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Process control and dosimetry in a multipurpose irradiation facility
Radiation Physics and Chemistry 55 (1999) 781±784
www.elsevier.com/locate/radphyschem
Process control and dosimetry in a multipurpose irradiation facility E.G. Cabal®n*, L.G. Lanuza, H.M. Solomon Philippine Nuclear Research Institute, Diliman, Quezon City, Philippines
Abstract Availability of the multipurpose irradiation facility at the Philippine Nuclear Research Institute has encouraged several local industries to use gamma radiation for sterilization or decontamination of various products. Prior to routine processing, dose distribution studies are undertaken for each product and product geometry. During routine irradiation, dosimeters are placed at the minimum and maximum dose positions of a process load. # 1999 Published by Elsevier Science Ltd. All rights reserved.
1. Introduction
2. Description of the irradiation facility
Radiation processing has found industrial applications in radiation sterilization of medical and pharmaceutical products, decontamination of pharmaceutical and cosmetic raw materials and for food preservation. To introduce and demonstrate this new technology to the local industries, the Philippine Nuclear Research Institute (PNRI) with the technical assistance of the International Atomic Energy Agency (IAEA) has set up a multipurpose gamma irradiation facility. The eorts of PNRI have paid o. Several local industries are aware of and though still in a limited scale are now using radiation for the sterilization or decontamination of their products, such as empty aluminum tubes, empty gelatin capsules, orthopedic implants, spices and dried vegetables. Because it is a multipurpose gamma irradiation facility, dierent types of products with dierent geometry and density are treated in the facility.
The Gammabeam 651PT, a batch type irradiator from Nordion International is designed for research and pilot scale studies. The source con®guration consists of eight source racks, each of which can be operated independently and can be raised to seven dierent irradiation positions. Eectively, the source con®guration can be considered as a plane or plaque source, 112 cm wide by 140 cm high. In August, 1998 total 60 Co activity was about 4.5 PBq (120,000 Ci). Products for irradiation originally were loaded on four turntables, which were located on both sides of the source plaque. The turntables made four quarter turns per batch. To improve the throughput of the facility, a new product handling system was locally fabricated (Cabal®n et al., 1996). Instead of the turntables, two rows of rails were installed on each side of the source plaque. Product boxes are stacked on ``carriers'', which are then placed on the rails. At most three carriers can be located on each rail. To simulate a four pass shue-dwell type conveyor, each carrier remains in each position for a preset dwell time and then transferred manually from one position to the next. The mid-height of a process unit (loaded on a
* Corresponding author. Fax: (63 2) 920-16-46.
0969-806X/99/$ - see front matter # 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 9 ) 0 0 3 0 3 - 5
782
E.G. Cabal®n et al. / Radiation Physics and Chemistry 55 (1999) 781±784
Fig. 1. Demonstration of consistency of dose received by the products. Product: spices, density=609 kg/m3; Dosimeter: ECB; Irradiation time: 6.44 h (dwell time: 12 32.2 min); Product location: Rails; Box size: 49.5 25 37.5 cm).
turntable or carrier) is located to coincide with the mid-height of the source plaque, resulting in a source overlap con®guration. 3. Dosimeters Because it is a multipurpose irradiation facility, dierent types of products requiring a wide range of
doses are treated in this facility. The dosimeters used therefore cover the dose range from 40 Gy to 50 kGy. Fricke dosimeter (ASTM, 1994b) is used for food irradiation dose control in the dose range of 40±400 Gy, as well as to calibrate other dosimeters and to carry out dose distribution studies. Ethanol monocholorobenzene (ECB) dosimeter (ASTM, 1994a) is used for routine dose control in radiation sterilization and decontamination in the dose range of 1±50 kGy. The
E.G. Cabal®n et al. / Radiation Physics and Chemistry 55 (1999) 781±784
absorbed dose is evaluated using oscillometric method by the Radelkis OK-302/1 oscillotitrator from Hungary. The dose response of the ECB dosimeter was determined by irradiating the dosimeter solution to ``known'' doses in a Gammacell-220, where dose rate has been previously determined by Fricke dosimeter. PNRI has participated in the International Dose Assurance Service (IDAS) of IAEA. Alanine dosimeters from IDAS were irradiated together with Fricke or ECB dosimeters at the center of a dummy product box. Results over a span of nine years have shown that absorbed dose as measured by alanine agreed with ECB within 5%, while Fricke dosimeter agreed within 2%. 4. Process control Good radiation practice (Codex, 1984; IAEA, 1977; ISO, 1995; McLaughlin et al., 1989) requires that whenever there are changes in source loading, product±source distance, product density, product con®guration or anything which can aect the dose received by the product, dose distribution in the product should be determined. During product validation dose distribution within the product package is determined leading to the localization of minimum and maximum dose positions. The minimum dose is required to achieve the desired eect, while the maximum dose must be controlled to avoid adverse eects on the products. The appropriate loading pattern is determined for each product and for each type of product con®guration, such as product size, product bulk density and source±product geometry. The locations of minimum and maximum absorbed dose for a speci®c product and product loading pattern are determined prior to routine irradiation. This is accomplished by placing several dosimeters in the product. If the dose distribution studies for a particular loading pattern show that dose uniformity ratio (ratio of maximum dose to minimum dose) is not within the limits acceptable for the product, a new product loading pattern is chosen and dose distribution studies repeated. Based on the results of dose distribution studies, a relationship between the dose absorbed by the product and operating parameters of the facility (cycle time or time of irradiation) is established. The dose distribution measurements were carried out with three dierent products, i.e., empty aluminum capsules (r=105 kg mÿ3), empty gelatin capsules (r=76 kg mÿ3) and spices (r=609 kg mÿ3). The size of the product boxes are 60 40 52 cm for capsules and 50 25 38 cm for spices. The distribution studies with dierent product geometry and densities show
783
Table 1 Dose mapping of a process unit on a turntablea Plane no.
