10/13/08 

1 Advisory Committee on the Medical Uses of Isotopes’s 

Report on 137 2 CsCl Irradiators 

3 

4 Summary 

5 

6 After studying the issues, the Advisory Committee on the Medical Uses of Isotopes 

7 (ACMUI) came to the following conclusions: 

8 1. Irradiators are necessary for medical practice and medical research. 

9 2. It is not clear from the available data that x-ray sources are biologically equivalent 

to 137 10 CsCl irradiators. 

3. Alternatives to the 137 11 CsCl irradiators currently in operation present greatly 

12 increased expense to programs that need the functionality and operational 

13 reliability of the irradiators. 

14 4. The recommendation of the National Research Council (NRC) of the National 

Academies to eliminate the use of irradiators that employ 137 15 CsCl was based on 

16 the situation at the time of their study. Since that time, security of medical 

17 irradiators units has been substantially strengthened in three ways: 

18 a. Increased security of persons with access. The December 2005 NRC 

19 orders increased the security requirements for all persons having 

unescorted access to 137 20 CsCl irradiators, including background checks, 

21 personal reference checks, and fingerprinting checks against the FBI 

22 fingerprint database. 

23 b. Increased security of the facilities housing the units, including high24 security locks on facility door, multiple doors with locks for access, 

25 motion sensors, video cameras monitored by facility security, preplanning 

26 with local law enforcement, database encryption, and secured facility 

27 schematics, and drawings. 

28 c. Increased security of the units themselves, including locks on source 

29 access panels and entry points. 

30 Given these changes, we found that the National Research Council concerns do 

31 not currently apply as previously stated, and have been superseded by increased 

32 safeguards as required by the Nuclear Regulatory Commission and state 

regulatory authorities. Well-secured 137 33 CsCl irradiators present little security 

34 hazard. 

35 

Practicality of Alternatives to 137CsCl Self-Shielded Irradiators* 36 

37 

38 Blood and Blood-Product Irradiation

39 

40 Based on our survey of the literature and other publicly available information sources, the 

41 only medical x-ray irradiator that the U.S. Food and Drug Administration (FDA) has 

42 cleared to irradiate blood and blood products to prevent graft-versus-host disease is the 

 

*

 Content taken from manuscript submitted to Health Physics June 17, 2008: Dodd, B and 

Vetter, R. “Replacement of 137Cs Irradiators with X-Ray Irradiators” 
 2

1 Raycell (Best Theratronics 2008) originally manufactured and sold by Rad Source (Rad 

2 Source 2007a) as the unit model RS 3000. Other manufacturers may also be developing 

3 plans for new irradiators. 

4 The first question regarding practicality of an x-ray machine to irradiate blood or 

5 blood products is whether there are any technical issues. Although the photon energy of 

x-ray machines is lower than those of 137 6 Cs, Janatpour et al. (2005) demonstrated that x7 ray machines can deliver the necessary 25 Gy dose with sufficient uniformity and 

8 stability to meet FDA guidelines. The typical x-ray irradiator generates a filtered energy 

9 spectrum with a peak energy of approximately 160 kVp, compared to the monoenergetic 

662 keV gamma rays from 137 10 Cs. While a radiation weighting factor of 1 is applied to 

11 both gamma rays and x rays for radiation protection purposes (NCRP 1993), the 

12 biological effectiveness of low energy photons is approximately twice that of 662 keV 

137 13 Cs gamma rays (ICRU 1986). Consequently, a dose of 25 Gy delivered by an x-ray 

irradiator will not produce the same biological effect as 25 Gy from 137 14 Cs gamma rays. 

15 The significance of this difference in radiation effectiveness relevant to transfusion 

16 medicine and immunological research is unknown. 

