怀孕病人的医疗辐射暴露:喀麦隆杜阿拉妇产科和儿科医院个案研究

A. Simó, Ateba Jfb, Manyol En, Ndah Tn, Ndontchueng Mm, Njiki Cd
{"title":"怀孕病人的医疗辐射暴露:喀麦隆杜阿拉妇产科和儿科医院个案研究","authors":"A. Simó, Ateba Jfb, Manyol En, Ndah Tn, Ndontchueng Mm, Njiki Cd","doi":"10.15761/rdi.1000126","DOIUrl":null,"url":null,"abstract":"The use of X-Ray in medical radiology is always risky. In particular, when it comes to imaging pregnant women, the majority of foetus cells might be damaged. Despite all the requirements from international renowned organizations relating to imaging of pregnant women and newborns, the unintentional irradiations of the foetus are still common in radiology services. A case that occurred at the Gynaeco Obstetric and Paediatric Hospital of Douala (Cameroon) in September 2015, is instructive. A 46-year-old woman about six months pregnant was subject to an X-Ray of the pelvis requested by a medical doctor following a suspicion “of osteonecrosis”. Investigations have been conducted by the National Radiation Protection Agency (NRPA) by using Diavolt kVp meter. In addition, theoretical foetal dose estimation has been proceeded to evaluate accuracy of the technical estimation of the obtained result. The patient was irradiated with parameters of 20 mAs and 90 kV which lead to a dose to foetus of about 213 μGy. The lead apron that was used to protect the pelvis reduced the absorbed dose by a factor of 6. The hospital officials were advised to do more collaboration between referral medical doctors and radiologists as soon as the use of X-Ray on pregnant women is deemed necessary, to inform patients about the dangers of ionizing radiation on foetus, and to request information on their pregnancy status as well. Correspondence to: Beyala Ateba JF, National Radiation Protection Agency of Cameroon, Yaoundé, Cameroon, E-mail: bajeanfelix@yahoo.fr Received: March 03, 2018; Accepted: March 20, 2018; Published: March 24, 2018 Introduction The use of X-ray generators for diagnostic radiology in the medical sector in Cameroon, Central Africa, is wide spread and on the increase in recent times [1]. One of the most commonly asked questions in relation to the use of ionizing radiation in medicine concerns the management of the pregnant patient. Instinctively, one might want to avoid use of radiation with a pregnant patient; however, there are a number of situations in which the use of radiation for diagnosis or therapy is appropriate. In addition, there are many female physicians and technicians who are employed in medical settings involving radiation. Thousands of pregnant patients and radiation workers are exposed to ionizing radiation each year [2]. X rays have also been used for more than 50 years to assess the dimensions of the maternal pelvis in pregnancy [3]. For occupationally exposed pregnant women, the equivalent dose to the surface of the abdomen shall not exceed 2 mSv per year and the effective dose resulting from exposure shall not exceed 1 mSv from the time which the pregnancy is known until its term [4,5]. According to presidential decree N° 2002/250, issued on 31st October 2002, National Radiation Protection Agency (NRPA), was established as the only Regulatory Body in Cameroon [6]. It is the competent authority for radiation protection and waste management issues. In this frame, the NRPA authorizes and controls the use of ionizing radiation sources to protect people and the environment against the harmful effects of radiation. Since the Decree N° 2002/250 states in article 4 (5) that, the NRPA is responsible to respond to radiological accident/incident, it has been notified of the radiological incident related to the irradiation of the fetus with X-ray machine occurred at the Gynaeco Obstetric and Paediatric Hospital of Douala, Cameroon. According to this notification, NRPA team carried out an investigation mission for estimating the dose to the fetus. This paper gives operational measures of management of the concerned incident. These measures will be shared in the whole medical sector in Cameroon to avoid similar cases. Material and method Management of a pregnant patient According to ICRP publication 84, NRPA has put in place some measures to manage pregnant patients in diagnostic