Columns
1
I. Front plane
Top row
2.16 1.96 2.06 2.44 2.27 2.33 2.67b 2.44 2.59 2.57 2.41 2.54 2.25 2.02 2.22 1.97 1.83 1.80 1.82 1.94 2.31 2.04 2.22 2.54 2.22 2.50 2.46 2.13 2.38 1.98 1.79 1.71c 1.77 1.93 2.02 1.91 2.09 2.32 2.17 2.37 2.56 2.38 2.59 2.51 2.32 2.49 2.21 1.98 2.18
a b Middle row c d Bottom row e II. Middle plane a b c d e III. Black plane a b c d e
3
5
7
9
a Results in kGy/h; Dosimeter: Fricke; Irradiation time: 6.8 min (during dose mapping); Product: empty aluminum tubes, density=105 kg/m3; Box size: 59.5 40 52 cm. b Maximum dose position: Ic1. c Minimum dose position: Ile5.
that the minimum dose is always in the mid-plane of the product boxes in each type of products. In the case of irradiation carried out on rails the Dmin is always in the side of the mid-plane of the process unit. In those cases when the irradiation was performed on turntables the minimum dose was measured in the top or bottom position of the center line of the mid-plane. The maximum dose, on the other hand, is always found on the outer planes. The dose uniformity ratio was 1.7 or 1.8 for the empty tubes and gelatin capsules, while in the case of the dense spices it was 1.8 and 2.2 for rails and turntables, respectively. The exact location however is dependent on the product density, product con®guration and source to product geometry. During routine irradiation dosimeters are placed at the minimum and maximum absorbed dose positions. The results of irradiation of several batches of spices, done over a span of six months are shown in Fig. 1. Conditions for irradiation were similar except for the irradiation time, which was adjusted to correct for 60 Co decay. Consistency of the dose received by the product is demonstrated.
Acknowledgements We thank our colleagues, A. Maningas, G. Madera, F. Pancho, F. Pares and R. Gallardo of the Irradiation Services, PNRI for their assistance and support in carrying out our work.
784
E.G. Cabal®n et al. / Radiation Physics and Chemistry 55 (1999) 781±784
References ASTM, 1994a. Standard practice for use of the ethanol-chlorobenzene dosimetry system. In: E-1538-93, Annual Book of ASTM Standards, vol. 12.02. American Society for Testing and Materials, Philadelphia, PA, USA, p. 826. ASTM, 1994b. Standard practice for using the Fricke reference standard dosimetry system. In: E-1026-92, Annual Book of ASTM Standards, vol. 12.02. , American Society for Testing and Materials, Philadelphia, PA, USA, p. 593. Cabal®n, E.G. et al., 1996 Innovations to increase throughput of multipurpose irradiation facility, Phil. Nucl. J (in press).
