TY - JOUR
AU1 - Ateba, J F Beyala
AU2 - Sabouang, J F
AU3 - Simo, A
AU4 - Moyo, M
AU5 - Haieta, H
AB - Abstract Operational measures taken for the repatriation of Alcyon II 60Co Teletherapy head and El Dorado 6 60Co Teletherapy devices located in Yaounde and Douala respectively are reported. Operations carried out have permit to store Alcyon head in the CC 33 container and to transfer 60Co source from El Dorado 6 device to YKT1B container. These containers are approved as Type B package for securely transport. Optically stimulated luminescence dosimeters had been distributed to all involved persons to estimate the received effective dose during operations. It appears by the present study that, the most received individual effective dose is 130 μSv during the whole process. INTRODUCTION Sealed high activity radioactive sources (SHARS) include all of the industrial radiography, teletherapy equipment and irradiators(1). Teletherapy is the use of radioisotopes as a source of beams of gamma radiation for medical treatment. Teletherapy equipment usually consists of a teletherapy head mounted on a mechanism, which allows the position and orientation of the head to be adjusted in order to direct the radiation beam at the affected organ of the patient. The sealed source is mounted inside the teletherapy head, which usually contains several hundred kilograms of high density shielding material. The head incorporates a shutter mechanism and beam collimating system. The shield material may be lead, tungsten or depleted uranium, in a steel shell. Teletherapy equipment became available in 1951, and initially used 137Cs. This nuclide continued to be used through the 1960s, but was gradually superseded by 60Co for safety reasons(1). 1985 was the year of the beginning of radiotherapy in Cameroon with the acquisition of El dorado 60Co device by a private promoter of public health located in Douala. Given high cost of cancer care in the private sector, the government of Cameroon through technical cooperation with the International Atomic Energy Agency (IAEA) had opened two radiotherapy services with 02 Alcyon II 60Co devices in 1988(2). In general, the source change time of Alcyon II devices with 60Co is less or equal to 10 years(3). The Alcyon II Teletherapy head installed in Yaounde since 1995 which replaced the Alcyon head installed in 1988 and the El dorado device located in Douala were concerned by the repatriation. The El dorado 6 device was stored in a pit of 1.10 m depth, situated in the clinic garden considered as public area (Figure 1) with more than 10 μSv/h dose rate at 1 m above the pit. The Alcyon II device was stored in the bunker used as office after closing the radiotherapy department. Figure 1. View largeDownload slide Clinic garden El dorado device interim storage. Figure 1. View largeDownload slide Clinic garden El dorado device interim storage. Since Cameroon National Radiation Protection Agency (NRPA) has no centralized waste facility to decommission, manage and store category I 60Co teletherapy units, the IAEA which is not encouraged storage of SHARS at third party facility had been contacted for the support of the repatriation. This article describes the dismantling steps of each type of 60Co unit, and personal doses measured during the whole process conducted by a contractor chosen by IAEA. Operational activities in the field have been developed according to the IAEA safety standard to assure harmless and ecologically rational management of disused sealed radioactive sources (DSRS). MATERIAL AND METHOD Preliminary duties The contractor had performed necessary arrangements and preparatory work and applied for all licenses and authorizations necessary for the performance of Work and for the packaging and transportation of the DSRS. NRPA had issued all the requested authorizations and had put in place all mechanisms for the success of the mission according to the decree 2002/250 of 31st October 2002 on its creation, organization and functioning(4). Technical issues Operation in douala To protect public from exposure to ionizing radiation in the hospital, the El dorado 6 device was moved from the storage pit