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October 1, 2008

Michael T. Lesar

Chief, Rulemaking, Directives, and Editing Branch

Office of Administration

Mail Stop T-6D59

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

 

 

Re: Comments on the Security and Continued Use of Cesium-137 Chloride
Sources (Docket No. NRC-2008-0419) \[*See* 73 FR 44780 (July 31, 2008)\]

 

Dear Mr. Lesar:

 

The Radiation Research Society (RRS) greatly appreciates the opportunity
to address the U.S. Nuclear Regulatory Commission (NRC) regarding the
Security and Continued Use of Cesium-137 Chloride Sources. Given the far
reaching consequences on radiation-based research if access to cesium
chloride radiation sources is greatly limited or eliminated, the RRS
strongly urges the NRC to proceed with caution in its consideration of
these issues.

The primary reasons why cesium sources should not be eliminated at the
present time are the following:

1\) Among RRS members, more than 80% use cesium irradiators for their
research, and half of them are critically dependent upon these
irradiators.

2\) RRS members play an essential role in the development of medical
countermeasures to meet the threat of radiological/nuclear terrorism. If
cesium irradiators were eliminated, this development would suffer a
serious setback and make our country more vulnerable.

3\) RRS members are actively involved in the development of innovative
cancer treatments

involving ionizing irradiation. Cesium irradiators are essential for
much of this work, and if they are eliminated this would have a
significant impact on the advancement of radiation medicine.

These points are elaborated on in more detail below.

 

**Radiation Research Society**

The RRS is a multidisciplinary society whose main objectives are to: i)
encourage the advancement of radiation research in all areas of the
natural sciences; ii) facilitate cooperative research between the
disciplines of physics, chemistry, biology and medicine in the study of
radiation effects; and iii) promote dissemination of knowledge in these
areas through publications, meetings and education symposia. Currently
the society has over 1450 members, almost half of which are biologists
and a quarter are physicians. The rest of the membership consists of
physicists (\~ 15%), chemists (\~5%), and other disciplines. The
research and clinical interests of this group of people is multifaceted
and extensive, albeit with the common goal of advancing the
understanding of radiation effects and the advancement of radiation
medicine. The research activities of RRS members, whether basic or
translational, is dependent on peer reviewed funding from a number of
governmental (e.g. NIH, DOE, DOD, NASA, NSF, DHS) and non-governmental
(e.g. ACS, RSNA, AICR) sources. Overall, the research currently underway
by RRS members range from basic biochemical mechanisms of radiation
action, through molecular and cellular biology, *in vivo* studies of
radiation toxicity, tumor response, radiation countermeasures, to
clinical trails associated with radiation oncology. All of these
endeavors require the use of irradiation devices, and while x-ray
generators and therapeutic machines are and can be used, an overwhelming
amount of the work relies on the use of cesium irradiators. If severe
restrictions or loss of such irradiators were to occur, the impact on
radiation science would be dramatic and would severely impact the
projects heavily funded by the Federal Government.

**[Areas of Research Affected]{.underline}**

As described above, cesium chloride irradiators play an important role
in research relating to radiation effects in general, medical research
related to treating cancer, and developing countermeasures for
radiologic terrorism. Given the 1.5 million cancers diagnosed each year
in the US, and the pivotal role of radiation therapy in the management
of these diseases, it is incumbent on the research community to
vigorously address ways to optimize tumor cell kill while minimizing
adverse effects on critical normal tissues. These issues involve studies
of DNA damage/repair, molecular signaling, genetic factors affected
radiation response, stem cell biology, and normal tissue response.
Additionally, radiologic terrorism is a critical issue facing the
country and the world, and necessitates considerable research activity
to identify the risks and develop effective countermeasures. Because
this research strongly relies on the availability of cesium chloride
irradiators, the loss of such equipment would constitute a significant
obstacle to the continued progress in these critical areas.

A recent poll of RRS members indicated that 80% of the membership uses
such isotopic sources and over half of the responders indicated that
their work absolutely required these irradiators. Additionally, while
57% of responders indicated they did have some access to non-isotopic
sources (i.e. x-rays), many indicated that x-rays were not suitable for
the types of studies underway (e.g. low dose rate experiments).
Forty-three percent of those polled said they had no access whatsoever
to x-ray machines. Perhaps the most significant finding of the poll was
that 78% of those polled said that loss of isotopic sources would have
major or catastrophic consequences to their work, and by extension, the
maintenance of their laboratories. Only 15% of those polled said that
there would be no impact whatsoever if they did not have access to
cesium or other isotopic sources. The RRS is concerned that limitations
on the use of cesium chloride could adversely impact the valuable,
cutting edge research that is underway and inhibit further research that
could be instrumental in improving therapies for cancer patients and
treatments for victims of radiologic terrorism.  

