Study Of Hippocampal Formation Protection In IMRT Of Nasopharyngeal Carcinoma

Objective: To observe the hippocampus formation dosimetry differences and thepotential damage of relevant function in intensity-modulated radiotherapy （IMRT）ofnasopharyngeal carcinoma （NPC）,and probe necessity and feasibility ofhippocampal-sparing in the radiotherapyMethods:1.The Optimization design data of59patients with different stages ofnasopharyngeal carcinoma for IMRT were analyzed retrospectively., and combinedwith the CT-MR image fusion technology to draw the outline of the hippocampusformation, hippocampus formation dosimetry differences of different tumor T stagewere reviewed, including Dmax and Dmean, D20, and V₂₀, etc.2. Sensitive items ofWechsler Adult Memory Scale were used to compare the neurocognitive functionrelated with memory of51patients one year after radiotherapy,and compare thedifferences of the memory test results between the Before radiotherapy group（n=30）and Health group（n=30）.3.Optimization design plan with or withoutshippocampal-sparing （plan II and plan I） of the T3-4stage cases were compared ondosimetry differences of hippocampal formation, The tumor of target area and otherorgan at risk.Results:1.For59NPC cases, the hippocampal formation maximum doses ranged from11.1to78.2Gy （mean,52.3Gy）,mean doses ranged from3.2to44.6Gy （mean,18.7Gy）, D20ranged from4.5to64.1Gy （mean,29.0Gy）, V₂₀ranged from0to87.1%（mean,35.7%）. Irradiation dose of T3-4stage is significantly higher than that of the T1-2stage,with maximum doses and mean doses were58.6±14.8Gy，21.8±9.3Gy respectively.2.There were no difference between the Before radiotherapy group and Health group inAssociate Learling （AL）, Accumulation, Digit Span（DS） and Visual Reproduction（VR）,on the countrary,they were statistically differenct between T3-4stage groupand T1-2stage group,except DS.3.In the optimizing design of hippocampal-sparing（plan II）,radiation dose of hippocampal formation was significantly lower than plan I, Dmean reduced from21.8Gy to15.3Gy （29.8%reduction）, D20mean reduced38.1%,radiation volume of received more than20Gy was deeply decrease （>55%） withno significant effection to tumor of target area t and other organ at risk.Conclusions:In the IMRT of NPC, hippocampal formation may be received largeirradiation dose, especially in T3-4stage, and combine with the tendency of relevantcognitive function impairment;Using IMRT with hippocampal-sparing cansignificantly reduce the hippocampus formation’s radiation dose, with no significanteffect on the tumor of target area and other organ at risk. Therefore, the effect ofradiantion on hippocampus formation deserve seriously attention in the IMRT ofNPC.