ABSTRACT
Objective To compare the single-shot fields irradiated by three focusing modes of γ-knife and explore the approaches for improving the quality of stereotactic radiosurgery.Methods GAFCHROMIC(R) EBT3 mode flushing-free film was used to measure the single-shot fields irradiated by multi-source static focusing modes,multi-source single-axis rotating focusing mode and single-source double-axis rotating focusing mode of γ-knife.Also the uniformity and penumbra of the single-shot fields were compared.Results The 2D dose distribution of the single-shot fields irradiated by three focusing modes of γ-knife was different.In the axis (x,y,z),the rang of penumbra axial length ratios of multisource static focusing modes,multi-source single-axis rotating focusing mode and single-source double-axis rotating focusing mode were 0.13-0.48,0.17-0.33 and 0.28-0.54,in the diagonal direction of the wings plane (NSD,PSD),were 0.31-0.39,0.38-0.43 and 0.54-0.72,respectively;the penumbra axial length ratio of single-source double-axis rotating focusing mode was bigger than in multi-source static focusing modes and multi-source single-axis rotating focusing mode.On the no-wings plane,the area ratios of 80％ dose curve enveloped and 50％ dose curve enveloped(A80％/A50％)were 0.40,0.47 and 0.19,on the wings plane,were 0.61,0.53 and 0.35,respectively.The field uniformity of multi-source static focusing modes and multi-source single-axis rotating focusing mode were superior to single-source doubleaxis rotating focusing mode.Conclusions Considering dose distribution of the single-shot fields,the multi-source static focusing modes devices and the multi-source single-axis rotating focusing mode devices should be preferred,when important tissues and organs are adjacent to the target areas.Compared with single-source double-axis rotating focusing mode,both multi-source static focusing modes and multi-source single-axis rotating focusing mode could make more target areas to be surrounded by high dose region.
ABSTRACT
Objective To measure 222Rn and 220Rn concentrations in the underground non-uranium mines in Shandong Province,and to estimate the annual effective dose to the miners.Methods Concentrations of 222Rn and 220Rn in selected gold,iron,coal and clay mines were determined by passive time-integrating detectors with CR-39.Activity concentrations of 226Ra,232Th and 40K were determined using gamma spectrometry equipped with HPGe detector.Results The average concentrations of 220Rn in the gold,iron,coal and clay mines were estimated to be 1200,280,120 and 40 Bq/m3,respectively.The activity concentrations of 226Ra,232Th,40K in the ores for gold,iron,coal and clay mines ranged the same as the soil in China.The annual effective dose due to radon exposure in gold and iron mine was 7.70 mSv and 1.74 mSv,respectively.The annual doses received by miners in the coal and clay mines were lower than 1 mSv.Conclusions Underground miners in some gold and iron mines should be treated as workers occupationally exposed to ionizing radiation.The measurement such as increasing ventilation should be implemented to reduce underground radon concentration in these mines.
ABSTRACT
Objective To investigate the chromosome damage in peripheral lymphocytes of underground gold miners.Methods Conventional method and cytokinesis-block micronuclens assay were used to analyze frequency of chromosome aberrations and micronucleus in peripheral lymphocytes in 58 gold miners,respectively.Results Frequencies of chromosome-type aberrations,ehromatid-type aberrations and total aberrations were higher in the miners than those in the control group(0.72%,0.41%,1.16% vs 0.14%,0.18%,0.33,X2=44.322,9.501,50.476,P＜0.01).Both micronucleated cell rate and micronucleus rate were higher in the miners group than those in the control group(10.8‰ and 11.6‰ vs 8.7‰ and 9.0‰,X2=8.672,12.546,P＜0.01).Frequencies of chromosomal aberrations and micronucleus proportionally increased with underground working years.Compared with those miners who had worked underground 6 years or shorter,both frequencies were statistically higher among the miners who had worked underground for more than 21 years(P＜0.05).No difference was found among other groups of working years(P＞0.05).Compared with the control group,both frequencies increased in the miner group,and the differences were statistically significant(X2=2.395,P＜0.05 for chromosomal aberrations and X2=2.319,P＜0.05,respecfvely).The common types of chromosome aberrations were acentrie fragments,while chromatid break and dicenrics were subordinate.Conclusions Chromosomal damages were observed in the gold workers who exposed high radon in the underground mining.