Comparative Dosimetric Study Of Three Radiotherapy Strategics In Nasopharyngeal Carcinoma

Objective To compare the dosimetric advangtages and disadvantages of 2-dimensional radiotherapy(2DRT),2-dimensionalradiotherapy plus 3-dimensional conformal radiotherapy boost(2DRT+3D Boost)and intensity modulated radiotherapy(IMRT)plans for patients firstly with nasopharyngeal carcinoma(NPC).Materials and Methods From Sep 2006 to Dec 2006,20 patients with newly diagnosed primary NPC,who underwent IMRT at radiothapy department of the first affiliated hospital of guangxi medical university,were enrolled to this dosimetric study.All patients were confirmativly diagnosed by MRI and pathology,partly received ECT/PET-CT scanning.Every patient was simultaneously performed three plans,that is,2DRT,2DRT+3D Boost and IMRT.The distinction of these plans lied in nasophynx and upper neck,and the node areas of lower neck and top of clavicle were uniformiy irradiated with a single conventional anterior portal.The treatment planning was orderly accomplished through the procedure of mask setup,CT-sim scan,image delivery and register, target delineation,dose prescription,plan design,assessment and determination. The gross tumor volume(GTV)included palpable and visible nasopharyngeal tumor and involved lymph nodes of more than 1cm diameter.The clinical target volume(CTV)modeled two regions considered to represent differrent risks. CTV1 encompassed the GTV with 5-10mm margin of adjacent tissues.CTV2 encompassed ipsilateral or contralateral elective nodal regions at risk of harboring microscopic tumor.The treatment planning was provided using a commercial IMRT treatment planning system(Version 7.6C,Pinncal syetem, PHILIPS).The dose planned for target volume was PTVnx68-74Gy,PTVnd 62-70Gy,PTV₁60-64Gy,PTV₂54Gy,respectively.2DRT was performed through 4 segmentation boost adopting conventional fraction,and 2DRT+3DCRT Boost, the fomer 2 courses of which was identical with 2DRT,was boosted with 3DRT during the later 2 courses.IMRT was executed with simultaneous modulated accelerated radiotherapy boost technique(SMART),or rather,the fractionation schedule was completed in 6 weeks with 5 daily fractions weekly prescribing PTVnx2.27-2.47Gy/Fx,PTVnd2.07-2.33Gy/Fx,PTV₁2.0-2.13Gy/Fx,PTV₂1.8 Gy/Fx.Dose-volume histograms was employed to analyze the dose distributions and irradiated volumes of targets and critical organs.The main estimate index of target volumes included Dmin,Dmax,Dmean,D99,D95,D90,D5,V105,V100, V95,V90,CI,HI.The serial sensitive organs,such as spinal cord,brain stem,len, optical nerve,optical chiasma etc,were mostly assessed by Dmax,Dmean,and the parallel sensitive organs by Dmean,D33 or D50,such as parotid gland,temporal lobe,temporal-madibula joint etc,moreover,all organs at risk were combined with a certain volume-dose(Dx)and dose-volume(Vx)to valuate dose distributions.Results The Dmean,D95,V105,V100,V95,CI,HI of target volume were as follow(IMRT/2DRT/2DRT+3D Boost),respctively,GTVnx:79.3Gy/70.6Gy/70.7 Gy,74.4Gy/68.1Gy/68.4Gy,92.7%/4.99%/1.74%,99.2%/45.4%/48.6%,99.9%/96.2 %/98.1%,0.99/0.96/0.98,1.16/1.09/1.08;PTVnx:77.3Gy/70.2Gy/70.4Gy,70.2 Gy/66.0Gy/66.SGy,78.0%/4.94%/2.09%,93.1%/42.0%/45.7%,98.2%/89.7%/92.9 %,0.98/0.89/0.93,1.25/1.15/1.12;CTV1:75.TGy/69.TGy/69.SGy,66.SGy/64.3 Gy/65.1Gy,96.9%/90.3%/93.5%,99.2%/97.3%/98.8%,99.7%/99.7%/99.9%,1.00/ 1.00/1.00,1.61/1.31/1.24;PTV1:72.5Gy/68.SGy/68.7Gy,61.0Gy/61.0Gy/62.3 Gy,4.7%/78.6%/84.4%,93.1%/90.4%/94.4%,97.1%/97.2%/98.8%,0.97/0.97/0.99, 1.46/1.29/1.22;CTV2:69.2Gy/64.4Gy/64.7Gy,58.5Gy/50.9Gy/51.6Gy,96.5 %/84.1%/86.1%,98.8%/90.3%/91.6%,99.5%/93.9%/95.0%,1.00/0.94/0.95,1.49/ 