| Objective:In the course of tumor radiotherapy,breathing movement,image scanning,postural fixation,tumor size and number are always important factors affecting the accurate treatment of tumor.For chest tumors that are small in size or located in the lower lobe of the lung,respiratory exercise has the greatest effect on therapeutic efficacy.In the traditional sense,radiotherapists include respiratory motion amplitude according to the experience of external expansion of the target area,but when the external expansion is small,the phenomenon of missing the target or even missing the target will occur.When the external expansion is excessive,it is inevitable that the normal tissue is exposed to a high dose,which will cause serious adverse reactions to the prognosis of patients.Therefore,in this study,when stereotactic body radiotherapy(SBRT)was performed on patients with primary or metastatic lung cancer,4D-CT combined with respiratory gating technology was used for pre-radiotherapy scanning,and respiratory gating plan and conventional radiotherapy plan were designed.By comparing the target size,dosimetry differences,adverse radiotherapy reactions and clinical efficacy of the two groups of plans,To evaluate the feasibility of 4D-CT combined with respiratory gating technique in stereotactic body radiotherapy for lung cancer.Methods:A total of 39 patients with primary or metastatic lung cancer(58 lesions)treated in the Radiotherapy Center of the Affiliated Hospital of Yangzhou University from June 2019 to September 2022 were collected.The CT data sets of the patients were processed by 4D-CT combined with respiratory gated image scanning,and a total of 10 groups of CT images were obtained by 4D software program.After importing 10 sets of CT images with respiratory phase into the workstation of Varian Eclipse 15.5 system,the radiotherapist sketched GTV on the 10 sets of images,and then merged the 10 sets of images into the perfect time images to obtain the ITV1 of the conventional radiotherapy plan,and PTV1 was formed through the external expansion of a certain range.It is used to simulate CT images under conventional radiotherapy.5～6 groups of images with less respiratory amplitude were selected and fused to obtain ITV2,which was expanded to form PTV2 within a certain range,thus forming respiratory gated images.Respiratory gated plan and conventional radiotherapy plan were designed for each patient.SBRT was applied to all patients,and 6MV-X irradiation PTV was planned,with a total radiotherapy dose of 60Gy/8F.The volume and dose of target areas and organs at risk outlined by the two groups were compared,and the adverse reactions and efficacy of radiotherapy were followed up within 6 months after the end of treatment.Results:(1)Compared with the conventional plan,the volume of ITV and PTV under the respiratory gated plan was smaller.The average volume of ITV in 58 lesions was(8.3±7.9)cm~3 and(12.4±12.1)cm~3,respectively,and the average volume of PTV was(21.5±17.7)cm~3 and(28.8±23.7)cm~3,respectively.The difference was statistically significant(P<0.001).Thirteen patients had multiple lung metastases,with a total of 32 lesions.The average volume of ITV was(6.0±6.2)cm~3 and(9.1±9.9)cm~3,respectively,and the average volume of PTV was(15.9±15.1)cm~3 and(21.8±21.5)cm~3,respectively,with statistically significant differences(P<0.001).(2)The dose(D95)of 95%PTV in gated plan and conventional radiotherapy plan was(6 063.5±100.6)cGy and(6 014.2±101.6)cGy,respectively,and the difference was statistically significant(P=0.007).However,the mean dose,minimum dose,maximum dose,5%dose received by PTV and 50%dose received by PTV of the two groups had no significant statistical significance.The target conformal indexes of the two groups were(0.8±0.05)and(0.7±0.08),respectively,and the difference was statistically significant(P=0.005).For multiple lung lesions,the dosage of 95%PTV received by gated plan and conventional radiotherapy plan was(6 063.5±100.6)cGy and(6014.2±101.6)cGy,respectively,and the difference was statistically significant(P=0.003).(3)The volume percentage of normal lung tissue receiving radiation dose higher than 20Gy were(6.3±4.5)%and(7.4±4.8)%,respectively,and the difference was statistically significant(P=0.009).The percentage of volume receiving radiation dose higher than 5Gy was(19.2±11.1)%and(22.5±11.4)%,respectively,and the difference was statistically significant(P=0.009).The average dose received by both lungs under the gated plan was(403.5±230.2)cGy,which was significantly lower than the average dose received by the conventional plan(506.1±249.4)cGy,and the difference was statistically significant(P<0.001).The dose of 1cm~3 spinal volume received by the two groups was(1 165.4±960.4)cGy and(1 372.3±1023.4)cGy,respectively,with statistical significance(P=0.02);At the same time,the average cardiac dose under the gated plan was(247.2±262.1)cGy,which was significantly lower than that under the conventional plan(360.1±378.1)cGy,the difference was statistically significant(P=0.01).The incidence of radiation pneumonia was 32.4%and the local control rate was 81.1%.Conclusion:Compared with conventional radiotherapy plan,4D-CT combined with respiratory gating technique has definite efficacy in the treatment of primary and metastatic lung tumors,especially for patients with multiple lung metastases.It can accurately track the location of multiple tumors,significantly improve target volume and target dose,improve local control rate,and further reduce the dose of surrounding normal tissue while ensuring the target dose. |
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