de Lima Alexandre Roza, Hunt John Graham, Da Silva Francisco Cesar Augusto
Institute of Radiation Protection and Dosimetry, Av. Salvador Allende, s/n, Barra da Tijuca, Rio de Janeiro, CEP 22783-127, Brazil.
J Radiol Prot. 2017 Dec;37(4):852-863. doi: 10.1088/1361-6498/aa7f06.
The ICRP Statement on Tissue Reactions (2011), based on epidemiological evidence, recommended a reduction for the eye lens equivalent dose limit from 150 to 20 mSv per year. This paper presents mainly the dose estimations received by industrial gamma radiography workers, during planned or accidental exposure to the eye lens, Hp(10) and effective dose. A Brazilian Visual Monte Carlo Dose Calculation program was used and two relevant scenarios were considered. For the planned exposure situation, twelve radiographic exposures per day for 250 days per year, which leads to a direct exposure of 10 h per year, were considered. The simulation was carried out using a Ir source with 1.0 TBq of activity; a source/operator distance between 5 and 10 m and placed at heights of 0.02 m, 1 m and 2 m, and an exposure time of 12 s. Using a standard height of 1 m, the eye lens doses were estimated as being between 16.3 and 60.3 mGy per year. For the accidental exposure situation, the same radionuclide and activity were used, but in this case the doses were calculated with and without a collimator. The heights above ground considered were 1.0 m, 1.5 m and 2.0 m; the source/operator distance was 40 cm, and the exposure time 74 s. The eye lens doses at 1.5 m were 12.3 and 0.28 mGy without and with a collimator, respectively. The conclusions were that: (1) the estimated doses show that the 20 mSv annual limit for eye lens equivalent dose can directly impact industrial gamma radiography activities, mainly in industries with high number of radiographic exposures per year; (2) the risk of lens opacity has a low probability for a single accident, but depending on the number of accidental exposures and the dose levels found in planned exposures, the threshold dose can easily be exceeded during the professional career of an industrial radiography operator, and; (3) in a first approximation, Hp(10) can be used to estimate the equivalent dose to the eye lens.
国际放射防护委员会（ICRP）的《组织反应声明》（2011年）基于流行病学证据，建议将眼晶状体当量剂量限值从每年150毫希沃特降至20毫希沃特。本文主要介绍了工业γ射线探伤工作人员在计划照射或意外照射眼晶状体期间所接受的剂量估算、Hp(10)和有效剂量。使用了巴西视觉蒙特卡罗剂量计算程序，并考虑了两种相关场景。对于计划照射情况，考虑每年250天每天进行12次射线照相照射，这导致每年直接照射10小时。模拟使用了活度为1.0太贝克勒尔的铱源；源与操作人员的距离在5至10米之间，放置高度为0.02米、1米和2米，照射时间为12秒。使用1米的标准高度，估算出每年眼晶状体剂量在16.3至60.3毫戈瑞之间。对于意外照射情况，使用了相同的放射性核素和活度，但在这种情况下，分别计算了有无准直器时的剂量。考虑的地面以上高度为1.0米、1.5米和2.0米；源与操作人员的距离为40厘米，照射时间为74秒。在1.5米高度处，无准直器和有准直器时的眼晶状体剂量分别为12.3毫戈瑞和0.28毫戈瑞。结论如下：（1）估算剂量表明，眼晶状体当量剂量每年20毫希沃特的限值会直接影响工业γ射线探伤活动，主要是在每年射线照相照射次数较多的行业；（2）单次事故导致晶状体混浊的风险概率较低，但取决于意外照射次数和计划照射中发现的剂量水平，在工业射线探伤操作人员的职业生涯中，很容易超过阈剂量；（3）初步估算时，Hp(10)可用于估算眼晶状体的当量剂量。