17 Regarding costs, the NRC study (2008) quoted about $180,000 for a new x-ray 

18 irradiator and an annual service agreement cost of just over $10,000. However, the actual 

19 cost of the x-ray system has increased. In May 2008 this manufacturer quoted a purchase 

20 price of $250,0000 and $66,000 for a 3-year maintenance contract including a routine 

21 service call and one set of replacement parts as needed. While the purchase price might 

be about the same as a 137 22 Cs irradiator, the annual maintenance cost with a service 

23 agreement may be much greater unless the owner has engineering capabilities to provide 

24 service and maintenance in-house. Also, the service contract does not include physics 

25 services. Depending on the number of set-ups, calibration costs may exceed $10,000 per 

26 year if outside physics services are required. In addition, there would be a one-time cost 

27 of installing a 240 volt line to the room for most of the x-ray units replacing a cesium 

28 irradiator. 

29 Based on repair history of clinical x-ray machines, a user of an x-ray irradiator 

30 may experience a higher failure rate and require more service and down-time than a 

137 31 CsCl irradiator. Since maintenance of an irradiated blood supply is important, 

32 purchasers of x-ray blood irradiators find it necessary to purchase an annual maintenance 

33 agreement. However, outside service can result in a facility being unable to perform life34 saving irradiations for a time. For example, one owner experienced a service response 

35 and re-calibration time of two weeks. Both the upper and lower power supplies had to be 

36 replaced after a few years of operation. Therefore, blood banks and hospitals may need 

37 to plan for an alternative means of irradiation or an alternative supply of irradiated blood 

components to meet critical demand. Without 137 38 CsCl as an alternative, the facility may 

39 have to purchase two units to assure a continuous supply of irradiated blood. 

40 Another factor to evaluate for practicality is the throughput of an x-ray irradiator. 

41 Two units of blood can be irradiated at one time with the Raycell, and irradiation time is 

42 about 5 min. This is sufficient for two blood centers contacted, which do about 30-100 

43 units per month, and it is adequate for a clinic doing about 20 units per day. However, a 

44 significant workload like that at a large academic medical center with a throughput of 50-

45 60 units per day may exceed the capabilities of a single x-ray unit. While it may seem 

46 that the exposure rate with the x-ray would keep up with the demand, the blood 
 3

1 irradiation is not continually as with an assembly line. Rather, units are irradiated as 

2 needed based on the clinical demand, in irregular intervals. Thus, the duration required 

3 for the irradiation becomes an important limiting factor. One potential buyer stated that 

4 about 48,000 blood products could be irradiated within the x-ray tubes’ 2000-h warranty 

5 period (Blood Bank Talk 2007). For a site processing 50 units per day and assuming that 

6 procedures requiring irradiated blood happen mostly during normal work days, that 

7 would imply the need for a new tube each 3.7 years, adding considerably to the cost of 

8 the operation. 

Since 137 9 Cs has a half-life of 30 years, it is not financially practical to replace 

10 those units that were installed within the last 15 years. Ease of use is comparable 

between the 137 11 CsCl irradiator and the x-ray irradiator. 

12 One issue that has not been investigated is whether all the operating cesium 

13 irradiators could afford to replace the units, or whether some facilities will cease 

14 operation, depriving patients of irradiated blood and researchers a source of radiation. 

15 

16 Biomedical and Small Animal Irradiators 

17 

18 Ten x-ray irradiators are commercially available for cell, tissues and small animals, eight 

19 from three U.S. manufacturers and two irradiators from outside the U.S. A few will be 

20 discussed as being representative of the issues. 

21 The RS 2000 (Rad Source 2007b) has been sold by Rad Source since 1999, with 

22 about 15-20 units placed in Europe and Asia and 50-60 placed in the USA. Several users 

23 contacted seem satisfied with the device. The purchase price is little over $100,000, and 

24 a service agreement is around $10,000 per year. Apparently reliability has been good; 

25 however, owners should expect to refurbish or replace the power supply about every 4-5 

26 years. 