radiology. Before X-ray examination, it should be determined whether a patient is, or may be, pregnant and whether the fetus will be in the direct beam. In addition, advisory notices should be posted at several places within diagnostic X-ray departments and areas where diagnostic X-ray equipment is used to avoid unintentional radiation exposures of the embryo and fetus. When a patient has been determined to be pregnant or possibly pregnant, the radiologist usually begins by determining whether the fetus is going to be in the primary X-ray beam. If not, then the risk to the fetus is extremely low and the most important thing is to keep the number and type of exposures to a minimum while still getting the correct diagnosis. When an examination is indicated in which the X-ray beam irradiates the fetus directly, and this cannot be delayed until after Simo A (2018) Medical radiation exposure of pregnant patients: case study of the gynaeco obstetric and paediatric hospital of douala, cameroon Volume 2(2): 2-4 Radiol Diagn Imaging, 2018 doi: 10.15761/RDI.1000126 pregnancy, the most common ways to tailor examinations and reduce fetal exposure are to collimate the beam to a very specific area of interest. When a high-dose procedure is performed and when the fetus is known to be in the primary X-ray beam, the technical factors should be recorded to allow subsequent fetal dose estimation. Experimental fetal dose estimation The NRPA investigation protocol has been used to measure entrance skin dose (ESD) of the pregnant woman. According to Mahadevappa in 2011, foetal dose be conservatively estimated as 0.15 times the entrance skin dose (ESD) for conventional radiography and fluoroscopy techniques [7]. DIAVOLT kVp-meter which is non-invasive kVp, PPV, dose and time meter for acceptance tests and quality control (QC) of diagnostic X-ray equipment has been used for the measurements. According to the NRPA Guidance N°0050 (2016) on quality control of X-ray machine in diagnostic radiology, steps given below were followed [8]. Mode RAD/FLU has been chosen; kVp ranged from 40 to 150 kV has been setted; filtration of 2.5 mmAl as indicated on the tube has been chosen; DIAVOLT kVp meter was positioned on the top of table at 100 cm of X-ray tube; light field was collimated on the size of the DIAVOLT; 20mAs and 90 kV have been chosen for tests; three measures of ESD have been recorded. The DIAVOLT kVp meter was covered by a lead apron of 0.25 mmPb to reproduce conditions of the examination for which physical parameters are given below: Source to image receptor distance is 1meter; Tube potential setting is 90 kV; Tube current setting 200 mA; Exposure time 0.1 second; Beam size: 43 cm x 35.5 cm; Patient AP thickness is 26 cm; Total filtration 2.5 mmAl. Theoretical fetal dose estimation An accurate approach to provide an estimation of fetal dose, either prospectively or retrospectively is to assess the dose for the individual patient using the technique parameters that were used for the patient’s examination and taking into account both fetal depth and size [9]. Specific values for the following parameters were requested: projection and view for each examination, filtration, source-to-imager receptor distance, machine outputs, and techniques parameters (kVp, tube current, exposure time, etc.) used for the examination(s). According to the NCRP report 54, the basic information that is required to estimate the dose to the embryo-fetus from radiographic examinations is the air exposure rate at some reference point and the half-value layer (HVL) [10]. The estimated exposure rate in air (mR/mAs) as a function of kVp and total aluminum filtration at 1 meter from the x-ray source can be obtained from Schulz and Gignac data (1976) for three phase equipment [11]. If the total filtration is known, the HVL may be estimated from NCRP report 33 published in 1968, for three phase and constant potential equipment [12]. The exposure rate in air can be determined at the source-skin distance (SSD) used by inverse square extrapolation. Result and discussion Table 1 shows doses measured by Diavolt kVp meter with lead apron on it. The mean value of about 1420 μGy was obtained. This value has been