FY 2001 Radiation Bio-Effects
- Responses of Human Skin to Ultraviolet Radiation
- Sunlamps and Sunbeds: Scientific and Regulatory Issues
- Ultrasonic Characterization of Skin Following Ultraviolet Light Exposures
This program encompasses a collection of biological research projects needed to ensure that the public enjoys the benefits of modern medical and consumer technology without undue harm due to associated radiation exposures. Another goal of the program is to prevent unnecessary exposure of the population to radiation emitted from electronic products and to establish the scientific basis for regulatory decisions involving electronic product radiation.
The projects described below are complimented by standards development activities, particularly in the areas of nonionizing radiation exposures. The OST scientists responsible for this research are active in the revision of international standards and guidelines for ultraviolet, radio frequency, and extremely low frequency radiation.
Boron Neutron Capture Therapy (BNCT) promises the potential of becoming a major new modality for the treatment of brain tumors, whose therapy is currently problematic. Its clinical investigation and commercialization will raise a number of new medical device and drug-device issues for CDRH and CDER. OST has worked toward developing computational capabilities to verify dosimetric data submitted in IDEs and PMAs. One of the current challenges to bringing BNCT to the clinic is the design of epithermal neutron beams which will result in safer and more effective therapy by maximizing tumor dose while minimizing normal tissue dose. Since reactor neutron sources are unsuitable for siting in hospitals, there is a need for computational design of beam generators employing particle accelerators. This requires extensive modeling of combinations of charged particle neutron sources, moderators, and reflectors to optimize the dose delivered to a tumor mass. Variables to be considered include tumor dose for various tissue depths and dose to normal tissues from boron capture, as well as proton recoil and nitrogen capture reactions and capturing gamma rays from the target structure. These calculations will provide guidance on desirable properties of neutron beams proposed for IDE's and can serve as a basis for the design of a future experimental facility. Until recently, powerful neutron sources were limited to a very few locations at existing nuclear reactors and thus not generally available for patient treatment. The marketing of a new generation of powerful nuclear particle accelerators, comparable in price to the accelerators currently used for radiation therapy, will soon make clinically useful neutron sources available for therapeutic applications.
Currently over 100 million Americans use wireless phones. This exposure of large numbers of people to radio-frequency radiation (RFR) is unprecedented. Data relating to the safety of wireless phones is currently inadequate to determine whether adverse health effects are likely to result from these exposures. A small number of chronic rodent exposures have been conducted which show no evidence of cancer in exposed animals; but one of these studies did indicate an increased number of lymphomas in susceptible transgenic mice. In addition, in vitro studies have been reported to show changes in enzyme activities that are suggestive of cancer-promoting effects. Another in vitro study showed an increase in micronucleus formation, a possible marker for epigenetic effects on DNA synthesis, in human cells exposed to wireless phone emissions. Research into the bio-effects and effects on medical electronics of cell phone use continues. OST developed and established a cooperative research agreement allowing FDA to better assess the possible health risks associated with mobile phone technology. Once the mobile phone industry has initiated this research, FDA will provide ongoing scientific and technical oversight of the research programs. OST research investigated some of the reported in vitro effects using an exposure system calibrated in terms of specific absorption rate. This research, along with extensive involvement in research with other laboratories, aids assessing published data that suggest the biological effects of exposure to radio-frequency radiation at levels relevant to wireless phone use.
OST studies of the utility of novel noninvasive and biomarker methods to test and standardize skin responses to ultraviolet radiation (UV) can provide data needed for revising the national and international standards in the area. Such research supports CDRH policies for ultraviolet lamps used in medicine and cosmetology, CDER policies related to sunscreens and photosensitizing drugs, and CFSAN policies in the area of cosmetics. FDA's policies regarding sunlamps have been repeatedly questioned by the consumers, the industry, and the medical community. OST research will include the collection of data on human subjects representing skin types I-VI and racial ethnic groups of (1) American Indians or Alaska Natives, (2) Black or African Americans, (3) Asians, (4) Hispanic or Latinos, (5) Native Hawaiians or Other Pacific Islanders, and (6) Whites. These data include changes in the skin properties following UV exposure assessed using two mechanical methods, four optical methods, one ultrasound method, and several biomarkers measured in the biopsies. OST data provide a solid scientific basis for improving the classification and testing of human skin sensitivity to UV.