27 The Rad Source RS 2400 (Rad Source 2007c), operating between 80 and 160 kV, 

28 delivers a higher dose rate using a new technology emitter. This 4-pi x-ray source may 

have the capability of eventually delivering about 300 Gy min-1 29 , but the two RS 2400s 

30 operated considerably lower than this. The International Atomic Energy Agency is 

31 testing one of these units for its sterile insect programs. The dose rate and irradiation 

32 volume of the RS 2400 are much larger than those for the RS 2000 and may allow five 

450-ml blood bags to be irradiated simultaneously at a dose rate about 45 Gy min-1 33 . 

34 However, the canister loading methodology may need some redesign before it would be 

35 practical for irradiation of blood. Rad Source expects to submit its application for FDA 

36 approval for irradiation of blood products with this device in 2008. The RS 2400 is 

37 expected to sell for about $200,000 - 250,000 with an annual service contract of about 

38 $20,000. To ensure a high degree of reliability and minimal down time, the service 

39 agreement will include a tube replacement every 2000 h. 

40 Faxitron (2008) sells two irradiation systems, the RX-650 and the CP-160, with 

41 prices around $43,000 and $87,000 respectively. The Faxitron RX-650 operates at a peak 

42 energy of only 130 kVp. To achieve adequate uniformity of dose, Kennedy et al. (2004) 

43 had to irradiate the mice from several directions because of the attenuation of the lower 

44 energy radiation in the bodies of the mice. Woo and Nordal (2006) concluded that the 

45 Faxitron CP-160 could be useful for small animal research if radiation was delivered 

46 carefully to ensure accurate and uniform radiation dose. The authors stated that at a 
 4

1 distance of 33 cm the indicated beam diameter on the tray was 26 cm, whereas the part of 

2 the beam where the uniformity as within 10% was confined to a diameter of 16 cm. 

3 Precision X-Ray Inc. (2005) sells four different biomedical and small animal x4 ray irradiators with energies ranging from 160 kVp to 320 kVp. With 0.5 mm Cu and 

5 operating at 320 kV, the unit delivers a dose rate of 2 Gy/minute. The higher tube 

potential brings the RBE to the same value as the 137 6 Cs gamma ray beam. The price runs 

7 around $170,000, exclusive of the service contract. 

8 Kimtron markets units similar to the Precision X-ray units, with four units 

9 operating between 160 kV and 450 kV. The prices appear comparable to similar units. 

10 Gilardoni, an Italian company, sells the Radgil (Gilardoni 2000) with an energy 

of 200 kVp and a dose rate of about 1 Gy min-1 11 at a cost of about 94,000 Euros 

12 (~$146,000). 

13 Hitachi (2008) manufactures the MBR-1520-3, which is a 150-kVp blood 

14 irradiator that can deliver doses from 15 to 35 Gy in 5-Gy increments. However, there is 

15 no indication of FDA approval for human use. 

16 

17 AAPM Survey of Users 

18 

19 The American Association of Physicists in Medicine (AAPM) conducted a survey of its 

20 members in August to assess their experience with irradiators. The results of the survey 

21 would be skewed toward hospital-based or university-based irradiators; however, for the 

22 information gathered, that should not affect the conclusions. The survey, since it was 

23 targeted at medical physicists and some health physicists, represents only a small part of 

24 the irradiators in use. Of the 363 respondents, 297 had irradiators, 84.6% of those used 

137 25 Cs as the source, 9.3% used conventional x-ray units and 6% used medical linear 

accelerators (linacs). The 137 26 CsCl units represented the major vendors. Only 10% were 

27 purchased within the last two years, with 7% planning on replacing the units within the 

28 next 5 years. 

A quarter of the 137 29 CsCl units had had some malfunction but most were repaired 

30 in less than 7 days. Of the x-ray units, 35% had malfunctions, with 44% being repaired 

31 within 7 days. 

32 Only 40% of the cesium units were used for blood irradiation, with about 25% 

33 used for material irradiations and another 25% for animal irradiations. Of the x-ray units, 

34 half were for blood irradiation, while 19% were for material irradiation and 32% for 

35 animals. Forty percent of the medical linacs for the respondents were used 

36 predominantly for blood irradiation and 11% for animals. 

