Beyond Simple Exposures
Historically, biodosimetry studies focused exclusively on external whole-body photon irradiation. The main theme of our center is to assess the significance of the variety of other radiation scenarios that are likely to occur, using all the endpoints under study. These scenarios are:
How will the results of the biodosimetric assays change with prolonged exposure time, over periods up to at least 24 hours, compared with acute exposure?
In order to enable low dose-rate studies, we have modified our X-RAD 320 x-ray irradiator to provide essentially the same spectrum of X rays at dose rates ranging from 4 Gy/day to 1 Gy/min. We have designed and built a custom incubator (Figure) to allow prolonged exposure of blood samples under physiological conditions. We have also designed and built a custom mouse housing unit and installed a cooling and air exchange system within the x-ray chamber, to maintain appropriate conditions for long-term exposure of mice. We currently plan to extend the range of dose rates available for our studies, both to very high dose-rates and to much more protracted low dose rates.
The direct radiation component of an Improvised Nuclear Device (IND) exposure will be at much higher dose rates than the ~1 Gy/min rates that are typically available from conventional irradiators. To approach a more realistic dose rate for this scenario, we will build a high dose rate (up to 120 Gy / min) mouse irradiation system based on a radiotherapy linear accelerator.
At the other end of the spectrum, we plan to extend our studies of low dose rate effects using a variable-dose-rate external 137Cs irradiator (VADER), which we have designed to be able to simulate the changing dose rates experienced when 137Cs has been internally deposited and is slowly excreted from the body. We will also be able to use this device to provide a constant low dose rate to mice housed within the irradiator for weeks.
At RARAF, we have long had facilities to provide monoenergetic neutron irradiations, both in vitro and for small animals. We have now developed and tested a unique facility to simulate the neutron spectra at relevant distances (e.g. 1.5 km) from the epicenter of a nuclear detonation. This new facility has been and continues to be used by all three projects. As expected an increased RBE has been seen over photon irradiations. In addition, we have an x-ray machine located in the next room to the neutron irradiation room, which allows x-ray irradiations to be performed immediately before or after neutron irradiation, for simulating combined exposures, which is the current focus of these studies.
A major component of the absorbed dose from a Radiological Dispersal Device (RDD) or nuclear detonation will be from the incorporation of radionuclides into the body, either by inhalation of radioactive aerosols or ingestion of contaminated food. In order to study the impact of internal emitters on our biodosimetric methods, we have previously partnered with the Lovelace Respiratory Research Institute where two prior studies were concluded on the effects of internalized emitters:
- Cs-137: a typical gamma emitter that provides a uniform total body exposure with an exponentially decaying dose rate.
- Sr-90: a beta emitter that is accumulated in the bone providing total body irradiation with a constant dose rate.
Some data from these studies are presented in the results section of Projects 1, 2 and 3.
Currently studies are underway with the VADER lose dose irratiation platform will allow us to follow up further on these studies including additional dose-rates and endpoints without the need for injection/inhalation for the animals. This reduces radioacitve waste and the need for specialized radioactive animal handling.