Study Of Radiation-Induced Lower Cranial Neuropathy After Radiotherapy In Patients With Nasopharyngeal Carcinoma

Abstract Objective : To study the risk factors forradiation-induced lower cranial neuropathy (RILCN) after radiotherapy inpatients with nasopharyngeal carcinoma, and to compare the maximumirradiation doses and complication probabilities of lower cranial nerve inusing different conventional external irradiation technique to treat thepatients, and to help design the radiotherapeutic planning. Methods:Toobserve retrospectively 300 patients with nasopharyngeal carcinoma whoreceived radical radiotherapy through a 1:2 pair-matching case-controlstudy, and analyze the risk factors that might cause RILCN by using theconditional logistic regression model. And to design respectively threeconventional external irradiation treatment plans onto the every CT imageof ten patients with nasopharyngeal carcinoma by using three-dimensionaltreatment planning system(Plan A, initially using two lateral faciocervialportals plus inferior neck tangential portal to 36Gy, followed by twocontracted faciocervial portals plus inferior neck tangential portal to 50Gy;Plan B, initially using two lateral faciocervial portals plus inferior necktangential portal to 36Gy, followed by two pre-auricular portals plus wholeneck tangential portal to 50Gy; Plan C, directly using two pre-auricularportals plus whole neck tangential portal to 50Gy. All of the three plansend up by using two pre-auricular portals boosted to 72Gy.), then tocompare the difference of their maximum doses and normal tissuecomplication probabilities(NTCP) of the carotid sheath throughdose-volume histogram, and estimate the probability of developing RILCNaccording to the NTCP of carotid sheath. Results: The chosen factorsin the Logistic regression formula were smoking, external irradiationtechnique, dose of radiation to superior neck, neck fibrosis and acuteradiation-related dermatitis of neck, whose hazard ratios were 4.358, 2.231,3.077, 4.397 and 2.689, respectively. There was a high dose region onsubmandibular region because of the overlapping between pre-auricularportal and whole neck tangential portal which was found from thetreatment planning system. The mean vectors of the maximum dose of boththe left carotid sheath and right carotid sheath by using the three differentexternal irradiation techniques were X = (77.72,76.85)', X = (83.89,83.78)' A Band X C = (105.97,106.11)' .There was significant difference among them(F=55.003,P<0.05). The mean vectors of the NTCP of both carotidsheaths by using the three different techniques wereX = (36.4,35.0)' , X = (52.2,49.6)' A B and X = (94.8,95.0)' . C There wassignificant difference among them(F=36.901,P<0.05)also. And therewas significant difference in the mean vectors of both maximum dose andNTCP between plan A and B, plan A and C, or plan B and C, respectively(the values of Probability all less than 0.05). There were the lowestmaximum dose and the lowest NTCP of carotid sheath by using plan A,while the highest ones when using plan C. Conclusions:Smoking,external irradiation technique, the dose of radiation to superior neck ,neckfibrosis and acute radiation-related dermatitis of neck were the risk factorsfor developing RILCN. Using the irradiation technique of pre-auricularportal plus whole neck tangential portal increases the maximum dose andNTCP of carotid sheath because of their overlapping on the submandibularregion, and then probably increases the incidence of RILCN afterradiotherapy in the patients with nasopharyngeal carcinoma. Thus, tosuggest abandoning the irradiation technique of pre-auricular portal pluswhole neck tangential portal.