37 This survey indicates that, while fairly reliable, conventional x-ray units and 

38 medical linacs account for a small minority of the irradiators in the field. They had 

slightly more downtime than 137 39 CsCl units. The cesium units have also been reliable and 

40 their users, in general, have no plans to replace them. Forced removal of the cesium 

41 irradiators would result in a very large loss of resources, both radiation sources and funds, 

42 not only for blood banks but research institutions as well. 

43 
 5

1 Linear Accelerators 

2 

3 Medical linear accelerators (linacs) can and do provide irradiation for blood 

4 products and materials. While linacs can serve for animal irradiation, their use with mice 

5 presents some difficulties because of the build-up region in the dose that is on the order 

6 of the thickness of a mouse. Most facilities that use linacs for irradiation either are part 

7 of larger processing facilities (for example, medical product sterilization companies) or 

8 find time between patients (creating problems in scheduling and staffing) in a 

9 radiotherapy clinic because of the extremely large initial investment, about $2,000,000 

10 for these units and the cost for maintenance of $200,000 per year. Night time irradiations 

11 pose additional staffing issues. Because of the costs, linacs are not a viable replacement 

for 137 12 CsCl irradiators for the vast majority of facilities. 

13 

14 Alternative Radionuclides 

15 

16 At the time of writing, the only reasonable alternative radionuclide source for 

irradiators would be 60 17 Co. This radionuclide is used in large industrial irradiators, but is 

not currently available for blood or research irradiators. The use of 60 18 Co would require 

frequent source change due to the much shorter half-life compared with 137 19 Cs (5.27 years 

20 compared with 30 years), and higher initial source activities to extend the useful life of 

the sources. The 60 21 Co also requires thicker shielding because of the higher energy (1.2 

22 cm half-value layer in lead compared with 0.6 cm.) Since the half-value layer enters into 

23 shielding as an exponent, the difference in the thickness of shield required due to the 

24 differences in the values multiples rapidly. These two considerations would lead to high 

25 initial costs for a unit and frequent, repetitive costs for source replacement. Finally, there 

is no convincing evidence that the 60 26 Co sources of any form would pose less of a hazard 

than the 137 27 CsCl. 

28 

29 Further Considerations for Blood Irradiation 

30 

31 The subcommittee consulted 10 hematologists or oncologists and one clinical laboratory 

32 director. These included researchers at one of the nation’s most prestigious blood 

disorder and hematologic cancer research centers having extensive use of 137 33 CsCl blood 

34 and small animal irradiators. 

35 Most of the previous information, such as in the National Research Council 

36 report, focused use of irradiators at central blood banks. 

37 Five of the 10 hematologists/oncologists reported that they regularly prescribe 

38 irradiated blood for transfusions. Of these, one said that up to 40% of all blood he 

39 prescribed was irradiated. The others estimated that 15% to 33% of all blood for 

40 transfusion was irradiated. They all mentioned that their patient population was the 

41 reason why they tended to prescribe more irradiated blood products than the nominal 

42 10% that often is used for planning. Patients who are post transplant are one such 

43 category, although none of these physicians had many patients in this subset. The more 

44 common reason was the use of certain chemotherapeutics that severely affect the host 

45 immune system. 
 6

Although no surveyed physicians were aware of difference between 137 1 Cs 

2 irradiated blood vs. x-ray, all ten (including one physician who doesn't presently 

3 routinely give irradiated blood transfusions) stated a regulation to eliminate or reduce the 

availability of irradiated blood products, or access to 137 4 CsCl irradiators would represent 

5 a severe drawback in the hematology/oncology field of medical practice and research. 

6 One physician who prescribes irradiated blood 40% of the time said that hematologists 

7 and oncologist prescribe irradiated blood about 33% of the time and that figures which 

8 say that only around 10% of all transfused blood is irradiated are skewed by the trauma9 related transfusions in hospital emergency rooms and for surgery-related transfusions. 