dug in the garden to a specific local with more than 25 m2 of surface and 3.5 m height in the Bedi district where the source was unloaded and transferred to the YKT1B container. Operation in Douala was realized in three important steps. The first one consisted in securing the source in the El dorado device and transporting the associated equipment from the clinic to the Bedi district local for its transfer in an appropriate Type B package. In fact, during interim storage of the device in the garden, the source was not at a safe position. The El Dorado comprises longitudinally a head, a foot and a jack which makes it possible to move the source door slide and to place it in the irradiation position or in the safe position. To move or transport the equipment, it was necessary first to lock the source door drawer with a visible circular interface mounted on the side of the equipment head. In the absence of locking, any inclination of the equipment which would lead to positioning the arm higher than the head causes the drawer to move and places the source in the irradiation position. A cylindrical metal rod was used to push the radioactive source back to the bottom of its cage as shown in Figure 2. A wipe test was carried out on the source support and leads to the conclusion of non-contamination. The contamination was measured using a hand held contamination monitor, model LB 124 SCINT from Berthold. 17 October 2016 is the last calibration date of the concerned contamination monitor which is supposed to be calibrated on 17 October 2017. The measured value which was 1 Bq/cm2 is less than the limit value of 4 Bq/cm2 from which contamination of source support may be suspected. The second step was the transfer of the 60Co source from the El Dorado device to the Type B package namely YKT1B. After this specific operation, the source drawer of the YKT1B container was closed and the ambient dose rates were measured. Since the contact dose rate was approximately equal to the background, the I-white label has been used for the transportation purpose. Thus the last step was the transport of the source contained in the Type B package as well as the empty El dorado 6 device from Bedi district to Douala International Airport. This transport was carried out under police escort to avoid traffic jam and to promote the implementation of security measures during itinerary. Figure 2. View largeDownload slide El dorado 6 device with cylindrical metal used to push the radioactive source back to the bottom of its cage. Figure 2. View largeDownload slide El dorado 6 device with cylindrical metal used to push the radioactive source back to the bottom of its cage. Operation in Yaounde The work of contractor consisted in dismantling Alcyon II machine, packing the head with 60Co source and depleted uranium contained in the collimator separately. This work was realized in four stages, namely: dismantling of Alcyon II equipment, transfer of the head with its source towards the CC 33 container, packing of depleted uranium in an appropriate transport box and labeling of packages. First of all, electrical power alimentation of the machine was shut down. The dismantling procedure of alcyon II device has been followed according to Yasser Tawflk Selim et al. in 2013(5). The main precaution taken for the dismantling of Alcyon II head containing 60Co source consisted in putting the source in a safe position in order to avoid any movement during transport. In fact, the source is in the form of a cylindrical tube and is mounted on a device which can perform rotational movements. Three safety devices have been mounted, one allows the shutter to be locked, and the other two preventing any rotational movement of the source. The other important precaution was to prevent unbalance when the head was removed. This was achieved by using a stopper stick in the back which prevents the rotation of the machine due to the weight balance. At the end of the disassembly of the Alcyon II head, a wipe test was performed at the orifice of the Alcyon II head in order to check any surface contamination. This was done by using a hand held contamination monitor from Berthold. The