Spectral energy effects in ESR bone dosimetry: photons and electrons

Preclinical modeling of low energy X-rays radiological burn: Dosimetry study by monte carlo simulations and EPR spectroscopy

Interventional radiology has grown considerably over the last decades and become an essential tool for treatment or diagnosis. This technique is mostly beneficial and mastered but accidental overexposure can occur and lead to the appearance of deterministic effects. The lack of knowledge about the radiobiological consequences for the low-energy X-rays used for these practices makes the prognosis very uncertain for the different tissues. In order to improve the radiation protection of patients and better predict the risk of complications, we implemented a new preclinical mouse model to mimic radiological burn in interventional radiology and performed a complete characterization of the dose deposition. A new setup and collimator were designed to irradiate the hind legs of 15 mice at 30 Gy in air kerma at 80 kV. After irradiation, mice tibias were collected to evaluate bone dose by Electron Paramagnetic Resonance (EPR) spectroscopy measurements. Monte Carlo simulations with Geant4 were performed in simplified and voxelized phantoms to characterize the dose deposition in different tissues and evaluate the characteristics of secondary electrons (energy, path, momentum). 30 mice tibias were collected for EPR analysis. An average absorbed dose of 194.0 ± 27.0 Gy was measured in bone initially irradiated at 30 Gy in air kerma. A bone to air conversion factor of 6.5 ± 0.9 was determined. Inter sample and inter mice variability has been estimated to 13.9%. Monte Carlo simulations shown the heterogeneity of the dose deposition for these low X-rays energies and the dose enhancement in dense tissue. The specificities of the secondary electrons were studied and showed the influence of the tissue density on energies and paths. A good agreement between the experimental and calculated bone to air conversion factor was obtained. A new preclinical model allowing to perform radiological burn in interventional radiology-like conditions was implemented. For the development of new preclinical radiobiological model where the exact knowledge of the dose deposited in the different tissues is essential, the complementarity of Monte Carlo simulations and experimental measurements for the dosimetric characterization has proven to be a considerable asset.

The Chernobyl accident: EPR dosimetry on dental enamel of children

The radiation dose on tooth enamel of children living close to Chernobyl has been evaluated by EPR. The sample preparation was reduced to a minimum of mechanical steps to remove a piece of enamel. A standard X-ray tube at low energy was used for additive irradiation. The filtration effect of facial soft tissue was taken into account. The radiation dose for a group of teeth slightly exceeds the annual dose, whereas for another group the dose very much exceeds the annual dose. Since the higher dose is found in teeth whose enamel have much lower EPR sensitivity to the radiation, it can be suggested that for these teeth the native signal could alter the evaluation of the smaller radiation signal.

ESR dosimetry of 89Sr and 153Sm in bone

The radiation absorbed dose in the rabbit bone delivered by 153Sm-EDTMP (samarium ethylenediaminetetra methylene diphosphonic acid) and 89SRCl2 (strontium chloride) was measured by means of electron spin resonance (ESR). These radioisotopes are used in systemic radiotherapy for palliation of painful bone metastases. The knowledge of the dose is important in order to avoid side effects to the bone marrow. The ESR radiation dose signal was calibrated by the additive dose method using cobalt-60 gamma rays. For 153Sm-EDTMP, the bone doses in three rabbits were (4 +/- 2), (5 +/- 1) and (5 +/- 2) cGy kg/MBq. For 89SrCl2, a dose of (2 +/- 1) cGy kg/MBq was found in one rabbit.

Radiation dosimetry of an accidental overexposure using EPR spectrometry and imaging of human bone

On 11 December 1991 a radiation accident occurred at an industrial accelerator facility. A description of the facility and details of the accident are reported in Schauer et al., 1993a). In brief, during maintenance on the lower window pressure plate of a 3 MV potential drop accelerator, an operator placed his hands, head, and feet in the radiation beam. The filament voltage of the electron source was turned 'off', but the full accelerating potential was on the high voltage terminal. The operator's body, especially his extremities and head, were exposed to electron dark current. At approx. 3 months post-irradiation, the four digits of the victim's right hand and most of the four digits of his left hand were amputated. Electron paramagnetic resonance (EPR) spectrometry was used to estimate the radiation dose to the victim's extremities. Extremity dose estimates ranged from 55.0 Gy (+/- 4.7 Gy) to 108 Gy (+/- 24.1 Gy).