ESTRO 2023 - Abstract Book

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ESTRO 2023

Results Loss of total tissue area, reduced adipose tissue fraction, increased epidermal thickness and almost complete skin adnexa ablation were all characteristics of the irradiated legs. Histological representatives are presented in Figure 1. Generally, the fraction of connective tissue was primarily increased in the upper leg sections, whereas loss of adipose tissue and total tissue area was observed in upper leg and the joint as well. The most severe changes were seen in the epidermal thickness and almost total ablation of the skin adnexa across all three sections. Mice with the most severe degree (score 4) in the functional joint flexibility assay also possessed most structural alterations.

Conclusion Fundamental structural changes occur in mice legs post proton therapy. Clinical findings of leg atrophy (loss of total area and hair) and decreased flexibility could be visualized and quantified using stereology assisted histopathology. Evaluation in a larger study with stratification according to radiation dose is needed to investigate if a dose-response relationship can be supported histologically. The tested procedure for histological examination was found to be technically feasible and is expected to produce a robust pathological comparison to a functional leg contraction assay for radiation-induced late effects assessment in vivo .

PO-2206 Radiopathological consequences of low energy X-rays overexposures: a dose effect study

M. Guillou 1 , B. L'Homme 1 , F. Trompier 2 , A. Errabii 1 , G. Gruel 1 , Y. Prezado 3 , M. Dos Santos 1

1 IRSN, SERAMED / LRACC, Fontenay-aux-Roses, France; 2 IRSN, SDOS / LDRI, Fontenay-aux-Roses, France; 3 Institut Curie, Inserm U 1021-CNRS UMR 3347, Orsay, France Purpose or Objective 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. Materials and Methods 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. Results 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.