18F-FDG PET/CT scanning: Biological effects on patients: Entrance surface dose, DNA damage, and chromosome aberrations in lymphocytes.

Positron Emission Tomography/Computed Tomography (PET/CT), a combination of PET and CT, is used in tumor staging, therapy planning, and treatment response monitoring. During PET imaging, patients receive low doses of radiation, which can induce an adaptive response and necessitate higher doses for therapeutic efficacy. Higher doses may augment toxicity to normal cells. We are examining the effects of short-term, low-dose exposures to ionizing radiation. Entrance Surface Dose (ESD) to head, shoulders, and pelvis regions were measured using Li2B4O7: Mn thermoluminescent dosimeters. Induced DNA damage in lymphocytes was measured using γ-H2AX, p53Ser-15, chromosome aberrations, and micronucleus formation in subjects (n = 25) who underwent 18F-FDG PET/CT. The mean ESD ± SD value obtained were 32.40 ± 16.86, 32.58 ± 14.22, 32.02 ± 15.42, 43.55 ± 18.25 and 42.80 ± 24.67 mGy for the head, right shoulder, left shoulder, right pelvic, and left pelvic regions, respectively. The effective doses of PET and CT ranged from 4.01 to 6.61 and 16.40-72.18 mSv, respectively, and the obtained Dose Length Product (DLP) varied from 1093 to 4812 mGy*cm. There was no correlation between DLP and ESD (r2 = 0.1). The chromosome aberration assay showed a significant increase (p < 0.05), post-scanning vs. pre-scanning; the γ-H2AX, p53Ser-15, and micronucleus assays did not show significant increases. Induced DNA damage showed inter-individual variation among the study subjects. Our results imply that the patients received a biologically significant dose during 18F-PET/CT scanning and precautions may be needed to reduce any long-term risk of exposure.

Entrance surface dose and induced DNA damage in blood lymphocytes of patients exposed to low-dose and low-dose-rate X-irradiation during diagnostic and therapeutic interventional radiology procedures.

The ionizing radiation received by patients and health workers due to radiological imaging may increase the risks of radiation effects, such as cancer and cataracts. We have investigated the dose received by specific areas around the head and related this to DNA damage in the blood lymphocytes of subjects exposed to interventional imaging. The entrance surface doses (ESD) to the forehead, neck, and shoulder were measured with a thermoluminescence dosimeter (CaSO4 disc or polycrystalline powder of lithium tetraborate doped with Mn) and compared with that of dose area product (DAP). DNA damage was measured by γ-H2AX, p53ser15, chromosomal aberration (CA), and micronucleus (MN) assays in lymphocytes of patients (n=75), before and 2 and 24h after exposure. The measured ESD values were 230.5±4.9, 189.5±3.55 and 90.7±3.4mGy for the forehead, neck, and shoulder, respectively. The DAP varied from 1.8 to 2047 Gy*cm2, showing a correlation with fluoroscopy time (r=0.417). Received doses did not increase early markers of DNA damage (γ-H2AX and p53ser15 assays), but residual damage (CA and MN frequencies) showed a significant (p<0.001) increase at 2 and 24h post-exposure compared to pre-imaging, despite poor correlation with DAP (r=0.1). Our results show that interventional imaging procedures deliver significant radiation doses and induce measurable DNA damage in lymphocytes of subjects, highlighting the need for rigorous patient safety protocols.

Assessment of dose and DNA damages in individuals exposed to low dose and low dose rate ionizing radiations during computed tomography imaging.

PURPOSE: Computed tomography (CT) is a frequently used imaging modality that contributes to a tenfold increase in radiation exposure to the public when compared to other medical imaging modalities. The use of radiation for therapeutic need is always rationalized on the basis of risk versus benefit thereby increasing concerns on the dose received by patients undergoing CT imaging. Therefore, it was of interest to us to investigate the effects of low dose and low dose-rate X-irradiation in patients who underwent CT imaging by recording the doses received by the eye, forehead and thyroid, and to study the levels of damages in the lymphocytes in vivo. MATERIALS AND METHODS: Lithium manganese borate doped with terbium (LMB:Tb) thermo luminescence dosimeters (TLD) were used to record the doses in the patient's (n = 27) eye, forehead, and thyroid and compared with the dose length product (DLP) values. The in vivo DNA damages measured were compared before and after CT imaging using chromosomal aberration (CA) and micronucleus (MN) assays. RESULTS: The overall measured organ dose ranged between 2 ± 0.29 and 520 ± 41.63 mGy for the eye, 0.84 ± 0.29 and 210 ± 20.50 mGy for the forehead, and 1.79 ± 0.43 and 185 ± 0.70 mGy for the thyroid. The in vivo damages measured from the blood lymphocytes of the subjects showed an extremely significant (p < 0.0001) increase in CA frequency and significant (p < 0.001) increase in MN frequency after exposure, compared to before exposure. CONCLUSION: The results suggest that CT imaging delivers a considerable amount of radiation dose to the eye, forehead, and thyroid, and the observed increase in the CA and MN frequencies show low dose radiation effects calling for protective regulatory measures to increase patient's safety. This study is the first attempt to indicate the trend of doses received by the patient's eye, forehead and thyroid and measured directly in contrast to earlier values obtained by extrapolation from phantoms, and to assess the in vivo low dose effects in an Indian patient population undergoing CT procedures.