| Objective: To analyze the difference of the dose distribution between theIMRT plans and the2DCRT plans in the treatment planning system throughsimulating the2DCRT plans and IMRT plans,further providing the assistancefor clinical practice.Materials and Methods: From June2012to January2013,15patientswith nasopharyngeal carcinoma received IMRT in the Beijing Military RegionGeneral Hospital. The target area of the IMRT requirement was in accordancewith the "nasopharyngeal carcinoma after radiotherapy of head and neckcancer atlas--second edition" and2DCRT faciocervical portal and shrinkingfield were simulated on DRR. Designing the IMRT plans and simulating the2DCRT plans on the DRR for15NPC with the Pinnacle39.2f treatmentplanning system, respectively, each patient have two sets of plans and Dosecurve figures. Then compare the Dose in IMRT and2DCRT plans.The2DCRTplan: in the first stage, two-sided faciocervical portal field+anterior tangentialfield of the under neck36Gy.In the second phase, two-sided shrinkingfaciocervical portal field (occlusion spinal cord)+the bilateral back neck areaelectronic field of24Gy+under anterior tangent field14Gy. If the neck hadpositive lymph nodes, irridate the node till total70Gy using electronic energy.Thirdly, complete the amount of10Gy binaural of Maeno±neck electronicenergy for positive lymph nodes10Gy. Based on the centralplane,nasopharyngeal tumors and metastatic lymph nodes reached70Gy,double side of the faciocervical and back of the neck area up to60Gy,50Gylower neck supraclavicular area. IMRT plan: GTVnx is the tumor which canbe seen in the Imaging; GTVnd is metastatic lymph nodes; GTVnx expand20~30mm backwards, and5mm~10mm in other directions to form pGTVnx.CTV1is subclinical lesions,including nasopharynx, skullbase,retropharyngeal space, the lower part of the sphenoid sinus, thepterygomandibular fossa, nasal and third maxillary sinusand high-risklymphatic metastatic area. CTV2is the neck prevention irradiated areas. PTVwas extroverted from CTV in3mm, and near anatomical structure withappropriate amendments.The prescription dose is pGTVnx70Gy, PTV160Gy,PTV250~60Gy. Analyze the dose difference of the GTVnx, GTVnd, CTV1,Skull base area, Region Choanarum, Parapharyngeal space, Pterygopalatinefossa, Cochlea and Parotid superficial lymph nodes area and IA, IIA, IIBlymphatic drainage area between the two radiotherapy plans. The analysissoftware is SPSS13.0.Results:1The GTVnx DoseD95, Dmean, Dmin, V70, V60of IMRT are6.11%,3.05%,35.54%,15.91%,0.22%higher than that of the2DCRT, P <0.01. There is nosignificant difference of Dmax.2The GTVnd DoseV66, Dmin of IMRT is8.12%,13.94%higher than that of the2DCRT, P<0.05. No significant differences are found in D95, Dmax, Dmean, V70.3The CTV1DoseD95, Dmean, Dmin, V60of IMRT are5.65%,9.15%,275%,8.78%higher than that of2DCRT, P <0.05. There is no difference in Dmax.4The Skull base area DoseDmin of IMRT is56.17%greater than that of2DCRT, P=0.002. Thereare no obvious difference in D95, Dmean, Dmax, V70, V60.5The Region Choanarum DoseD95, Dmean, V70of IMRT are less than2DCRT, reducing the proportionof5.41%,2.36%,44.69%, P<0.05. Dmax is greater than that of2DCRT,increasing the proportion of3.58%, P=0.000. There are no obvious differencein Dmin and V60. 6The Parapharyngeal space Dose6.1Pre-styloid SpaceD95, Dmean, V70of IMRT are less than2DCRT, reducing the proportionof7.33%,7.26%,57.57%, P<0.05. There are no obvious difference in Dmax,Dmin, V60.6.2Post-styloid SpaceD95, Dmax, Dmean, Dmin, V70, V60of IMRT are9.52%,5.22%，6.06%,23.37%，47.0%，7.86%higher than2DCRT, P<0.05. There are no obviousdifference in Dmax, Dmin, V607The Pterygopalatine fossa DoseD95of IMRT is4.17%higher than2DCRT, P=0.048. V70of IMRT is68.41%less than that of2DCRT, P=0.001. There are no obvious difference inDmean, Dmax, Dmin, V60.8The Lymphatic drainage area Dose8.1Lymphatic drainage area of IIADmax, Dmean, V70of IMRT are9.38%,6.67%less than2DCRT,P<0.05. Dmin of IMRT is11.97%higher than that of2DCRT, P=0.004. Thereare no obvious difference in D95, V60.8.2Lymphatic drainage area of IIBDmax of IMRT is7.39%less than that of2DCRT, P=0.007. D95, Dmin,V60of IMRT are10.19%,29.51%,12.19%higher than2DCRT, P<0.05.There are no obvious difference in Dmean, V70.8.3Lymphatic drainage area of IAD95, Dmean, Dmin of IMRT are535%,66.83%,808%higher than thatof2DRT, P<0.05. There are no obvious difference in Dmax, V60.8.4Parotid superficial lymph nodesDmax, Dmean, V70, V60, V40of IMRT are37.13%,38.03%,100%,99.85%,76.38%less than that of2DCRT, Dmin of IMRT is82.54%highrthan2DCRT, P<0.05. There are no obvious difference in D95, V20.9The Parotid gland Dose9.1Parotid gland of the ipsilateral GTVnxD45, D50, Dmean, V50, V40, V30, V20of IMRT are64.63%,64.57%, 54.51%,94.03%,81.53%,66.20%,38.35%less than that of2DCRT, P<0.05.9.2Parotid gland of the contralateral GTVnxD45, D50, Dmean, V50, V40, V30, V20of IMRT are55.17%,58.08%,54.77%,82.89%,71.39%,60.28%,31.52%less than that of2DCRT, P<0.05.10The Cochlea DoseD95, Dmean, Dmin, V50of IMRT are higer than that of2DCRT,increasing the ratio of229%,91.01%,286%,197%, P<0.05. There is noobvious difference in Dmax, V70, V60.Conclusion：1IMRT planning in tumor coverage is significantly superior to2DCRTplans and normal organs have a lower doses in IMRT than that of2DCRT.2Because of the reccurence of nasopharyngeal carcinoma treated withIMRT located in the multi-drop dose districts, we need to further improve theintensity-modulated target and standard the Dose of irradiation rang and thedifferent relapse parts. At the same time improving the efficacy, further reducethe incidence of complications and improve the patients’quality of life. |
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