used to estimate a fetal absorbed dose which is found to be 213 μGy according to Mahadevappa in 2011. Effectiveness of the shielding enclosed in lead apron has been appreciated through ratio between doses measured by Diavolt without and cover with lead apron. Therefore, the shielding used to cover the pelvic attenuated the direct beam by a factor of about 6. According to the data collected from Schulz and Gignac curve on exposure rate in air at 1 m from the X-ray source and following data from NCRP report 33 where HVL is estimated as a function of tube potential for three phase generators, table 2 has been obtained by taking into account characteristics of x-ray source (Table 3) and exposure parameters. Total exposure at 1 m is given by the following relation: Total Exposure at 1m (mR) = courant (mAs) × numberofexposure mR × exposure rate in air ( ) mAs (1) Exposure in air at the source skin distance (SSD) is given by: 2 Total Exposure at 1 m Exposure in air at the SSD= SSD (2) In addition, the dose to the uterus per roentgen exposure at the skin has been estimated through the dose to the uterus for 1 roentgen entrance skin exposure from Rosenstein (1976) data reported by NCRP report 54 [13]. According to the above-mentioned procedure, the theoretical dose to the uterus has been found to be 1.8 mGy. Since the lead apron used for the exam reduced the absorbed dose by a factor of 6, it can be assumed that the received fetal dose will be approximately 300 μGy. Theoretical fetal dose estimation has been proceeded to evaluate accuracy of the experimental fetal dose estimation. The results are tabulated in table 4 together with those obtained theoretically. The fetal dose estimated is in agreement within 29%. According to ICRP 84, Estimation of the absorbed dose to the embryo or fetus from plain film ab","PeriodicalId":11275,"journal":{"name":"Diagnostic imaging","volume":"269 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2018-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Medical radiation exposure of pregnant patients: case study of the gynaeco obstetric and paediatric hospital of douala, cameroon\",\"authors\":\"A. Simó, Ateba Jfb, Manyol En, Ndah Tn, Ndontchueng Mm, Njiki Cd\",\"doi\":\"10.15761/rdi.1000126\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"The use of X-Ray in medical radiology is always risky. In particular, when it comes to imaging pregnant women, the majority of foetus cells might be damaged. Despite all the requirements from international renowned organizations relating to imaging of pregnant women and newborns, the unintentional irradiations of the foetus are still common in radiology services. A case that occurred at the Gynaeco Obstetric and Paediatric Hospital of Douala (Cameroon) in September 2015, is instructive. A 46-year-old woman about six months pregnant was subject to an X-Ray of the pelvis requested by a medical doctor following a suspicion “of osteonecrosis”. Investigations have been conducted by the National Radiation Protection Agency (NRPA) by using Diavolt kVp meter. In addition, theoretical foetal dose estimation has been proceeded to evaluate accuracy of the technical estimation of the obtained result. The patient was irradiated with parameters of 20 mAs and 90 kV which lead to a dose to foetus of about 213 μGy. The lead apron that was used to protect the pelvis reduced the absorbed dose by a factor of 6. The hospital officials were advised to do more collaboration between referral medical doctors and radiologists as soon as the use of X-Ray on pregnant women is deemed necessary, to inform patients about the dangers of ionizing radiation on foetus, and to request information on their pregnancy status as well. Correspondence to: Beyala Ateba JF, National Radiation Protection Agency of Cameroon, Yaoundé, Cameroon, E-mail: bajeanfelix@yahoo.fr Received: March 03, 2018; Accepted: March 20, 2018; Published: March 24, 2018 Introduction The use of X-ray generators for diagnostic radiology in the medical sector in Cameroon, Central Africa, is wide spread and on the increase in recent times [1]. One of the most commonly asked questions in relation to the use of ionizing radiation in medicine concerns