 3D-CT or 4D-CT(P>0.050). The CTVs volumes of ten phases in 4D-CT were not impacted by respiratory movement(P>0.05). The median volume of CTV_3D,CTV₀,CTV₂₀, CTV₅₀, CTV_MIP were 708.11 cm³, 721.29 cm³, 725.04 cm³, 723.89 cm³,and 728.69 cm³, respectively. The volume demonstrated no significant difference between CTV_3D and CTV₀, CTV₂₀, CTV₅₀, CTV_MIP(P>0.050). The median MI of CTV_3Dand CTV₀,CTV₂₀, CTV₅₀ were 0.88, 0.86 and 0.86,respectively. the difference of the MI between CTV_3D and CTV₀, CTV₂₀, CTV₅₀ was not statistically significant (x²= 0.462, P = 0.794).The median DI of CTV₀, CTV₂₀, CTV₅₀in CTV_3D were 0.94,0.93 and 0.92, respectively.CTV_3Din CTV₀, CTV₂₀, CTV₅₀ were 0.95, 0.95 and 0.94, respectively. There was no significant difference between the DI of CTV_3D in CTV of the single phases of 4D-CT and the DI of CTV of the single phases in CTV_3D(P>0.05). The median ICTV was 793.56 cm³,larger than that of CTV_3D(Z=-3.180, P = 0.001)and the median MI between CTV_3D and ICTV was 0.86. The median DI of ICTV in CTV_3D and CTV_3Din ICTV were 0.91 and 0.96;the difference was significant(Z = -3.180, P = 0.001). ICTV was significantly higher than CTV_MIP(Z = -3.180, P = 0.001) and the DI between the two had a significant difference(Z = -3.180, P = 0.001). The median MI of ICTV and CTV_MIP was 0.93.

Conclusions

The delineation of clinical target volume of the whole breast would not be influenced by scan mode when the CTV is delineated by the same oncologist under the same delineation criterion. The 3D-CT shows limited movement information; the construction of internal target volume (ITV) is significantly impacted by respiratory movement. So ITV of whole breast target delineated on the 4D-CT images is more reasonable.

Key words: breast-conserving treatment, whole breast target, three-dimensional CT, four-dimensional CT, target delineation