Codex, 1984 General Standard for Irradiated Foods and Recommended International Code of Practice for Operation of Radiation Facilities used in the Treatment of Foods, CAC/VOL. XV, Ed.1, FAO/WHO, Rome. IAEA, 1977. Manual of Food Irradiation Dosimetry, Technical Report Series No. 178. International Atomic Energy Agency, Vienna. ISO, 1995. Sterilization of health care productsÐrequirements for validation and routine controlÐradiation sterilization, ISO 11137. McLaughlin, W.L., Boyd, A.W., Chadwick, K.H., McDonald, J.C., Miller, A., 1989. Dosimetry for Radiation Processing. Taylor and Francis, London.
www.elsevier.com/locate/radphyschem
Process control and dosimetry in a multipurpose irradiation facility E.G. Cabal®n*, L.G. Lanuza, H.M. Solomon Philippine Nuclear Research Institute, Diliman, Quezon City, Philippines
Abstract Availability of the multipurpose irradiation facility at the Philippine Nuclear Research Institute has encouraged several local industries to use gamma radiation for sterilization or decontamination of various products. Prior to routine processing, dose distribution studies are undertaken for each product and product geometry. During routine irradiation, dosimeters are placed at the minimum and maximum dose positions of a process load. # 1999 Published by Elsevier Science Ltd. All rights reserved.
1. Introduction
2. Description of the irradiation facility
Radiation processing has found industrial applications in radiation sterilization of medical and pharmaceutical products, decontamination of pharmaceutical and cosmetic raw materials and for food preservation. To introduce and demonstrate this new technology to the local industries, the Philippine Nuclear Research Institute (PNRI) with the technical assistance of the International Atomic Energy Agency (IAEA) has set up a multipurpose gamma irradiation facility. The eorts of PNRI have paid o. Several local industries are aware of and though still in a limited scale are now using radiation for the sterilization or decontamination of their products, such as empty aluminum tubes, empty gelatin capsules, orthopedic implants, spices and dried vegetables. Because it is a multipurpose gamma irradiation facility, dierent types of products with dierent geometry and density are treated in the facility.
The Gammabeam 651PT, a batch type irradiator from Nordion International is designed for research and pilot scale studies. The source con®guration consists of eight source racks, each of which can be operated independently and can be raised to seven dierent irradiation positions. Eectively, the source con®guration can be considered as a plane or plaque source, 112 cm wide by 140 cm high. In August, 1998 total 60 Co activity was about 4.5 PBq (120,000 Ci). Products for irradiation originally were loaded on four turntables, which were located on both sides of the source plaque. The turntables made four quarter turns per batch. To improve the throughput of the facility, a new product handling system was locally fabricated (Cabal®n et al., 1996). Instead of the turntables, two rows of rails were installed on each side of the source plaque. Product boxes are stacked on ``carriers'', which are then placed on the rails. At most three carriers can be located on each rail. To simulate a four pass shue-dwell type conveyor, each carrier remains in each position for a preset dwell time and then transferred manually from one position to the next. The mid-height of a process unit (loaded on a
* Corresponding author. Fax: (63 2) 920-16-46.
0969-806X/99/$ - see front matter # 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 9 ) 0 0 3 0 3 - 5
782
E.G. Cabal®n et al. / Radiation Physics and Chemistry 55 (1999) 781±784
Fig. 1. Demonstration of consistency of dose received by the products. Product: spices, density=609 kg/m3; Dosimeter: ECB; Irradiation time: 6.44 h (dwell time: 12 32.2 min); Product location: Rails; Box size: 49.5 25 37.5 cm).
turntable or carrier) is located to coincide with the mid-height of the source plaque, resulting in a source overlap con®guration. 3. Dosimeters Because it is a multipurpose irradiation facility, dierent types of products requiring a wide range of
doses are treated in this facility. The dosimeters used therefore cover the dose range from 40 Gy to 50 kGy. Fricke dosimeter (ASTM, 1994b) is used for food irradiation dose control in the dose range of 40±400 Gy, as well as to calibrate other dosimeters and to carry out dose distribution studies. Ethanol monocholorobenzene (ECB) dosimeter (ASTM, 1994a) is used for routine dose control in radiation sterilization and decontamination in the dose range of 1±50 kGy. The
E.G. Cabal®n et al. / Radiation Physics and Chemistry 55 (1999) 781±784
absorbed dose is evaluated using oscillometric method by the Radelkis OK-302/1 oscillotitrator from Hungary. The dose response of the ECB dosimeter was determined by irradiating the dosimeter solution to ``known'' doses in a Gammacell-220, where dose rate has been previously determined by Fricke dosimeter. PNRI has participated in the International Dose Assurance Service (IDAS) of IAEA. Alanine dosimeters from IDAS were irradiated together with Fricke or ECB dosimeters at the center of a dummy product box. Results over a span of nine years have shown that absorbed dose as measured by alanine agreed with ECB within 5%, while Fricke dosimeter agreed within 2%. 4. Process control Good radiation practice (Codex, 1984; IAEA, 1977; ISO, 1995; McLaughlin et al., 1989) requires that whenever there are changes in source loading, product±source distance, product density, product con®guration or anything which can aect the dose received by the product, dose distribution in the product should be determined. During product validation dose distribution within the product package is determined leading to the localization of minimum and maximum dose positions. The minimum dose is required to achieve the desired eect, while the maximum dose must be controlled to avoid adverse eects on the products. The appropriate loading pattern is determined for each product and for each type of product con®guration, such as product size, product bulk density and source±product geometry. The locations of minimum and maximum absorbed dose for a speci®c product and product loading pattern are determined prior to routine irradiation. This is accomplished by placing several dosimeters in the product. If the dose distribution studies for a particular loading pattern show that dose uniformity ratio (ratio of maximum dose to minimum dose) is not within the limits acceptable for the product, a new product loading pattern is chosen and dose distribution studies repeated. Based on the results of dose distribution studies, a relationship between the dose absorbed by the product and operating parameters of the facility (cycle time or time of irradiation) is established. The dose distribution measurements were carried out with three dierent products, i.e., empty aluminum capsules (r=105 kg mÿ3), empty gelatin capsules (r=76 kg mÿ3) and spices (r=609 kg mÿ3). The size of the product boxes are 60 40 52 cm for capsules and 50 25 38 cm for spices. The distribution studies with dierent product geometry and densities show
783
Table 1 Dose mapping of a process unit on a turntablea Plane no.
