Low Energy & Portable Hand Held X-Rays
State regulations require that all x-ray machines that are to be operated on the Oklahoma
State University campus and used for research purposes be registered with the state
and included on the campus inventory of radiation producing machines. This requirement
covers both “true” x-ray machines (e.g. XRDs, XRFs, DEXA units, Micro CTs) and what
some are sometimes referred to as “low energy” x-ray machines (e.g. XRDs and XRFs
that are filtered to produce only “soft” x-rays). These latter types of machines can
lead to some of the most potentially dangerous exposures because rather than pass
through the body and associated soft tissue these lower energy rays are absorbed in
the skin leading to high skin doses and associated skin damage. In fact, most recorded
human radiation overexposures from analytical x-ray equipment are from damaging low
energy x-ray effects in live layers of skin and shallow tissues.
For obvious reasons, most tissue damage caused by x-ray exposure is to the hands.
For x-ray photons ranging from 5-30 KeV, irradiation of the fingers or hands deposits
most of the damaging energy in shallow tissues from the epidermis to the outer layer
of the bones of the fingers. Due to the photoelectric effect, the x-ray photons entering
the skin are essentially converted to electrons with approximately the same kinetic
energy as the initial x-ray photons. These photoelectrons can further travel and transport
into live soft tissues. Thus, the majority of the energy of low energy x-rays is deposited
in live soft tissues of the fingers and hands.
Typical visual effects such as erythema (sunburn-like reddening of the skin) are manifest
at as little as 50-100 rem of dose equivalent low energy x-ray delivered to the skin
almost immediately after the exposure. At high intensity exposures of low energy x-rays,
acute skin damage similar to thermal burns occurs. Very high exposures may necessitate
skin grafts and/or amputation of fingers and possibly portions of the hands.
To illustrate the table below provides typical beam Dose Rates in machines operating
at 15 kVp vs. 50 kVp tube voltage for hand held units
|Quantity (United States)
||Dose Rate 15kVp max setting (rem/hr)
||Dose Rate 50 kVp max setting (rem/hr)
|Deep Dose Equivalent
|Shallow Dose Equivalent (US NRC Definition)
Note that at 15 kVp maximum as quoted by the manufacturer’s representative results
in the majority of the dose (251 rem/hr) being deposited in the live layers of skin.
The higher energy of 50 kVp is actually less damaging to the skin than the 15 kVp
setting since only 40 rem/hr of the 50 kVp energy is deposited in the live layers
of the skin.
In addition, sales representatives and manufacturer’s tend to obscure the fact that
the 15 kVp instrument above is not a regulatory “exempt” x-ray device and so it must
be registered with state regulators and attached to the OSU permit just as any other
device designed to emit x-rays is, even if it is delivered on loan or donated as a
demonstration model. Finally note that there are documented cases of persons having
lost fingers and significant portions of hands by placing their hands directly in
a “low-energy” X-ray diffraction machine beam for less than one second.
Thus, in order to maintain compliance with state regulations, the Radiation Safety
Office must be made aware of any radiation producing equipment that comes to this
campus for any length of time prior to its operation.
If you have any questions or intend to acquire or use a low energy or portable hand
held x-ray device, including demonstration models of a hand held analytical x-ray
unit(s), please call the Radiation Safety Officer at 405.744.7890 in order to gain
the required authorization and training prior to ordering or acquiring a permanent
or demonstration unit.
Finally, please notify the RSO if you plan to hold a demonstration of a low energy
or portable hand held x-ray device on campus, even if the demonstration will be provided
by a licensed representative or other person(s).