The Comparative Study Of Conventional Radiotherapy And Intensity Modulated Radiotherapy For Nasopharyngeal Carcinoma

Objective:To compare the dose distribution of conventional radiotherapy with intensity modulated radiotherapy(IMRT)in the treatment of nasopharyngeal carcinoma and investigate advantages of different radiotherapy techniques.Methods:From April 2007 to September 2007 fifteen patients diagnosed with na(?)ve primary nasopharyngeal carcinoma by pathobiopsy were selected including 9 males and 6 females.The median age at diagnosis was 44 years(range 21～63 years).All of their histological types were low differentiated squamous cell carcinoma.All patients were staged using the 2002 Fu Zhou classification,2 in stageⅠ,2 in stageⅡ,7 in stageⅢand 4 in stageⅣa.After CT scan,CT images were transported to Philips Pinnacle3 inverse Treatment Planning System.Conventional radiotherapy and IMRT plans were made for each of them after target volume and critical normal tissues were outlined on all CT slices in which the structures exist.Treatment was delivered with the VARIAN2100C/D. Analyse doses delivered to target volumes and critical normal tissues by dose volume histogram,and compare two plans with target coverage (V95),normal tissue complication probability(NTCP)and normal tissue sparing(D5,D50 and D33,etc).Record and grade acute normal tissue radiation effects according to RTOG radiation morbidity scoring criteria, simultaneously observe 15 patients with primary nasopharyngeal carcinoma who received conventional radiotherapy.Results:Analysis of dose volume histogram showed that the average mean dose delivered in conventional radiotherapy and IMRT were 71.71Gy and 73.2Gy to PGTVnx;65.1Gy and 72.06Gy to GTVnd; 62.45Gy and 66.84Gy to PTV1;51.92Gy and 55.10Gy to PTV2, respectively.The average volumes of all target volumes covered by 95% isodose were more than 96%(range 96.83%-99.99%)in IMRT,oppositely average volumes of all target volumes covered by 95%isodose were less than 95%in conventional radiotherapy.IMRT had satisfied dose coverage of target volume especially in subclinical lesion region compared with conventional radiotherapy.5%of brain stem volume,lcc of spinal cord volume,50%of parotid gland(R)volume,33%of TMJ volume,5%of optic nerve(R)volume received average dosage in conventional radiotherapy and IMRT respectively were:conventional radiotherapy: 48.16Gy,47.55Gy,67.26Gy,71.66Gy and 56.56Gy;IMRT:38.49Gy, 34.11Gy,30.28Gy,35.63Gy and 27.19Gy.Acute radiation effect was well tolerated,only one in conventional radiotherapy group had treatment break for five days due to Grade 3 acute radiation effects of mucous membrane and skin,one in IMRT group had treatment break for four days due to Grade 3 acute radiation effects of mucous membrane and pharynx. Both of them had receive concurrent chemoradiation.There was no Grade 4 acute radiation effect in all patients.In conventional radiotherapy patients,most showed Grade 2 and Grade 3 acute effects.Patients received IMRT had obviously less Grade 3 acute effects than patients in conventional radiotherapy groups,most of them had Grade 1 and Grade 2 acute effects meanwhile two patients complainted no symptom of xerostomia.Incidences of acute Grade 3 radiation effects of mucous membrane,skin and pharynx were 33.3%,33.3%and 20%in conventional radiotherapy;13.3%,6.7%and 13.3%in IMRT, respectively.Conclusion:①IMRT can escalate the total dose to target volumes uniformly,provide satisfied target volume coverage for NPC than conventional radiotherapy.②IMRT could decrease the irradiation dose to adjacent critical organs and lessen the acute radiotherapy effects effectively.