Columns
1
I. Front plane
Top row
2.16 1.96 2.06 2.44 2.27 2.33 2.67b 2.44 2.59 2.57 2.41 2.54 2.25 2.02 2.22 1.97 1.83 1.80 1.82 1.94 2.31 2.04 2.22 2.54 2.22 2.50 2.46 2.13 2.38 1.98 1.79 1.71c 1.77 1.93 2.02 1.91 2.09 2.32 2.17 2.37 2.56 2.38 2.59 2.51 2.32 2.49 2.21 1.98 2.18
a b Middle row c d Bottom row e II. Middle plane a b c d e III. Black plane a b c d e
3
5
7
9
a Results in kGy/h; Dosimeter: Fricke; Irradiation time: 6.8 min (during dose mapping); Product: empty aluminum tubes, density=105 kg/m3; Box size: 59.5 40 52 cm. b Maximum dose position: Ic1. c Minimum dose position: Ile5.
that the minimum dose is always in the mid-plane of the product boxes in each type of products. In the case of irradiation carried out on rails the Dmin is always in the side of the mid-plane of the process unit. In those cases when the irradiation was performed on turntables the minimum dose was measured in the top or bottom position of the center line of the mid-plane. The maximum dose, on the other hand, is always found on the outer planes. The dose uniformity ratio was 1.7 or 1.8 for the empty tubes and gelatin capsules, while in the case of the dense spices it was 1.8 and 2.2 for rails and turntables, respectively. The exact location however is dependent on the product density, product con®guration and source to product geometry. During routine irradiation dosimeters are placed at the minimum and maximum absorbed dose positions. The results of irradiation of several batches of spices, done over a span of six months are shown in Fig. 1. Conditions for irradiation were similar except for the irradiation time, which was adjusted to correct for 60 Co decay. Consistency of the dose received by the product is demonstrated.
Acknowledgements We thank our colleagues, A. Maningas, G. Madera, F. Pancho, F. Pares and R. Gallardo of the Irradiation Services, PNRI for their assistance and support in carrying out our work.
784
E.G. Cabal®n et al. / Radiation Physics and Chemistry 55 (1999) 781±784
References ASTM, 1994a. Standard practice for use of the ethanol-chlorobenzene dosimetry system. In: E-1538-93, Annual Book of ASTM Standards, vol. 12.02. American Society for Testing and Materials, Philadelphia, PA, USA, p. 826. ASTM, 1994b. Standard practice for using the Fricke reference standard dosimetry system. In: E-1026-92, Annual Book of ASTM Standards, vol. 12.02. , American Society for Testing and Materials, Philadelphia, PA, USA, p. 593. Cabal®n, E.G. et al., 1996 Innovations to increase throughput of multipurpose irradiation facility, Phil. Nucl. J (in press).
Codex, 1984 General Standard for Irradiated Foods and Recommended International Code of Practice for Operation of Radiation Facilities used in the Treatment of Foods, CAC/VOL. XV, Ed.1, FAO/WHO, Rome. IAEA, 1977. Manual of Food Irradiation Dosimetry, Technical Report Series No. 178. International Atomic Energy Agency, Vienna. ISO, 1995. Sterilization of health care productsÐrequirements for validation and routine controlÐradiation sterilization, ISO 11137. McLaughlin, W.L., Boyd, A.W., Chadwick, K.H., McDonald, J.C., Miller, A., 1989. Dosimetry for Radiation Processing. Taylor and Francis, London.