the management of the pregnant patient. Instinctively, one might want to avoid use of radiation with a pregnant patient; however, there are a number of situations in which the use of radiation for diagnosis or therapy is appropriate. In addition, there are many female physicians and technicians who are employed in medical settings involving radiation. Thousands of pregnant patients and radiation workers are exposed to ionizing radiation each year [2]. X rays have also been used for more than 50 years to assess the dimensions of the maternal pelvis in pregnancy [3]. For occupationally exposed pregnant women, the equivalent dose to the surface of the abdomen shall not exceed 2 mSv per year and the effective dose resulting from exposure shall not exceed 1 mSv from the time which the pregnancy is known until its term [4,5]. According to presidential decree N° 2002/250, issued on 31st October 2002, National Radiation Protection Agency (NRPA), was established as the only Regulatory Body in Cameroon [6]. It is the competent authority for radiation protection and waste management issues. In this frame, the NRPA authorizes and controls the use of ionizing radiation sources to protect people and the environment against the harmful effects of radiation. Since the Decree N° 2002/250 states in article 4 (5) that, the NRPA is responsible to respond to radiological accident/incident, it has been notified of the radiological incident related to the irradiation of the fetus with X-ray machine occurred at the Gynaeco Obstetric and Paediatric Hospital of Douala, Cameroon. According to this notification, NRPA team carried out an investigation mission for estimating the dose to the fetus. This paper gives operational measures of management of the concerned incident. These measures will be shared in the whole medical sector in Cameroon to avoid similar cases. Material and method Management of a pregnant patient According to ICRP publication 84, NRPA has put in place some measures to manage pregnant patients in diagnostic radiology. Before X-ray examination, it should be determined whether a patient is, or may be, pregnant and whether the fetus will be in the direct beam. In addition, advisory notices should be posted at several places within diagnostic X-ray departments and areas where diagnostic X-ray equipment is used to avoid unintentional radiation exposures of the embryo and fetus. When a patient has been determined to be pregnant or possibly pregnant, the radiologist usually begins by determining whether the fetus is going to be in the primary X-ray beam. If not, then the risk to the fetus is extremely low and the most important thing is to keep the number and type of exposures to a minimum while still getting the correct diagnosis. When an examination is indicated in which the X-ray beam irradiates the fetus directly, and this cannot be delayed until after Simo A (2018) Medical radiation exposure of pregnant patients: case study of the gynaeco obstetric and paediatric hospital of douala, cameroon Volume 2(2): 2-4 Radiol Diagn Imaging, 2018 doi: 10.15761/RDI.1000126 pregnancy, the most common ways to tailor examinations and reduce fetal exposure are to collimate the beam to a very specific area of interest. When a high-dose procedure is performed and when the fetus is known to be in the primary X-ray beam, the technical factors should be recorded to allow subsequent fetal dose estimation. Experimental fetal dose estimation The NRPA investigation protocol has been used to measure entrance skin dose (ESD) of the pregnant woman. According to Mahadevappa in 2011, foetal dose be conservatively estimated as 0.15 times the entrance skin dose (ESD) for conventional radiography and fluoroscopy techniques [7]. DIAVOLT kVp-meter which is non-invasive kVp, PPV, dose and time meter for acceptance tests and quality control (QC) of diagnostic X-ray equipment has been used for the measurements. According to the NRPA Guidance N°0050 (2016) on quality control of X-ray machine in diagnostic radiology, steps given below were followed [8]. Mode RAD/FLU has been chosen; kVp ranged from 40 to 150 kV has been setted; filtration of 2.5 mmAl as indicated on the tube has been chosen; DIAVOLT