| [Backgrounds]With the development of radiation techniques,intensity modulated radiation therapy is used more and more widely,especially in the head and neck tumors.IMRT have many advantages.Compared to the conventional radiotherapy,The position of nasopharyngeal carcinoma is deep,radiotherapy target's shape is highly irregular,IMRT has good conformal degree which can reduce the surrounding normal tissue dose,at the same time can greatly improve target dose.Different location need different dose in target zone,the position of primary tumor and metastatic lymph node need high dose,while the prevention area need low dose,so the dose in the target zone need to distribution according to the requirements.Besides,near the nasopharyngeal carcinoma has the more endanger organs,such as parotid gland,brainstem,spinal cord and so on,which position is relatively close and complex to the target.IMRT can reduce the radiotherapy side effects of the surrounding tissue and improve the patient's survival rate,at the same time can preserve and improve the patient's life quality.The rate of neck lymph node metastasis of nasopharyngeal carcinoma is higher,about 80%-90%patients with the first treament have lymph node metastasis,which ? aera lymph node of neck is more common.lymph nodes of ? aera through the lymphatic network river after ? area down to the supraclavicular,lymph nodes's jumping transfer rate is low.The rate of lymph node metastasis of ?,?,? aeras are about 95.5%,60.7%and 34.8%.The rate of parotid lymph node in nasopharyngeal carcinoma is very low,which have literature report is about 1.4%to 3.4[1-2].The common drainage area of Parotid lymph node are scalp,facial,eye,outer ear,etc,and the not common drainage areas are nasal,sinuses,nasopharyngeal and oral cavity.Parotid gland metastases of nasopharyngeal carcinoma are rare,and the function of the parotid gland with secretion of saliva is affecting the quality life of patients,parotid gland in the IMRT of nasopharyngeal carcinoma is as a protected organ.the parotid gland dose of intensity-modulated radiation therapy in nasopharyngeal carcinoma(NPC)is usually set 50%of parotid gland volume not more than 30 Gy or mean dose not more than 26 Gy[3].Parotid lymph node metastasis of nasopharyngeal carcinoma after IMRT have been constantly reported,we did not see parotid lymph node metastasis happened after the CRT.May be in the CRT of nasopharyngeal carcinoma,bilateral parotid are included within the radiation field,all of the parotid gland volume is radiationed,and the secretion of saliva is serious decline,which can cause adverse reactions such as dry mouth.The raditioned dose and volume of parotid gland of nasopharyngeal carcinoma(NPC)with IMRT was lower than those of CRT,and thus improve the function of the parotid gland secretion,reduce the incidence rate of the dry mouth,improve the survival quality of patients,but the probability of parotid lymph node metastas is improved.[Objective]The purposes of this study:(1)By comparing the dose distribution in the parotid gland and target area of nasopharyngeal carcinoma with IMRT and CRT,the probability of two groups of parotid lymph node metastasis were retrospectively analyzed.(2)By observing the characteristics of cases which parotid lymph node metastasis of nasopharyngeal carcinoma with IMRT are prone to happend.It can provide clinical value for parotid gland dose limit.[Methods]Selected 323 cases of nasopharyngeal carcinoma with IMRT in our hospital from January of 2009 to December Of 2015,with the confirmed pathology;Besides,choosed 312 cases of nasopharyngeal carcinoma with CRT from January 2003 to December of 2009.Understand the dose distribution of target area and the parotid gland of nasopharyngeal carcinoma with IMRT and CRT,getting regularly through reviewing literature and similar case report.[Results]In nasopharyngeal carcinoma IMRT group,3 patients respectively occurred parotid lymph node metastasis after IMRT in 1 and a half years,7 months and 6 years.3 cases were located in the superficial parotid gland.1 cases confirmed by pathology and then made parotid resection and postoperative chemoradiotherapy.1 case discovered by ultrasound imaging,another by the CT imaging.No parotid lymph node metastasis happened in Nasopharyngeal carcinoma at CRT group.1 case have a history of the cervical lymph nodes biopsy and have a huge lymph node in parapharyngeal space.The other 2 cases were found enlarged lymph nodes in the II area of neck,and parotid gland metastases both occured in shallow lobe of the parotid gland.Because of nasopharyngeal carcinoma is sensitive to radiation therapy,radiation therapy of nasopharyngeal carcinoma is the preferred treatment.In IMRT treatment of nasopharyngeal carcinoma,the target dose of nasopharyngeal carcinoma is usually set at 69.96 Gy/33f,.In CRT treatment of nasopharyngeal carcinoma,the target dose of nasopharyngeal carcinoma is usually set at 70 Gy/30f.The dose of parotid gland is usually restricted to V30 is less than 50%or less than 26 Gy in the average dose of parotid gland.And when the CRT nasopharyngeal carcinoma target prescription dose reaches 70 Gy,bilateral parotid doses is close to 70 Gy.[Conclusions]In this study having about 0.93%incidence of parotid metastasis after radiotherapy of nasopharyngeal carcinoma,incidence rate is extremely low.Intensity modulated radiation therapy of nasopharyngeal carcinoma is still in accordance with the standard dose limit to protect the function of the parotid gland.For patients with huge lymph nodes at parapharyngeal space;swollen lymph nodes in the II area of neck;huge or more neck lymph node number;destroyed normal lymphatic drainage way by previous neck surgery or radiation therapy,the author thinks when making such radiotherapy treament should be based on actual situation,extending the limitation on the dose of ipsilateral parotid gland,at the same time,strengthening the protection of the parotid gland on the other side. |
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