Dosimetry Analysis Of Precise Radiotherapy Techniques For Pituitary Tumors

Background and objective:The purpose of this study is to compare the dosimetric differences among three dimensional conformal radiotherapy(3D-CRT),volumetric modulated arc therapy(VMAT),helical tomotherapy(TOMO)and X knife,then provide more accurate optimization for clinical treatment of patients with pituitary adenoma Methods:14 patients with pituitary adenoma in Peking Union Medical Hospital after standard of diagnosis and treatment were selected for this comparison.Plans of three field of 3D-CRT?VMAT?TOMO and X knife were developed on the same CT-MRI fusion image of each patient respectively.The dose-volume histograms(DVH)based parameters including conformal index(CI)and homogeneity index(HI),inhomogeneity coefficient(IC)of planning target volume(PTV)and the dose distribution on organs at risk(OAR)were evaluated.We also analyzed the monitor units(MU)and delivery time of different plans.For nonfunctioning pituitary adenoma,PTV in fractionated radiation therapy(FRT)was 3mm margin around gross tumor volume(GTV)while the prescription dose was 50.4 Gy in 28 fractions,and PTV of stereotactic radiosurgery was lmm margin around GTV while the margin dose was 14.10 Gy.For functioning pituitary adenomas,PTV of FRT is the volume of clinical target volume(CTV,preoperative tumor range)expanded by 3mm,the prescribed dose of PTV is 50.4 Gy,the prescribed dose of GTV is 60.2Gy in 28 fractions.According to whether the difference conforms to the normal standard,paired sample t test,Friedman test and Wilcoxon signed-rank test were respectively used for data analysis.P<0.05 was considered as statistically significant.Results:In patients with non-functioning pituitary microadenoma,the homogeneousness and conformal degree of FRT were better than that of X knife.X knife could not be implemented in the treatment planning of nonfunctioning pituitary macroadenomas,because the Dmax of OARs exceeded normal range.TOMO have similar CI and better HI with VMAT,and both are better than 3D-CRT.In patients with functioning pituitary adenoma,the TOMO program can achieve better PCTV coverage than VMAT,and the minimum dose of PCTV is closer to the prescribed dose,and the CI of GTV is closer to 1.In terms of the radiation dose of normal tissue,in the pituitary microadenoma,except for the high maximum dose of normal pituitary tissue,the X knife showed better sparing for OARs and normal tissue.The comparison between the three plans of FRT showed that the maximum dose of brainstem and temporal lobe in TOMO were lower than VNAT and 3D-CRT(P<0.05).In both TOMO and VMAT plans,the dose received by optic chiasma,normal pituitary tissue and pituitary stalk is lower than 3D-CRT,but there is no significant difference between them.The dose of the lateral optic nerve in the plan of VMAT is higher than that of 3D-CRT and TOMO,and the radiation dose of the same lateral optic nerve in the plan of TOMO is lower than that of VMAT and CRT.3D-CRT protected the lens and eyes better than VMAT and TOMO.As for the amount of MU and time of delivery,TOMO>VMAT>3D-CRT..Conclusion:SRS should be considered in the treatment of non-functioning pituitary microadenomas,while the homogeneousness and conformal degree is not that good,but it can significantly reduce the surrounding normal tissues by irradiation dose.TOMO plan can get better target conformal degree and homogeneousness in almost all cases,and at the same time further reduce the dose to normal tissue,which may help to reduce patients related adverse reaction.VMAT plan and TOMO have similar conformal fitness,but in the patients with functioning pituitary adenoma,GTV conformal fitness is poor,and the radiation dose to the lateral optic nerve is high.3D-CRT can reduce the dose of lens and eyes,but has no obvious advantage in other aspects.