Analysis And Comparison Of 3D-CRT And IMRT Dosimetry Of The Temporary Tissue Expander In Postmastectomy Radiation Therapy

PurposeThrough the comparison of the homogeneity and conformal index of dose distribution and coverage in the target area,and the exposure dose and volume of the organ at risk between IMRT and 3D-CRT of the temporary tissue expander in postmastectomy,this trial is to evaluate the dosimetric differences between IMRT plan and 3D-CRT plan,as well as between the delineation method of the total expander and the delineation method of only covering the posterior margin of pectoralis major muscle.MethodSeven cases of the temporary tissue expander in postmastectomy were seleceted from Suzhou for breast bracket position fixation、CT scan(layer thickness 5mm)and target delineation in radiotherapy,respectively.Take the chest wall and high-risk lymphatic drainage area as CTV.In this trial we uses two kinds of delineation methods to define CTV.CTV1 contains upper and lower lymphatic drainage area of the clavicle,CTV2 only contains the chest wall that conjugation of temporary tissue expanders and posterior margin of pectoralis major muscle,CTV3 covers the all chest wall of the temporary tissue expander.Meanwhile,delineate the images of organs at risk layer by layer.Images are transmitted into the Monaco and Eclipse three-dimensional treatment planning system(TPS).We made two 3D-CRT plans and two IMRT plans for each patient.Through the analysis of dose volume histogram(DVH)of all plans,the comparison could be made in the homogeneity and conformal index of dose distribution and coverage in the target area,as well as the exposure dose and volume of the organ at risk to analyse the merits and demerits of each plan.Results1.Regardless of the method of delineation,in conformal index(CI)of PTV,the IMRT plan had obvious advantages compared to the 3D-CRT plan(P>0.05),in the IMRT plan,the delineation method of the total expander was superior to the delineation method of only covering the posterior margin of pectoralis major muscle with statistical significance(P<0.05)in terms of CI;in the 3D-CRT plan,there was no significant difference in HI between the two methods of delineation(P>0.05);regardless of the method of delineation,in homogenous index(HI)of PTV,the IMRT plan had obvious advantages compared to the 3D-CRT plan(P < 0.05),in the IMRT plan or the 3D-CRT plan,the delineation method of the total expander was superior to the delineation method of only covering the posterior margin of pectoralis major muscle,there was significant difference in the IMRT plan only(P<0.05).For the comparison of maximum dose within CTV,in the delineation method of only covering the posterior margin of pectoralis major muscle,the IMRT plan was more than the 3D-CRT plan with statistical significance(P<0.05),in the IMRT plan or the 3D-CRT plan,the delineation method of the total expander was more than the delineation method of only covering the posterior margin of pectoralis major muscle with no statistical significance(P>0.05).For the comparison of mean dose within CTV,in the delineation method of only covering the posterior margin of pectoralis major muscle,the IMRT plan was more than the 3D-CRT plan with statistical significance(P<0.05),in the IMRT plan,the delineation method of the total expander was more than the delineation method of only covering the posterior margin of pectoralis major muscle with statistical significance(P<0.05).For the comparison of minimal dose within CTV,in the 3D-CRT plan,the delineation method of the total expander was more than the delineation method of only covering the posterior margin of pectoralis major muscle with statistical significance(P<0.05).2.For the protection of organs at risk heart,in the delineation method of only covering the posterior margin of pectoralis major muscle or in the delineation method of the total expander,for comparison of mean dose within heart、max dose within heart、V20、V25、V30 and V40,the IMRT plan had obvious advantages compared to the 3D-CRT plan,only V20 and V30 with statistical significance(P<0.05);in the IMRT plan,for comparison of max dose within heart、V5、V10、V20、V25、V30 and V40,the delineation method of only covering the posterior margin of pectoralis major muscle was superior to the delineation method of the total expander,only V40 with statistical significance(P<0.05);in the 3D-CRT plan,for comparison of all parameters,the delineation method of only covering the posterior margin of pectoralis major muscle was superior to the delineation method of the total expander,only mean dose within heart、V5 and V40 with statistical significance(P<0.05).For the protection of organs at risk coronary artery,in the delineation method of only covering the posterior margin of pectoralis major muscle,for comparison of mean dose within coronary artery、max dose within coronary artery、V20、V25 and V30,the IMRT plan had obvious advantages compared to the 3D-CRT plan,only mean dose within coronary artery with statistical significance(P<0.05);for comparison of V5 and V10,the 3D-CRT plan had obvious advantages compared to the IMRT plan,only V5 with statistical significance(P<0.05);in the delineation method of the total expander,for comparison of mean dose within coronary artery、max dose within coronary artery、V10、V20、V25 and V30,the IMRT plan had obvious advantages compared to the 3D-CRT plan,for comparison of V5,the 3D-CRT plan had obvious advantages compared to the IMRT plan,in the IMRT plan,for comparison of mean dose within coronary artery、max dose within coronary artery、V5、V20、V25 and V30,the delineation method of only covering the posterior margin of pectoralis major muscle was superior to the delineation method of the total expander;in the 3D-CRT plan,for comparison of all parameters,the delineation method of only covering the posterior margin of pectoralis major muscle was superior to the delineation method of the total expander,only V10 with statistical significance(P<0.05).For the protection of organs at risk ipsilateral lung,regardless of the method of delineation,for comparison of all parameters,the IMRT plan had obvious advantages compared to the 3D-CRT plan with statistical significance(P<0.05);in the 3D-CRT plan or the IMRT plan,for comparison of all parameters,the delineation method of only covering the posterior margin of pectoralis major muscle was superior to the delineation method of the total expander.For the protection of organs at risk trachea、thyroid gland and ipsilateral humeral head,the IMRT plan had obvious advantages compared to the 3D-CRT plan,the delineation method of only covering the posterior margin of pectoralis major muscle was superior to the delineation method of the total expander.Conclusion1.The Radiation Therapy for the temporary tissue expander in postmastectomy,IMRT enjoy more advantages than 3D-CRT in target area CI and HI,the delineation method of the total expander was superior to the delineation method of only covering the posterior margin of the pectoralis major muscle in terms of CI and HI.2.For the protection of organs at risk,such as heart and coronary artery,the IMRT plan compared with the 3D-CRT plan,better in high-dose irradiation and worse in low-dose irradiation;the delineation method of only covering the posterior margin of the pectoralis major muscle was superior to the delineation method of the total expander;for the protection of organs at risk,such as ipsilateral lung、trachea、thyroid gland and ipsilateral humeral head,IMRT had better protection than 3D-CRT,the delineation method of only covering the posterior margin of the pectoralis major muscle was superior to the delineation method of the total expander.3.Regardless of the method of delineation,there was no significant difference for MU value.