measured value was 0.11 Bq/cm2. Labeling was an essential step for the transportation of radioactive and nuclear materials. It gives information on the contents of the packaging, as well as the intensity of radiation in contact and at 1 m from the package. At the contact of the CC 33 container dose rate was approximately equal to the background, the I-white label was pasted on the package for the transportation purpose. Description of CC 33 and YKT1B containers Description of CC 33 container According to France Nuclear Safety Authority certificate of approval F/370/B(U)-96 Ek(6), The CC 33 transportation Container (Figure 3) consists of a cylindrical packaging with a vertical axis, made of X2CrNi 18-9 stainless steel and 8 mm thick, entirely padded with a cork layer with a thickness of 10 mm. Figure 3. View largeDownload slide Diagram of alcyon II head packed in a CC 33 container. Figure 3. View largeDownload slide Diagram of alcyon II head packed in a CC 33 container. The CC 33 cask consists of two half shells: – The container, with a flat-bottomed cylindrical shape, a height of 946 mm and equipped with skid pallets screwed to its base. – The cover, with a flat-bottomed cylindrical shape, of height 354 mm and fitted with four lifting flanges, made of X2CrNi 18-9 stainless steel and 8 mm thick is welded on each half shell. Characteristics of 60Co source contains in the Alcyon II head device packed in a CC 33 container are given in Table 1. Table 1. Characteristics of Co-60 source in Alcyon II device. Manufacturer  Nuclide  Type  Serial no.  Activity (Ci)  Date of measurement  Physical form  Status  CIS Bio International  Co-60  COT20  3860  5 503.817  06/02/1995  Solid  Rapatriated  Manufacturer  Nuclide  Type  Serial no.  Activity (Ci)  Date of measurement  Physical form  Status  CIS Bio International  Co-60  COT20  3860  5 503.817  06/02/1995  Solid  Rapatriated  Description of YKT1B container According to IAEA TECDOC 1424 published in 2004 on directory of national competent authorities’ approval certificates for package design, special form material and shipment of radioactive material, the YKT1B transportation Container consists of a cylindrical packaging with a vertical axis, made of steel and lead with security tare. Following the State Atomic Energy Corporation Rosatom certificate of approval(6), YKT1B consists (Figure 4) of shielding container, Protective container and shock absorbers. Figure 4. View largeDownload slide Packaging set transportation YKT1B(U). Figure 4. View largeDownload slide Packaging set transportation YKT1B(U). Shielding container (Figure 5) is designed to decrease the intensity of a gamma radiation dose and to ensure impermeability of the packaging set. Figure 5. View largeDownload slide Shielding container. Figure 5. View largeDownload slide Shielding container. Protective container is designed to protect shielding container against mechanical damages, loss of sources, decreasing temperature loads both under normal operation conditions and in case any incidents occur. The shock absorbers are design elements ensuring fixation of the shielding container inside the protective container and reducing dynamic loads on it. Characteristics of 60Co source contained in the El dorado device and which was transferred and packed in a YKT1B container are given in Table 2. Table 2. Characteristics of Co-60 source in El dorado 6 device. Manufacturer  Nuclide  Type  Serial no.  Exposition rate at 1 m (R/h)  Reference date  Physical form  Status  (CEA)  Co-60  COT20  3271  2130  13/09/1985  Solid  Rapatriated  Manufacturer  Nuclide  Type  Serial no.  