Gamma-H2AX formation in blood cells after thyroid cancer therapy with I-131

Objectives The aim of the study was to investigate the induction, persistence and the decay behaviour of γ-H2AX DNA damage foci in patients with differentiated thyroid carcinoma (DTC).

Methods We investigated 25 patients (7m, 18f, age 42±13) scheduled for ablation therapy. Peripheral blood samples and external dose rate data were obtained between 2h and 144h after administration of I-131 (3.5±0.6 GBq I-131). The dosimetry was performed according to the EANM SOP for pre-therapeutic dosimetry in DTC therapy. The average frequency of γ-H2A.X foci/nucleus was derived from mononuclear peripheral blood lymphocyte samples.

Results The mean absorbed dose to the blood was 0.39±0.40 Gy (Min: 0.17 Gy, Max: 2.2 Gy). After 24h the mean daily dose increment was less than 0.05 Gy. The mean number of γ-H2A.X excess foci/nucleus increased after therapy and reached a maximum of 0.294±0.188 at 2h (20 patients; baseline value: 0.004±0.003) and declined thereafter. Significantly elevated numbers of excess foci/nucleus (0.043±0.032) were still present 144h after therapy. Although the inter-patient variability of excess foci/nucleus numbers per absorbed dose was high, there was a good correlation between the number of excess foci/nucleus and the increment of the absorbed dose for individual patients with >= 4 samples.

Conclusions We consider the γ-H2AX method to be suited for the detection of radiation exposure after incorporation of radionuclides even for absorbed doses to the blood of less than 20 mGy.