kVp meter was positioned on the top of table at 100 cm of X-ray tube; light field was collimated on the size of the DIAVOLT; 20mAs and 90 kV have been chosen for tests; three measures of ESD have been recorded. The DIAVOLT kVp meter was covered by a lead apron of 0.25 mmPb to reproduce conditions of the examination for which physical parameters are given below: Source to image receptor distance is 1meter; Tube potential setting is 90 kV; Tube current setting 200 mA; Exposure time 0.1 second; Beam size: 43 cm x 35.5 cm; Patient AP thickness is 26 cm; Total filtration 2.5 mmAl. Theoretical fetal dose estimation An accurate approach to provide an estimation of fetal dose, either prospectively or retrospectively is to assess the dose for the individual patient using the technique parameters that were used for the patient’s examination and taking into account both fetal depth and size [9]. Specific values for the following parameters were requested: projection and view for each examination, filtration, source-to-imager receptor distance, machine outputs, and techniques parameters (kVp, tube current, exposure time, etc.) used for the examination(s). According to the NCRP report 54, the basic information that is required to estimate the dose to the embryo-fetus from radiographic examinations is the air exposure rate at some reference point and the half-value layer (HVL) [10]. The estimated exposure rate in air (mR/mAs) as a function of kVp and total aluminum filtration at 1 meter from the x-ray source can be obtained from Schulz and Gignac data (1976) for three phase equipment [11]. If the total filtration is known, the HVL may be estimated from NCRP report 33 published in 1968, for three phase and constant potential equipment [12]. The exposure rate in air can be determined at the source-skin distance (SSD) used by inverse square extrapolation. Result and discussion Table 1 shows doses measured by Diavolt kVp meter with lead apron on it. The mean value of about 1420 μGy was obtained. This value has been used to estimate a fetal absorbed dose which is found to be 213 μGy according to Mahadevappa in 2011. Effectiveness of the shielding enclosed in lead apron has been appreciated through ratio between doses measured by Diavolt without and cover with lead apron. Therefore, the shielding used to cover the pelvic attenuated the direct beam by a factor of about 6. According to the data collected from Schulz and Gignac curve on exposure rate in air at 1 m from the X-ray source and following data from NCRP report 33 where HVL is estimated as a function of tube potential for three phase generators, table 2 has been obtained by taking into account characteristics of x-ray source (Table 3) and exposure parameters. Total exposure at 1 m is given by the following relation: Total Exposure at 1m (mR) = courant (mAs) × numberofexposure mR × exposure rate in air ( ) mAs (1) Exposure in air at the source skin distance (SSD) is given by: 2 Total Exposure at 1 m Exposure in air at the SSD= SSD (2) In addition, the dose to the uterus per roentgen exposure at the skin has been estimated through the dose to the uterus for 1 roentgen entrance skin exposure from Rosenstein (1976) data reported by NCRP report 54 [13]. According to the above-mentioned procedure, the theoretical dose to the uterus has been found to be 1.8 mGy. Since the lead apron used for the exam reduced the absorbed dose by a factor of 6, it can be assumed that the received fetal dose will be approximately 300 μGy. Theoretical fetal dose estimation has been proceeded to evaluate accuracy of the experimental fetal dose estimation. The results are tabulated in table 4 together with those obtained theoretically. The fetal dose estimated is in agreement within 29%. 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摘要