Exposition rate at 1 m (R/h)  Reference date  Physical form  Status  (CEA)  Co-60  COT20  3271  2130  13/09/1985  Solid  Rapatriated  Estimation of exposure dose from the involved persons During operations, NRPA carried out individual dosimetry monitoring of international experts and other involved persons. OSL dosimeters have been used to perform individual dosimetry of workers under ionizing radiation during the whole process. Low radiation dose of 0.05 mSv can be measured with OSL dosimeter that was used to control effective dose received by each exposed person. Another advantage of OSL technology is the possibility of proofreading. A total of 24 dosimeters were distributed to workers. These dosimeters were collected at the end of operations and the exposure radiation dose of each involved person was measured and recorded. Individual effective dose received by each involved person during the repatriation operation is reported in Table 4. RESULTS AND DISCUSSION During the whole process, measurements of dose rates were performed by using a radiagem dose rates survey meter to control the radiological exposition of workers and public. These measures which are presented in the Table 3 were performed at the beginning of the operation until the time when the source was introduced into the appropriate package for transport. The maximum dose rate was recorded at the outlet of collimator before the disassembly of the alcyon II head and the El dorado device respectively. The measured dose rates allow on to have the status of sources in the devices. According to the Table 3, measurements around devices have led to the conclusion that 60Co source in the alcyon II head was at the safe position, while the disused sealed 60Co source contained in the El dorado device was not at a safe position. The dismantling process and the transfer of El dorado device from its bunker to the interim storage in the clinic garden have not been done according to the IAEA safety standard. In parallel, the wipe test performed at the orifice of the devices reveals that any source leakage has not take place. According to the transport regulation from IAEA(7), any contamination on the external surfaces shall be kept as low as practicable and, under routine conditions of transport, shall not exceed 4 Bq/cm2 for beta and gamma emitters. Table 3. Dose rates measured before operations. Measurement point  Dose rates (μSv/h)  El Dorado device  Alcyon II device  In contact of collimator  671  42  Opposite side of collimator  99.20  10.70  At 1 m of the source  10  0.15  Measurement point  Dose rates (μSv/h)  El Dorado device  Alcyon II device  In contact of collimator  671  42  Opposite side of collimator  99.20  10.70  At 1 m of the source  10  0.15  According to individual dosimetry, the regulatory limit for annual dose is 20 mSv for workers under ionizing radiation. But in order to optimize the protection of relevant workers, the NRPA does carry out investigation when the personal dose equivalent during 1 month exceeds 1.5 mSv(8). Doses of involved persons measured during the repatriation of Alcyon II 60Co Teletherapy head and El Dorado 6 60Co Teletherapy device are given in Table 4. The lowest individual dose equivalent measured was 0.050 mSv, while the greatest value was 0.130 mSv. The radiation dose received by each personnel from Police and General Hospital of Yaounde is lower or equal to 0.050 mSv. The radiation dose received by each staff of NRPA is ranged between 0.070 and 0.100 mSv. The greatest effective dose measured of 0.130 mSv was received by the experts involved in the operation. In conclusion, only staff of NRPA and experts have received effective dose as workers under ionizing radiation. The radiation dose received by each one of these personnel is lower than the monthly limit of 1.5 mSv leading to investigations by NRPA. Since the operation in Douala has not taken place in the clinic, a personnel involved was not exposed to ionizing radiation during the operation. Table 4. Involved person's dosimetry. N  Dosimeter ID  Hp(10)  Hp(0.03)  Hp(0.07)  Involved person  1  XA018415577  ISEa  ISE  ISE  NRPA staffs  2  XA018415585  0.08  0.08  0.07  3  XA01842988T  0.07  0.07  0.07  4  XA018429916  0.09  0.09  0.08  5  XA018431789  0.10  0.10  0.09  6  XA01860525B  0.07  0.07  0.07  7  XA01860749X  ISE  ISE  ISE  8  XA029782460  ISE  ISE  ISE  9  XA029782618  0.07  0.07  0.07  10  XA029783244  ISE  ISE  ISE  11  XA029785703  ISE  ISE  ISE  12  XA02978838L  0.07  0.07  0.07  13  XA01842067F  0.07  0.07  0.07  International experts staffs  14  XA018428158  0.13  0.13  0.12  15  XA01843218D  0.09  0.09  0.09  16  XA02978745S  0.08  0.08  0.07  17  XA02978862U  0.08  0.08  0.08  18  XA01841760G  