1.88/1.86;PTV2:66.6Gy/61.SGy/63.7Gy,53.3Gy/44.9Gy/45.7Gy,89.5%/73.2% /76.4%,94.0%/81.0%/83.7%,96.3%/87.1%/88.4%,0.96/0.87/0.88,1.81/2.14/2.11.The relativeship between dose and volume of sensitive organs were as follow(IMRT/2DRT/2DRT+3D Boost).Spinal cord:the Dmax,Dmean,Dlcc was, respectively,46.6Gy/47.7Gy/51.0Gy,37.1Gy/37.4Gy/38.6Gy,42.9Gy/42.8Gy/45.8 Gy.Brain stem:the Dmax,Dmean,D3 was,respectively,57.5Gy/60.2Gy/63.2 Gy, 35.0Gy/18.4Gy/20.2Gy,52.3Gy/53.1Gy/57.0Gy.Pituitary:theDmax,Dmean, V50Gy was,respectively,48.4Gy/48.3Gy/48.8Gy,43.8Gy/41.6Gy/42.0Gy, 23.6%/37.4%/38.2%.Optical chiasma:the Dmax,Dmean,V50Gy was,respecttively, 47.6 Gy/42.6Gy/42.7Gy,42.0Gy/36.1 Gy/3 6.5Gy,27.9%/27.1%/28.2%. Optical nerve:the Dmax,Dmean,V50Gy of the right was,respectively,43.1Gy/ 42.5Gy/42.4Gy,31.0Gy/32.5Gy/32.6Gy,13.3%/27.6%/31.1%;and that of the left was 44.8Gy/43.3Gy/43.3Gy,33.3Gy/32.2Gy/32.3Gy,11.6%/25.8%/26.5%. Lens:the Dmax,Dmean,V8Gy of the right was,respectively,7.90Gy/5.24Gy/ 5.90Gy,6.69Gy/3.26Gy/3.64Gy,9.6%/5.2%/8.0%;and that of the left was 8.43 Gy/4.78Gy/5.56Gy,7.09Gy/3.15Gy/3.55Gy,16.3%/6.3%/7.4%. Mandibula:Respectively,the Dmean,D33,V60Gy of the right was 43.5Gy/ 35.8Gy/35.1Gy,47.9Gy/60.9Gy/60.0Gy,3.9%/35.3%/35.6%;and that of the left was 45.1Gy/36.9Gy/34.9Gy,49.4Gy/59.6 Gy/59.4Gy,5.9%/34.8%/36.5%. TMJ:the Dmean,D33,V60Gy of the right was,respectively,43.6Gy/ 67.0Gy/64.1Gy,45.5 Gy/67.6Gy/64.7Gy,0.3%/94.3%/79.2%;and that of the left was 45.8Gy/67.1Gy/63.1Gy,48.8Gy/68.1Gy/65.0Gy,4.8%/92.4%/83.6%. Middle ear:Respectively,the Dmean,D50,V55Gy of the rihgt was 49.1Gy/ 44.3Gy/46.4Gy,49.4Gy/45.6Gy/47.5Gy,13.7%/25.9%/30.9%1 and that of the left was 47.3Gy/45.4Gy/47.2Gy,47.6Gy/46.3Gy/48.3Gy,20.2%/32.2%/37.4%. Temporal lobe:the Dmean,D10,V60Gy of the right was,respectively,34.1Gy/ 18.9Gy/18.8Gy,50.8Gy/57.5Gy/56.9Gy,5.0%/10.3%/9.4%;and that of the left was 26.0Gy/19.0Gy/19.1Gy,50.9Gy/57.4Gy/56.8Gy,6.5%/10.5%/9.8%.Parotid gland:Respectively,the Dmean,D33,V32Gy was,respectively,40.6Gy/64.7Gy/ 62.4Gy,43.5Gy/68.9Gy/65.8Gy,66.0%/99.8%/99.9%;and that of the left was 39.7Gy/64.3Gy/61.7Gy,43.3Gy/68.2Gy/64.9Gy,66.5%/99.6%/99.7%.Parotid gland outside target:the Dmean,D33,V32Gy was,respectively,30.3Gy/63.7Gy/ 60.7Gy,31.8Gy/67.8Gy/63.9Gy,34.6%/99.7%/99.8%;and that of the left was 30.4Gy/62.8Gy/59.5Gy,32.1Gy/67.4Gy/62.9Gy,38.1%/99.3%/99.3%.For IMRT,all target volume was negative interrelated with conformity index(CI)but positive with heterogeneity index(HI)in correlation analysis, which was merely similar to GTVnx for 2DRT and 2DRT+3D Boost.Conclusions Target volume:â‘ All three treatment plannings could provide quite good dose distributions.â‘¡IMRT's dose degree is highest offering dosimetric advantages especially T-advanced stage patients.â‘¢IMRY products the worst dose uniformity at GTVnv/PTVnv and CTV1/PTV1.â‘£IMRT possess optimal dosimetric uniformity and distributions for CTV2/PTV2 and 2DRT is the worst.⑤the bigger target volume,the worse conformity and the more heterogenous to IMRT.â‘¥2DRT+3D Boost possess somewhat better dosimetric painting than 2DRT.⑦2DRT+3D Boost provides optimal dosimetric uniformity for GTVnx/PTVnx and CTV1/PTV1.yet it's conformity of GTVnx,alike 2DRY, turns worse with GYVnx-volume increase.Organs at risk:â‘ IMRY provides optimum normal tissue sparing for all patients.â‘¡2DRY and 2DRT+3D Boost can provide satified normal tissue spring for T2 and T3 stage patients except for TMJ and parotid gland.â‘¢Yhe dosimetric advantages of 2DRT+3D Boost plan to 2DRT represents at parotid gland,TMJ and mandibula,that is scarce to other normal tissues.