在医学放射学中使用x射线总是有风险的。特别是,当对孕妇进行成像时,大多数胎儿细胞可能会受损。尽管国际知名组织对孕妇和新生儿的成像有各种要求,但在放射学服务中,对胎儿的意外照射仍然很常见。2015年9月发生在杜阿拉(喀麦隆)妇产科和儿科医院的一个病例具有指导意义。一名怀孕约6个月的46岁妇女因怀疑"骨坏死",在医生的要求下接受了骨盆x光检查。美国国家辐射防护署(NRPA)使用Diavolt kVp计进行了调查。此外,还进行了理论胎儿剂量估计,以评价所得结果的技术估计的准确性。患者接受20 ma和90 kV的辐照,对胎儿的辐照量约为213 μGy。用于保护骨盆的铅围裙将吸收剂量降低了6倍。建议医院官员在认为有必要对孕妇使用x射线时,在转诊医生和放射科医生之间进行更多的合作,告知患者电离辐射对胎儿的危险,并要求提供有关其怀孕状况的信息。通讯:Beyala Ateba JF,喀麦隆国家辐射防护机构,yaound<e:1>,喀麦隆,E-mail: bajeanfelix@yahoo.fr收稿日期:2018年03月03日;录用日期:2018年3月20日;简介在中非喀麦隆的医疗部门,x射线发生器用于诊断放射学的使用非常广泛,并且近年来呈上升趋势。关于在医学中使用电离辐射,最常被问到的问题之一是对怀孕病人的管理。出于本能,人们可能会想避免对孕妇使用辐射;然而,在一些情况下,使用辐射进行诊断或治疗是合适的。此外,还有许多女医生和技术人员受雇于涉及辐射的医疗机构。每年有成千上万的孕妇和辐射工作者暴露在电离辐射下。50多年来,X射线也被用于评估孕妇骨盆的尺寸。对于职业性暴露的孕妇,从知道怀孕到足月,每年腹部表面的等效剂量不应超过2毫西弗,暴露产生的有效剂量不应超过1毫西弗[4,5]。根据2002年10月31日发布的第2002/250号总统令,成立了国家辐射保护局(NRPA),作为喀麦隆唯一的监管机构。是主管辐射防护及废弃物管理之主管机关。在此框架下,NRPA授权并控制电离辐射源的使用,以保护人类和环境免受辐射的有害影响。自从第2002/250号法令第4(5)条规定国家原子能机构负责应对放射性事故/事件以来,它已经收到了喀麦隆杜阿拉妇产科和儿科医院发生的与x光机照射胎儿有关的放射性事件的通知。根据这一通知,NRPA小组开展了一项调查任务,以估计对胎儿的剂量。本文给出了相关事件管理的操作措施。这些措施将在喀麦隆整个医疗部门共享,以避免类似情况发生。根据ICRP第84号出版物,NRPA制定了一些措施来管理诊断放射学中的怀孕患者。在x线检查之前,应确定患者是否怀孕或可能怀孕,以及胎儿是否会在直射光束中。此外,应在x射线诊断部门和使用x射线诊断设备的区域内的几个地方张贴咨询通知,以避免胚胎和胎儿的无意辐射暴露。当一个病人被确定怀孕或可能怀孕时,放射科医生通常首先确定胎儿是否会出现在初级x射线束中。如果没有,那么胎儿的风险就极低,最重要的是在得到正确诊断的同时,尽量减少接触的次数和类型。当检查表明x射线束直接照射胎儿时,这不能推迟到Simo A(2018年)怀孕患者的医疗辐射暴露:喀麦隆杜阿拉妇产科和儿科医院的案例研究第2卷(2):2-4放射诊断成像,2018年doi: 10。 15761 / RDI。1000126怀孕,最常见的方法来定制检查和减少胎儿暴露是准直光束到一个非常具体的兴趣区域。当进行高剂量手术时,当已知胎儿处于主x射线束中时,应记录技术因素,以便随后对胎儿剂量进行估计。实验胎儿剂量估计采用NRPA调查方案测量孕妇皮肤入口剂量(ESD)。根据Mahadevappa 2011年的研究,保守估计胎儿剂量为常规x线摄影和透视技术的入口皮肤剂量(ESD)的0.15倍。DIAVOLT kVp-meter是用于x射线诊断设备验收测试和质量控制(QC)的无创kVp, PPV,剂量和时间计。根据NRPA指南N°0050(2016)关于诊断放射学x光机质量控制的要求,遵循以下步骤。已选择RAD/FLU模式;kVp设定范围为40 ~ 150kv;已选择滤管上显示的2.5 mmAl过滤;DIAVOLT kVp计放置在工作台顶部距x射线管100 cm处;光场对准DIAVOLT的大小;试验选用20ma和90kv;记录了三个ESD测量值。DIAVOLT kVp计被0.25 mmPb的铅圈覆盖,以再现检查条件,其物理参数如下:源到图像受体的距离为1米;管电位设定为90kv;管电流设定200ma;曝光时间0.1秒;梁尺寸:43厘米x 35.5厘米;患者AP厚度26 cm;总过滤2.5毫摩尔。理论胎儿剂量估计提供胎儿剂量估计的准确方法,无论是前瞻性的还是回顾性的,都是使用用于患者检查的技术参数并考虑胎儿深度和大小bbb来评估个体患者的剂量。要求以下参数的具体值:每次检查的投影和视图,过滤,源到成像仪受体的距离,机器输出,以及用于检查的技术参数(kVp,管电流,曝光时间等)。根据NCRP报告54,估计放射检查对胚胎-胎儿的剂量所需的基本信息是某参考点的空气暴露率和半值层(HVL)[10]。从Schulz和Gignac(1976)的三相设备[11]的数据中可以得到空气中估计的暴露率(mR/mAs)作为距离x射线源1米处kVp和总铝过滤的函数。如果总过滤是已知的,则可以从1968年发表的NCRP报告33中估计三相和恒电位设备[12]的HVL。空气中的暴露率可以用平方反比外推法在源肤距离(SSD)上确定。表1显示了用带铅圈的diavt kVp计测量的剂量。其平均值约为1420 μGy。这个值被用来估计胎儿吸收剂量,根据Mahadevappa在2011年发现的213 μGy。通过无铅围圈和有铅围圈的Diavolt测量的剂量之比,对铅围圈的屏蔽效果进行了评价。因此,用于覆盖骨盆的屏蔽将直接光束衰减了约6倍。根据距离x射线源1m处空气中暴露率的Schulz和Gignac曲线收集的数据,以及NCRP报告33中HVL作为三相发生器管电位的函数估计的数据,考虑x射线源的特性(表3)和暴露参数,得到表2。总暴露在1米是由以下关系:总暴露在1 m(先生)=报(mAs)××先生numberofexposure曝光率在空气中()mAs(1)暴露在空气源(SSD)是由皮肤距离:2总暴露在1 m暴露在空气SSD = SSD(2)此外,子宫的剂量每伦琴暴露皮肤据估计通过剂量子宫1伦琴入口的皮肤接触Rosenstein(1976)数据报告摘要NCRP 54[13]。根据上述程序,已发现子宫的理论剂量为1.8毫戈瑞。由于用于检查的铅围裙将吸收剂量降低了6倍,因此可以假设胎儿接受的剂量约为300 μGy。对胎儿剂量进行了理论估计,以评价实验胎儿剂量估计的准确性。结果与理论所得结果列于表4。胎儿剂量估计值在29%以内一致。根据ICRP 84,胚胎或胎儿从普通膜吸收剂量的估计
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Medical radiation exposure of pregnant patients: case study of the gynaeco obstetric and paediatric hospital of douala, cameroon
The use of X-Ray in medical radiology is always risky. In particular, when it comes to imaging pregnant women, the majority of foetus cells might be damaged. Despite all the requirements from international renowned organizations relating to imaging of pregnant women and newborns, the unintentional irradiations of the foetus are still common in radiology services. A case that occurred at the Gynaeco Obstetric and Paediatric Hospital of Douala (Cameroon) in September 2015, is instructive. A 46-year-old woman about six months pregnant was subject to an X-Ray of the pelvis requested by a medical doctor following a suspicion “of osteonecrosis”. Investigations have been conducted by the National Radiation Protection Agency (NRPA) by using Diavolt kVp meter. In addition, theoretical foetal dose estimation has been proceeded to evaluate accuracy of the technical estimation of the obtained result. The patient was irradiated with parameters of 20 mAs and 90 kV which lead to a dose to foetus of about 213 μGy. The lead apron that was used to protect the pelvis reduced the absorbed dose by a factor of 6. The hospital officials were advised to do more collaboration between referral medical doctors and radiologists as soon as the use of X-Ray on pregnant women is deemed necessary, to inform patients about the dangers of ionizing radiation on foetus, and to request information on their pregnancy status as well. Correspondence to: Beyala Ateba JF, National Radiation Protection Agency of Cameroon, Yaoundé, Cameroon, E-mail: bajeanfelix@yahoo.fr Received: March 03, 2018; Accepted: March 20, 