Some UV-exposed skin cells do not die. Rather they acquire genetic mutations that can lead to skin cancer. Inhibition or failure of cells to die when too many genetic mutations have been acquired has recently been implicated as a mechanism for initiation and promotion of skin cancer by UV. In vitro laboratory data from cell exposure to UVA and UVB wavelengths separately, which are both emitted to different degrees from tanning lamps and, together, can be used to establish adjustments that should be made to existing UV risk assessment equations. Until recently, no risk assessment of tanning lamps for skin cancer could be accurately performed because only the action spectrum, i.e., data for the individual UV wavelengths, was known. The combined output effect on skin cancer from tanning lamps, i.e., UVA and UVB wavelengths, could not be established because a definitive biological endpoint to monitor in human cells was not established. OST data can be used to see if an additive, synergistic, or antagonistic effect occurs when UVA and UVB are combined together, as they are in tanning device emission. With this data, scientists will be able to complete a risk assessment because they will know the appropriate approach and equations to use in this tanning lamp situation.
Radiation scientists are assessing the utility of several testing methods for characterizing the effects of UV radiation on skin for potential use in the regulation of products such as sunlamps, tanning booths, sunscreens, and photosensitizing drugs. In addition, a cross-agency effort was started to estimate the effect of exposure to ultraviolet radiation and implement methods to reduce exposures. The studies, initially funded by grants from the FDA Office of Science have begun to yield results that are useful in developing standards for determining UV exposures and for validating predictive models of tissue behavior when exposed to UV.
Key words: UV, tanning, melanin
OST is investigating the effects of UV exposure on human skin to update standards for UV-emitting/transmitting products. These studies involve exposing small areas of the backs of volunteers to single or repeated exposures and a broad range of measurements. Typical dermatological and tanning sources are used. OST has collected data on 93 subjects to date. The results indicate that melanin content may not be a sole factor in determining the UV sensitivity of human skin. Also, OST scientists demonstrated that both DNA repair and melanin production are more efficient in UV-resistant subjects than in UV-sensitive subjects. This indicates that DNA damage may not be a sole melanogenesis-stimulating factor. Preliminary data from the repeated exposure study indicate that UV burden to tanners can be markedly reduced without compromising the desired effect. These and other results of biomarker and noninvasive measurements provide quantitative data that will replace outdated standard criteria and guidelines.
Key words: sunlamps, sunbeds, melanoma
A review of CDRH’s work on sunlamps was published in the book Sun Protection in Man (2001). This article discussed safety and regulatory issues related to sunlamps and sunbeds. The focus is on the indoor tanning industry within the United States, current U.S. and international regulations, possible changes to U.S. regulations, an assessment of the science base for regulatory changes, and a description of some of the U.S. and international standards organizations that are heavily involved with UV research and regulations.
The U.S. Food and Drug Administration is considering changes to its regulations that involve the content and design of its warning labels, redefining who is a manufacturer, updating the recommended exposure schedule, updating the value of minimal erythemal dose (MED), and possibly using the non-melanoma cancer action spectrum for calculating recommended annual dose limits.
Key words: ultrasound, high-frequency, UV, skin exposure, exposure measurements.
The incidence of skin cancer is increasing in the U.S. and is attributed to the cumulative damage from repeated sunburns induced by the ultraviolet (UV) component of sunlight. While the link between cancer and sunlight is strong, the ability to predict any given individual’s susceptibility to UV-induced skin damage is very limited. This study is a component of on-going work involving OST researchers to try to reduce that predictive uncertainty.
CDRH laboratories have used high-frequency (20 MHz) ultrasound imaging to measure changes in skin structure after exposure to UV radiation. Measurements were obtained on exposed and non-exposed areas of skin following a graduated series of known UV exposures. Ultrasound images were obtained immediately after exposure and at several time points during the healing interval. Initial data analysis found changes in the dermal thickness properties of the skin. A new phase of the study is being conducted and includes a larger number of subjects and data samples per subject. The results are promising but warrant further study. This work is part of a CDRH effort to find new approaches for evaluating the safety and efficacy of UV-emitting products regulated by FDA.