The Experimental Study Of Iodine-131 Brachytherapy For Brain Gliomas

Objectives:(1)To investigate the dosimetric medicine of ¹³¹I brachytherapy for brain gliomas using a novel ¹³¹I liquid-filled brachytherapy cyst,designed for the treatment of malignant brain-tumor resection-cavity margins.(2)To calculate the effective dose and sufficient cell-killing dose rate of ¹³¹I brachytherapy for the cultured C6 glioma cell in order to clinical treatment write-in scale.(3)To establish a SD rat model for ¹³¹I brachytherapy using the device,and furthermore to investigate the potential earlier alteration of radiation-induced brain toxicity in rat brain tissue following exposure to ¹³¹I and initially calculate the tolerance dose.Methods:(1)To establish a mathematic model of the ¹³¹I-containing radiotherapy cyst in isoeffect homogeneous media to understand the dosimetry properties by Monte Carlo simulation or mathematics calculation.(2)The apoptosis ratio and survival fraction of the cultured C6 glioma cells were detected periodically every 4 days by cloning efficiency and flow cytometry with Annexin V-FITC/PI double staining after the C6 cell radiated for 72 hours by 60mCi ¹³¹I in a distance of 5mm and 30mm.(3)The geometry of radiotherapy cyst was detected by CT scan after implanted onto rat brain surface by surgical procedure.(4)Twelve SD rats were randomly divided into four groups exposed respectively to ¹³¹I of 0 mCi,10 mCi, 30 mCi,60 mCi.The head CT scan was performed before and 8 days,32days after exposure.All rats were killed in 32days collecting cerebral hemisphere specimen for HE Staining and transmission electron microscope pathological examination.Results:(1)The ¹³¹I radiotherapy cyst delivers irradiation dose at either a low dose-rate or a sub-low dose rate owing to high-energy gamma-emitting ¹³¹I.The dose-rate for the ¹³¹I radiotherapy cyst to isoeffect homogeneous media decreased non-linearly related to time axis and distance.There is a proportional relation between the dose-rate or total absorbed dose at a definite distance and the primary activity of ¹³¹I.(2)Partial C6 glioma cells were killed or induced apoptosis following exposure to ¹³¹I for 72 hours,and the maximum apoptosis ratio was 16.42±1.66%。Meanwhile,necrotic cell death has been found.The survival fraction of C6 glioma cells also decreased owing to irradiation and the minimum value was 59.0±2.39%.(3)At a dose-rate of less than 400mGy/h irradiation can also induce apoptosis of C6 cells.The effectively cell-killing dose-rate of C6 glioma radiated by ¹³¹I was larger than,and equals to 47.64-61.65mGy/h and the accumulative dose 3.9Gy for 72 hours.However,in the interval of 186.6-677.8 mGy/h,increasing dose rates irradiation resulted in decreased C6 cell killing.(4) When the accumulative total absorbed dose to rat brain tissue was more than 177.11Gy in 32 days,the pathological change of some areas of these rats brain exhibited following histopathological characteristics:colliquative necrosis and coagulation necrosis in which main normal ultrastructure involving neuroglial cell and myelin sheaths disappeared,embolism intro-capillary,adjacent brain tissue swelling,and vascellum lumina embolism.Surrouding brain tissues were swelling as well as location myelinolysis,degranulation and flocculent degeneration of chondriosomes.(5)The pathological change did not be observed on the brain specimen that absorbed dose was less than 96Gy.Conclusions:(1)The radiotherapy cyst filled with ¹³¹I solution is suitable for LDR and SLDR brachytherapy.The absorbed dose and dose rate to the media in a definite distance to radiotherapy cyst can be adjusted by injecting various initial activity of ¹³¹I.(2)The C6 glioma cells can be partly induced apoptosis after exposure to ¹³¹I radiotherapy cyst in a definite distance for 72 hours.The effectively cell-killing dose-rate to C6 ceils delivered by ^<sup>131I radiotherapy cyst was larger than,and equals to 47.64-61.65 mGy/h,and the accumulative dose 3.9Gy for 72 hours.(3)The tolerance dose to rat brain tissue under ¹³¹I radiotherapy was 4 times higher than that under external beam radiation.The safely absorbed dose to rat brain tissue is lower than 96Gy using this ¹³¹I radiotherapy cyst in early period of ¹³¹I brachytherapy.