| PurposeBy using 4d-ct and its reconstruction technology,the planned tumor target area(PTV)was determined,and compared with the geometry and dosimetry of traditional 3d-ct in target delineation and intensity-modulated radiotherapy planning,so as to analyze its advantages and discuss the significance of 4d-ct in clinical application.MethodsFrom January 2017 to December 2018,radiotherapy department in our hospital were collected 10 cases of lung cancer patients,including 2cases of squamous carcinoma,4 cases of adenocarcinoma,3 cases of small cell carcinoma and undifferentiated carcinoma in 1 case,4 cases were male,female 6 cases,has a history of smoking in 5 cases,no smoking history in 5 cases,mild restrictive ventilatory dysfunction in 1case,moderate restrictive ventilatory dysfunction in 1 case and peripheral lung cancer 7 cases,the central type lung cancer in 3 patients.Respectively for the 10 patients with traditional 3 d-CT(three-phase breathing)and 4 d-CT positioning,respectively in 3 d-CT localization image sketch GTV1(quiet breathing),GTV2(at the end of the suction),GTV3(out)at the end,will GTV1,GTV2,into IGTV3 D GTV3 fusion,such as IGTV3 D outward expansion of 0.6 cm(squamous carcinoma)/0.8 cm(gland carcinoma,small cell carcinoma)generated CTV3 Dt,will CTV3 Dt + involvement of mediastinal lymph node areas such as outwardexpansion of 0.5 cm(placement error),generate PTV3 D.And delineate the organs at risk,including the lungs,spinal cord,and heart.The maximum density projection MIP and average density projection AIP were established on the 4d-ct positioning image,and the GTV was outlined under the MIP and marked as GTV4 D.CTV4Dt was generated by outward expansion of GTV4D(squamous cell carcinoma)/0.8cm(adenocarcinoma,small cell carcinoma),and PTV4 D was generated by outward expansion of CTV4Dt+ affected mediastinal lymph node region by 0.5cm(positioning error).The organs at risk were outlined on the AIP,including the lungs,spinal cord,and heart.For each patient,respectively designed two sets of radiotherapy plan: named 3 d-CT and 4 d-CT plan,plans to use 3 d coplanar more wild illuminate,in guarantee lesions and endanger organ under the premise of all conform to the requirements of the dose limit,plans for each of the two groups of patients with the same quantity and same direction of the radiation field,compare two sets of plans in target areas and organs of the geometry and threatening dosimetry difference.SPSS 21.0 was used for statistical analysis,and the analysis results were expressed as x s.Paired sample t test was used for comparison between groups,and P < 0.05 was considered statistically significant.ResultsAmong the 10 patients,the mean PTV3 D target volume was342.63±129.68cm3,and the mean PTV4 D target volume was280.28±135.96cm3,the difference was statistically significant(P < 0.05),indicating that the PTV volume generated by the fusion of the target area delineated under the MIP reconstructed by 4D-CT was smaller than that of the traditional 3D-CT.The mean value of V20(3D)in both lungs was0.2183±0.046,and the mean value of V20(4D)in both lungs was0.2005±0.056,and the difference was statistically significant(P<0.05).The mean value of V30(3D)in both lungs was 0.1377±0.0489,and the mean value of V30(4D)in both lungs was 0.1241±0.051,and the difference was statistically significant(P<0.05).The mean value of double-lung V40(3D)was 0.086 0.0363,and the mean value of double-lung V40(4D)was 0.0728 ±0.0402,and the difference was statistically significant(P<0.05).The mean value of double-lung MLD(3D)was 11.883±3.892 Gy,and the mean value of double-lung MLD(4D)was 10.605±4.103 Gy,and the difference was statistically significant(P<0.05).It indicates that the dose of normal lung tissue in the4D-CT program is less than that in the 3D-CT program.The mean cardiac V30(3D)was 0.1783(0.1125,0.3162),and the mean cardiac V30(4D)was0.1782(0.1244,0.3107).The difference was not statistically significant(P > 0.05).The mean value of cardiac V40(3D)was 0.0965±0.0408,and the mean value of cardiac V40(4D)was 0.0982± 0.0408,the difference was not statistically significant(P > 0.05).It indicates that the 4D-CT program has no significant advantage over the 3D-CT in terms of cardiac dose limitation.The mean value of spinal cord Dmax(3D)was22.596±13.282 Gy,and the mean value of spinal cord Dmax(4D)was20.612±13.022 Gy.The difference was statistically significant(P<0.05),indicating that the maximum dose received by the spinal cord in the4D-CT program was less than that in the 3D-CTprogram.ConclusionCompared with traditional 3D-CT,4D-CT technology can reduce the volume of planned tumor target area(PTV)and thereby reduce the dose to surrounding normal tissues,thus reducing the incidence of radioactivedamage to a greater extent.The target area was delineated on 4d-ct and its maximum density projection(MIP)after reconstruction,so that the motion trajectory of lung tumor could be described to the greatest extent,which not only reduced the leakage of target area,but also reduced the workload of clinicians. |
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