2018; Published: March 24, 2018 Introduction The use of X-ray generators for diagnostic radiology in the medical sector in Cameroon, Central Africa, is wide spread and on the increase in recent times [1]. One of the most commonly asked questions in relation to the use of ionizing radiation in medicine concerns the management of the pregnant patient. Instinctively, one might want to avoid use of radiation with a pregnant patient; however, there are a number of situations in which the use of radiation for diagnosis or therapy is appropriate. In addition, there are many female physicians and technicians who are employed in medical settings involving radiation. Thousands of pregnant patients and radiation workers are exposed to ionizing radiation each year [2]. X rays have also been used for more than 50 years to assess the dimensions of the maternal pelvis in pregnancy [3]. For occupationally exposed pregnant women, the equivalent dose to the surface of the abdomen shall not exceed 2 mSv per year and the effective dose resulting from exposure shall not exceed 1 mSv from the time which the pregnancy is known until its term [4,5]. According to presidential decree N° 2002/250, issued on 31st October 2002, National Radiation Protection Agency (NRPA), was established as the only Regulatory Body in Cameroon [6]. It is the competent authority for radiation protection and waste management issues. In this frame, the NRPA authorizes and controls the use of ionizing radiation sources to protect people and the environment against the harmful effects of radiation. Since the Decree N° 2002/250 states in article 4 (5) that, the NRPA is responsible to respond to radiological accident/incident, it has been notified of the radiological incident related to the irradiation of the fetus with X-ray machine occurred at the Gynaeco Obstetric and Paediatric Hospital of Douala, Cameroon. According to this notification, NRPA team carried out an investigation mission for estimating the dose to the fetus. This paper gives operational measures of management of the concerned incident. These measures will be shared in the whole medical sector in Cameroon to avoid similar cases. Material and method Management of a pregnant patient According to ICRP publication 84, NRPA has put in place some measures to manage pregnant patients in diagnostic radiology. Before X-ray examination, it should be determined whether a patient is, or may be, pregnant and whether the fetus will be in the direct beam. In addition, advisory notices should be posted at several places within diagnostic X-ray departments and areas where diagnostic X-ray equipment is used to avoid unintentional radiation exposures of the embryo and fetus. When a patient has been determined to be pregnant or possibly pregnant, the radiologist usually begins by determining whether the fetus is going to be in the primary X-ray beam. If not, then the risk to the fetus is extremely low and the most important thing is to keep the number and type of exposures to a minimum while still getting the correct diagnosis. When an examination is indicated in which the X-ray beam irradiates the fetus directly, and this cannot be delayed until after Simo A (2018) Medical radiation exposure of pregnant patients: case study of the gynaeco obstetric and paediatric hospital of douala, cameroon Volume 2(2): 2-4 Radiol Diagn Imaging, 2018 doi: 10.15761/RDI.1000126 pregnancy, the most common ways to tailor examinations and reduce fetal exposure are to collimate the beam to a very specific area of interest. When a high-dose procedure is performed and when the fetus is known to be in the primary X-ray beam, the technical factors should be recorded to allow subsequent fetal dose estimation. Experimental fetal dose estimation The NRPA investigation protocol has been used to measure entrance skin dose (ESD) of the pregnant woman. According to Mahadevappa in 2011, foetal dose be conservatively estimated as 0.15 times the entrance skin dose (ESD) for conventional radiography and fluoroscopy techniques [7]. DIAVOLT kVp-meter which is non-invasive kVp, PPV, dose and time meter for acceptance tests and quality control (QC) of diagnostic X-ray equipment has been used for