10 Oncologists might rely more on irradiated blood than other medical professionals. 

11 One institution specializing in research on hematologic malignancies reported that 

four 137 12 CsCl irradiators are used by 250 authorized users at a frequency of about 30 to 40 

13 times per day in support of about 20 research projects and eight active clinical trials. 

Although comparable x-ray systems could be obtained to replace the 137 14 CsCl irradiators, 

15 four physician/PhD researchers indicated that the change would require more than a year 

16 to develop the radiation response relationships between the radionuclide-source and x-ray 

17 source irradiators, and that impacts on ongoing funded research would be enormous. 

18 None of the physicians or the lab director had knowledge of the radiobiological 

differences between samples irradiated by x-rays or monoenergetic photons from 137 19 Cs 

20 sources. Four of six hematologists had experience with both irradiator systems. Three 

21 also had experience also with linac irradiated blood before their institutions obtained 

22 dedicated blood irradiators. 

23 

137 24 Cesium Chloride Irradiator Security 

25 

26 Prior to the publication of the National Research Council report the U.S. Nuclear 

27 Regulatory Commission (NRC) has disseminated orders to licensees for increased 

28 controls on sources of radioactive material in quantities of concern. The "Orders 

29 Imposing Increased Controls" issued in December 2005 contain requirements based on 

30 the International Atomic Energy Agency Code of Conduct. These measures were 

31 required to safeguard radioactive sources from theft or other unauthorized use. These 

32 requirements include: 

33 1. Limit access to approved individuals who need to use radioactive materials in 

34 performing work activities. 

35 2. Perform background and trustworthiness checks on all employees with access. 

36 3. Escort all service providers who need to access the radioactive source. 

37 4. Document the monitoring of sources with means for detecting source removal. 

38 5. Increase source monitoring during source delivery or shipment. 

39 6. Respond immediately to any attempted theft, sabotage, or diversion of sources. 

40 7. Develop a plan for assistance from supporting authorities in the event of theft, 

41 sabotage, or diversion. 

42 8. Provide means for transmitting information between personnel and components used 

43 to detect an intrusion. 

44 9. Notify the NRC Operations Center of any attempted theft of radioactive material. 

45 10. Document any attempt at theft or diversion of radioactive material. 
 7

1 11. Use trusted carriers with package tracking systems, who maintain constant control 

2 during transit, and who maintain communication for response or assistance. 

3 12. Notify the NRC 90 days prior to certain shipments. 

4 To review the changes resulting from the NRC orders for increased controls, a site 

5 visit for one of the members of this subcommittee was arranged to a major medical center 

with four 137 6 CsCl blood irradiators. The visit found that the licensee maintained access 

7 control to the irradiators by the means required in the Order, including: 

8 1. Allowing access only to approved personnel who had undergone a thorough FBI 

9 background check, fingerprinting, work history review, psychological review, and 

10 local law enforcement background check. 

11 2. Allowing access only to persons needing and trained to use the irradiators properly. 

12 3. Providing redundant enforced doors, locks, heavy walls, computer-coded key-card 

13 access, and continuous video monitoring of the halls, entry, and workspace occupied 

14 by the irradiator units. 

15 4. Presenting documented procedures to ensure that authorized users support the 

16 institutions system to prevent unauthorized access and protect access information, 

17 drawings, schematics, maps, and facility floor plans from unauthorized use. 

18 5. Coordinating with local law enforcement agencies for rapid response to any 

19 attempted intrusion or theft of radioactive material. 

20 In addition, we found the irradiator systems to be outfitted with additional 

21 padlocks and security measures for preventing unauthorized access to radioactive sources 

22 inside the irradiators. The irradiators weigh 4000 to 5000 pounds and do not have 

23 wheels. 