0.08  0.08  0.08  Yaounde General Hospital staffs  19  XA018417755  0.05  0.05  0.05  20  XA02978869G  0.05  0.05  ISE  21  XA01843165G  0.05  0.05  0.05  Police staff  22  XA029785612  ISE  ISE  ISE  23  XA029783327  ISE  ISE  ISE  Transportation staff  24  XA01843039D  0.06  0.06  0.05  N  Dosimeter ID  Hp(10)  Hp(0.03)  Hp(0.07)  Involved person  1  XA018415577  ISEa  ISE  ISE  NRPA staffs  2  XA018415585  0.08  0.08  0.07  3  XA01842988T  0.07  0.07  0.07  4  XA018429916  0.09  0.09  0.08  5  XA018431789  0.10  0.10  0.09  6  XA01860525B  0.07  0.07  0.07  7  XA01860749X  ISE  ISE  ISE  8  XA029782460  ISE  ISE  ISE  9  XA029782618  0.07  0.07  0.07  10  XA029783244  ISE  ISE  ISE  11  XA029785703  ISE  ISE  ISE  12  XA02978838L  0.07  0.07  0.07  13  XA01842067F  0.07  0.07  0.07  International experts staffs  14  XA018428158  0.13  0.13  0.12  15  XA01843218D  0.09  0.09  0.09  16  XA02978745S  0.08  0.08  0.07  17  XA02978862U  0.08  0.08  0.08  18  XA01841760G  0.08  0.08  0.08  Yaounde General Hospital staffs  19  XA018417755  0.05  0.05  0.05  20  XA02978869G  0.05  0.05  ISE  21  XA01843165G  0.05  0.05  0.05  Police staff  22  XA029785612  ISE  ISE  ISE  23  XA029783327  ISE  ISE  ISE  Transportation staff  24  XA01843039D  0.06  0.06  0.05  aMeasurement less than detection limit. CONCLUSION Dismantling of SHARS was realized in Cameroon under the NRPA coordination. These operations were done following IAEA safety standards. Since wipe tests have not revealed contamination of source supports, the main risks during the process were mechanical issues and exposition of peoples. The radiation dose received by individuals involved in the operation was evaluated using OSL dosimeters. The greatest individual effective dose received during the whole process was 0.130 mSv. Unfortunately the work performed by owner of the El dorado device in Douala, which has consisted to transfer the machine from the clinic to the interim storage in the garden, has not been done according to IAEA safety standards. FUNDING This work was supported by extra budgetary contribution in the framework of the Technical Cooperation Project CMR/9/005. ACKNOWLEDGMENTS The authors thank IAEA for their continuous efforts and technical guidance during this work. REFERENCES 1 International Atomic Energy Agency. Management of spent high activity radioactive sources (SHARS). IAEA TECDOC 1301 (2002). 2 Mouele Sone, A. and Yomi, J. Introduction de la radiothérapie dans un pays en voie de développement: l'exemple du Cameroun. Méd. Afr. Noire  37( 3), 94– 97 ( 1990). 3 Malik, S. R., Rahman, M., Mia, M., Jobber, A., Ashish, K., Bairagi, S. R., Ahmed, M. and Yeasmin, N. Comprehensive benchmark procedures for commissioning: quality assurance and treatment delivery for quality cancer therapy using Co-60 teletherapy machine. Bangladesh J. Med. Phys.  6( 1), 3– 20 ( 2013). 4 Decree, N. 2002/250 of 31 October 2002 to set up, organize and regulate the functioning of the National Radiation Protection Agency. Official Gazette of the republic of Cameroon (2003). 5 Yasser Tawflk Selim, T., Lasheen, Y. F., Hassan, M. A. and Zakla, T. M. E. Removal of Alcyon II, CGR, MeV 60Co teletherapy head and evaluation of exposure dose. J. Environ. Prot.  4, 1435– 1440 ( 2013). Google Scholar CrossRef Search ADS   6 International Atomic Energy Agency. Directory of national competent authorities’ approval certificates for package design, special form material and shipment of radioactive material. IAEA TECDOC 1424 (2004). 7 International Atomic Energy Agency. Regulations for the safe transport of radioactive material. IAEA SSR-6 (2012). 8 National Radiation protection Agency.Guidance on professional dosimetry. NRPA Resolution 0049 (2016). © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com
TI - RADIATION PROTECTION MEASURES TAKEN DURING REPATRIATION OF SEALED HIGH ACTIVITY RADIOACTIVE SOURCES IN CAMEROON
JF - Radiation Protection Dosimetry
DO - 10.1093/rpd/ncx104
DA - 2018-02-01
UR - https://www.deepdyve.com/lp/oxford-university-press/radiation-protection-measures-taken-during-repatriation-of-sealed-high-JLcg2SBFSZ
SP - 254
EP - 259
VL - 178
IS - 3
DP - DeepDyve
ER -