the measurements. According to the NRPA Guidance N°0050 (2016) on quality control of X-ray machine in diagnostic radiology, steps given below were followed [8]. Mode RAD/FLU has been chosen; kVp ranged from 40 to 150 kV has been setted; filtration of 2.5 mmAl as indicated on the tube has been chosen; DIAVOLT kVp meter was positioned on the top of table at 100 cm of X-ray tube; light field was collimated on the size of the DIAVOLT; 20mAs and 90 kV have been chosen for tests; three measures of ESD have been recorded. The DIAVOLT kVp meter was covered by a lead apron of 0.25 mmPb to reproduce conditions of the examination for which physical parameters are given below: Source to image receptor distance is 1meter; Tube potential setting is 90 kV; Tube current setting 200 mA; Exposure time 0.1 second; Beam size: 43 cm x 35.5 cm; Patient AP thickness is 26 cm; Total filtration 2.5 mmAl. Theoretical fetal dose estimation An accurate approach to provide an estimation of fetal dose, either prospectively or retrospectively is to assess the dose for the individual patient using the technique parameters that were used for the patient’s examination and taking into account both fetal depth and size [9]. Specific values for the following parameters were requested: projection and view for each examination, filtration, source-to-imager receptor distance, machine outputs, and techniques parameters (kVp, tube current, exposure time, etc.) used for the examination(s). According to the NCRP report 54, the basic information that is required to estimate the dose to the embryo-fetus from radiographic examinations is the air exposure rate at some reference point and the half-value layer (HVL) [10]. The estimated exposure rate in air (mR/mAs) as a function of kVp and total aluminum filtration at 1 meter from the x-ray source can be obtained from Schulz and Gignac data (1976) for three phase equipment [11]. If the total filtration is known, the HVL may be estimated from NCRP report 33 published in 1968, for three phase and constant potential equipment [12]. The exposure rate in air can be determined at the source-skin distance (SSD) used by inverse square extrapolation. Result and discussion Table 1 shows doses measured by Diavolt kVp meter with lead apron on it. The mean value of about 1420 μGy was obtained. This value has been used to estimate a fetal absorbed dose which is found to be 213 μGy according to Mahadevappa in 2011. Effectiveness of the shielding enclosed in lead apron has been appreciated through ratio between doses measured by Diavolt without and cover with lead apron. Therefore, the shielding used to cover the pelvic attenuated the direct beam by a factor of about 6. According to the data collected from Schulz and Gignac curve on exposure rate in air at 1 m from the X-ray source and following data from NCRP report 33 where HVL is estimated as a function of tube potential for three phase generators, table 2 has been obtained by taking into account characteristics of x-ray source (Table 3) and exposure parameters. Total exposure at 1 m is given by the following relation: Total Exposure at 1m (mR) = courant (mAs) × numberofexposure mR × exposure rate in air ( ) mAs (1) Exposure in air at the source skin distance (SSD) is given by: 2 Total Exposure at 1 m Exposure in air at the SSD= SSD (2) In addition, the dose to the uterus per roentgen exposure at the skin has been estimated through the dose to the uterus for 1 roentgen entrance skin exposure from Rosenstein (1976) data reported by NCRP report 54 [13]. According to the above-mentioned procedure, the theoretical dose to the uterus has been found to be 1.8 mGy. Since the lead apron used for the exam reduced the absorbed dose by a factor of 6, it can be assumed that the received fetal dose will be approximately 300 μGy. Theoretical fetal dose estimation has been proceeded to evaluate accuracy of the experimental fetal dose estimation. The results are tabulated in table 4 together with those obtained theoretically. The fetal dose estimated is in agreement within 29%. According to ICRP 84, Estimation of the absorbed dose to the embryo or fetus from plain film ab
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