In summary, we found highly increased security of 137 24 CsCl irradiators and 

25 increased controls over access by authorized personnel at the institution. It would be 

26 very difficult, even for personnel with access permission, to attempt theft, diversion, or 

misuse of the 137 27 CsCl irradiator systems. The institution had implemented all 

requirements to enhance the security of 137 28 CsCl irradiator systems in a manner typical of 

29 such irradiators. 

30 In addition to the increased security enhancements required by the NRC, an 

31 initiative by the Department of Energy (DOE), the Department of Homeland Security 

(DHS), and the Domestic Nuclear Detection Office will harden 137 32 CsCl irradiators 

throughout the United States to delay unauthorized access to 137 33 Cs sources. This has 

34 been a cooperative effort for the past 18 months. The demonstration project was 

35 completed in March of 2008 and the pilot project is currently being conducted in nine 

36 facilities. DOE and DHS anticipate that this pilot program will be completed later this 

37 year. 

38 The pilot project is the actual enhancement of the irradiators in the field. The 

39 manufacturer will install additional material and make minor changes to the exterior of 

40 the irradiator to make it more difficult to remove the source(s). There are nine facilities 

41 that have volunteered to participate. The pilot will have two of the manufacturers visit 

42 the facility and add the enhancements to the irradiators. The pilot will demonstrate the 

43 ease and ability of performing these tasks in a “real world” environment. The pilot will 

44 also validate the costs to perform the retrofit. It is estimated that the cost will be $2,000 

45 to 4,000 for each device. The DHS and the DOE will pay the manufacturers for the 
 8

1 enhancements. It is expected that the pilot will be successful and the project will be open 

2 to all of the devices currently licensed in the United States. 

3 

Alternative Forms for 137 4 Cesium Sources 

5 

6 The subcommittee considered whether this report should recommend to 

manufacturers of 137 7 CsCl irradiators that alternatives to the powder form of the source be 

8 pursued. However, as of this time, there is no convincing evidence that another form, 

9 particularly a solid form, would be safer. While a powder may be dispersed by a bomb, a 

10 solid poses a radiation hazard much greater than the dispersed powder. In addition, the 

11 manufacture of a solid source could pose a hazard to the workers making the sources. 

12 

13 Conclusions 

14 

15 1. Cesium-137 irradiators are used in a number of important medical and research 

16 applications. As the population of the United States ages, the use of irradiated 

17 blood products will escalate, producing an increased demand for the availability 

18 of this technology for patient safety. The need for medical irradiators is 

19 unquestionable. 

20 2. Some investigators are concerned about the ways that differences in radiation 

quality between 137 21 CsCl irradiators and x-ray systems would affect experimental 

22 results on blood samples, small animals, separated T-cells and stem cells, and 

23 other biological media. 

3. Alternatives to 137 24 CsCl irradiators are expensive, and forcing the switch to x-ray 

25 sources would place an unnecessary and great financial burden on blood banks 

26 and research institutions. 

4. The ACMUI subcommittee believes that the 137 27 Cesium Chloride Irradiator 

28 Security Enhancements and Increased Controls and Security Inspections have 

provided strong measures for ensuring the safety and integrity of 137 29 CsCl sources 

30 in medical irradiators, have reduced the vulnerability of these devices as material 

31 suitable for malicious intent, and should prove to be acceptable as an alternative 

32 to removal or prohibition of these devices. 

33 

ACMUI 137 34 CsCl Irradiator Subcommittee 

35 

Debbie Gilley1,2 36 

Darrell Fisher3,4 37 (Lead of the Security Subgroup) 

Ralph Lieto2 38 

Orhan Suleiman2,3 39 

Bruce Thomadsen2 40 (Chair) 

Richard Vetter1 41 (Lead of the X-ray Alternative Subgroup) 

James Welsh3 42 (Lead of the Need Subgroup) 

1 43 Member, X-ray Alternative Subgroup 

2 44 Member, Security Subgroup 

3 45 Member, Need Subgroup 

46 
 9

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