**[Feasibility of Using Alternatives]{.underline}**

For some types of radiation studies it may be theoretically feasible to
replace some cesium chloride irraditors with x-ray generators. However,
there are some fundamental differences that could adversely impact
specific types of research activity. For instance it is not possible to
carry out protracted low dose rate studies with x-rays; such studies are
heavily funded by the Department of Energy's Low Dose Program. This
could have a serious impact on studies involving hematology and bone
marrow transplantation. Additionally, whole body exposures, which are
necessary to address the effects of nuclear terrorism, are more easily
performed with cesium, given it's energy spectrum and dose distribution.
The replacement of cesium irradiators with x-ray machines would require,
at the very least, rigorous on-site comparisons. This would entail
reproducing experimental studies using both machines and would
necessitate additional, and costly, technical expertise (i.e. radiation
physics support). The routine dosimetry, calibration and maintenance of
x-ray machines require far more attention from highly skilled medical
physicists, ostensibly impacting their radiotherapeutic duties. It is
the contention of the RRS that a large fraction of the research carried
out by their members cannot be adequately performed using alternative
x-ray technology.

While cobalt-60 is a viable alternative to cesium chloride, and has been
used in some radiobiological studies, considerable additional shielding
is required for cobalt units, generally necessitating specially designed
rooms, often at ground level. These requirements are costly and at many
institutions may not be feasible. Additionally the half-life of
cobalt-60 is considerably shorter than cesium, necessitating source
reloading more often (i.e. 10-15 years). This constitutes relatively
high cost and also involves critical security issues such as
transportation and disposal of the old source. In contrast, cesium
chloride irradiators are self-shielded units that are designed to
protect the integrity of and limit access to the source. Additionally,
cesium irradiators can function for 30 years before it is necessary to
reload the source or replace the entire irradiator.

**[Costs/Economic Issues]{.underline}**

The costs associated with replacing research cesium irradiators would be
extremely high. These costs include replacement as well as the
decommissioning of the cesium irradiator. Commercially available, self
shielded x-ray units do exist and are less expensive than cesium
irradiators. However, the latter can be used for 30 years with limited
maintenance, while the x-ray machines have a significantly shorter life
span (\~ 10 yr) and require more costly maintenance/quality control as
well as a highly skilled physics support staff. Perhaps most
importantly, and as cited above, a number of critical research topics
cannot be addressed using an x-ray source.

The RRS shares the concern of the American Society of Therapeutic
Radiology and Oncology (ASTRO) that the cost of acquiring an
orthovoltage x-ray unit, installing it and providing physics
support will limit development of new research facilities or cause
existing facilities to question the value of maintaining research
programs.

**[Security Issues]{.underline}**

While it is conceivable that cesium chloride could be used in the
construction of a 'dirty bomb,' it is not a trivial matter to remove
this compound from a shielded irradiator. Self-shielded irradiators
incorporate many engineering features to protect individuals from
radiation exposure and ensure that source integrity is not compromised.
The removal of a source out of the unit would require specialized
equipment and technical expertise, and theft of a self-shielded
irradiator seems extremely unlikely given the size and weight of a
typical unit.

Additionally, with the NRC's recent security-related orders in place,
there is already a high level of security around these irradiators.
Currently, cesium chloride units need to be located in secure room that
would require heavy equipment to break down the walls. Users are
required to be fingerprinted and background checks are conducted by the
FBI. There are biometric entry security systems and 24/7 security video
surveillance. If the video monitoring is impaired, guards respond
immediately to the area.

**[Transportation/Storage]{.underline}**

In agreement with ASTRO, the RRS believes that cesium chloride
irradiators present few transportation concerns. Cesium chloride's long
30-year half life ensures that the cesium sources are not transported
with any frequency. When a unit requires maintenance, the entire unit is
returned to the manufacturer. The 2-4 ton unit is packed in a
crash-resistant over-pack designed to withstand impact injuries such as
an accidental collision. Importantly, RRS and ASTRO agree that the
stockpiling of cesium from decommissioned cesium chloride irradiator
units would present a significantly more dangerous situation than
maintaining existing units in place.

Given the potential danger associated with cesium chloride, the RRS
agrees that the maintenance of cesium irradiators in a secure
environment is of critical importance. However, the RRS also contends
that it is essential to maintain the ongoing research efforts of its
members and other scientists who work with radiation. Radiation
scientists have unquestionably had a major impact on the field of
radiation oncology, helping to develop and optimize new strategies for
the treatment of cancer. Additionally, recent work is addressing the
risks of nuclear terrorism and what treatments/countermeasures will be
necessary to treat individuals exposed during an uncontrolled explosion
involving irradiation. These types of studies, and others, are heavily
funded by the Federal Government, and require the use of cesium
irradiators. The loss of such units would have a catastrophic effect on
research laboratories throughout the US, and result in loss or serious
curtailment of critical research efforts. The RRS strongly urges the NRC
to carefully consider these issues and their monetary and scientific
ramifications as they consider the security and continued use of
cesium-137 sources.

The RRS thanks you for giving us this opportunity to provide comments on
the Security and Continued Use of Cesium-137 Chloride Sources.

Sincerely,

![](media/image2.png){width="2.3375in" height="0.9527777777777777in"}

Peter Corry, Ph.D.

President RRS

![](media/image3.jpeg){width="1.7493055555555554in"
height="0.5520833333333334in"}

John R. Fike, Ph.D.

Chairman, Committee on Government

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