Session Item

Low-energy X-rays (< 100kV) are widely used in the medical field, especially for imaging, interventional radiology or radiotherapy. At low-energy, the photoelectric effect being dominant, the absorbed dose is very heterogeneous and depends much on the materials density. The lack of knowledge about the biological consequences at low-energy, due to the heterogeneity of dose deposition, makes the prognosis very uncertain especially when severe deterministic effects appear (radiological burns). Characterizing the biological effects is essential to improve patient management.

A new preclinical model of localized paw mouse exposition was implemented on the SARRP at 80kV, allowing to mimic the low-energy exposures to normal tissues. Dosimetric measurements, both experimental by EPR spectroscopy (bone dose) and simulated on Geant4 were performed to determine the dose absorbed to the different tissues (bone, muscle and marrow). Animals were irradiated with different dose (Kair=15, 30 or 45Gy) to mimic different lesion intensity and are followed overtime, to 84-day post-irradiation by lesion scoring to assess their severities, weight, laser Doppler images to measure blood flow and complete blood count evolution. MicroCT and histological analyses on bone and muscle allow to characterize and quantify radio-induced lesions.

The skin dose is approximatively the same than the dose administered in Kair but the bone and marrow dose are estimated to be respectively 7 and 1.5 times higher. A good agreement was found between experimental and simulated dosimetry measurements for the bone dose estimation (relative gap 12%).  All protocols reach a lesion peak 21 days post-irradiation of increasing intensity with dose, correlated with weight loss, and increase of blood flow, then a total to partial healing depending on dose. The lesion follow-up allows to classify the exposure protocols according to the lesion severity. Thus, the 15 Gy protocol leads to a light lesion, contrary to the 30 and 45 Gy protocols leading to severe lesions. A decrease (44% compared to non-irradiated mice) in lymphocytes is highlighted by the complete blood count. Concerning bone architecture, a loss of trabecular bone volume (30% at lesion peak) and a significant change in the chondrocytes organization at the epiphyseal line are shown by microCT and histological analysis respectively.

This new preclinical model allows to mimic different degrees of radio-induced lesions severity at low energy, depending on the irradiation dose (Kair). For this type of exposition, where the dose distribution is very heterogeneous, the dosimetric characterization is a considerable asset to better understand the biological consequences on different normal tissues. The radiopahtological study allows to characterize the radio-induced lesions in function of the dose and the tissue considered aiming to improve the management of patients and the prediction of the risk of complications following accidental overexposure.