DNA Damage in Blood Leukocytes of Prostate Cancer Patients Undergoing PET/CT Examinations with [68Ga]Ga-PSMA I&T

The Influence of Computed Tomography Contrast Agent on Radiation-Induced Gene Expression and Double-Strand Breaks

After nuclear scenarios, combined injuries of acute radiation syndrome (ARS) with, e.g., abdominal trauma, will occur and may require contrast-enhanced computed tomography (CT) scans for diagnostic purposes. Here, we investigated the effect of iodinated contrast agents on radiation-induced gene expression (GE) changes used for biodosimetry (AEN, BAX, CDKN1A, EDA2R, APOBEC3H) and for hematologic ARS severity prediction (FDXR, DDB2, WNT3, POU2AF1), and on the induction of double-strand breaks (DSBs) used for biodosimetry. Whole blood samples from 10 healthy donors (5 males, 5 females, mean age: 28 ± 2 years) were irradiated with X rays (0, 1 and 4 Gy) with and without the addition of iodinated contrast agent (0.016 ml contrast agent/ml blood) to the blood prior to the exposure. The amount of contrast agent was set to be equivalent to the blood concentration of an average patient (80 kg) during a contrast-enhanced CT scan. After irradiation, blood samples were incubated at 37°C for 20 min (DSB) and 8 h (GE, DSB). GE was measured employing quantitative real-time polymerase chain reaction. DSB foci were revealed by γH2AX + 53BP1 immunostaining and quantified automatically in >927 cells/sample. Radiation-induced differential gene expression (DGE) and DSB foci were calculated using the respective unexposed sample without supplementation of contrast agent as the reference. Neither the GE nor the number of DSB foci was significantly (P = 0.07-0.94) altered by the contrast agent application. However, for some GE and DSB comparisons with/without contrast agent, there were weakly significant differences (P = 0.03-0.04) without an inherent logic and thus are likely due to inter-individual variation. In nuclear events, the diagnostics of combined injuries can require the use of an iodinated contrast agent, which, according to our results, does not alter or influence radiation-induced GE changes and the quantity of DSB foci. Therefore, the gene expression and γH2AX focus assay can still be applied for biodosimetry and/or hematologic ARS severity prediction in such scenarios.

Postirradiation temperature influences DSB repair and dicentric chromosome formation-potential impact for dicentric chromosome analysis in interlaboratory comparisons

The objective was to investigate the influence of different pre-storage temperatures in the dicentric chromosome analysis (DCA) protocol (22°C vs. 37°C) by using γ-H2AX + 53BP1 foci as a marker for deoxyribonucleic acid (DNA) double-strand break (DSB) damage induction and repair and the formation of dicentric chromosomes as a result of mis-repair. Repair of γ-H2AX + 53BP1 DSB foci was absent in samples that were incubated for 2 h at 22°C after exposure of 0.5 and 1.2 Gy. When 0.5- and 1.2-Gy-exposed samples were incubated at 37°C for 2 h, there was an average decline of 31 and 52% of DSB foci, respectively. This indicated that DNA repair occurred. There was a 27% decrease in dicentric chromosome yield at 1.2 Gy and a 15% decrease at 3.5 Gy after post-irradiation incubation for 2 h at 37°C relative to the observed dicentric frequencies at 22°C. Recommended to re-phase: our data suggested that there were more open DSBs after a 2-h incubation at 22°C, which contributed to more mis-repair and dicentric formation from the start of culture. Our findings are corroborated by publications showing that lesion interaction based on enzymatic activity is suppressed below 21°C. As such temperature variations can be a source of variation in DCA during interlaboratory comparison studies, we propose to establish a common guide for the standardisation of pre-culture conditions in cytogenetic dosimetry proficiency testing.

Ex-vivo dose response characterization of the recently identified EDA2R gene after low level radiation exposures and comparison with FDXR gene expression and the γH2AX focus assay

OBJECTIVE

Recently, promising radiation-induced EDA2R gene expression (GE) changes after low level radiation could be shown. Stimulated by that, in this study, we intended to independently validate these findings and to further characterize dose-response relationships in comparison to FDXR and the γH2AX-DNA double-strand break (DSB) focus assay, since both assays are already widely used for biodosimetry purposes.

MATERIALS AND METHODS

Peripheral blood samples from six healthy human donors were irradiated ex vivo (dose: ranging from 2.6 to 49.7 mGy). Subsequently, the fold-differences relative to the sham irradiated reference group were calculated. Radiation-induced changes in GE of FDXR and EDA2R were examined using the quantitative real-time polymerase-chain-reaction (qRT-PCR). DSB foci were quantified in 100 γH2AX + 53BP1 immunostained cells employing fluorescence microscopy. Examinations were performed at single time points enabling sufficient detection of both endpoints.

RESULTS

A significant increase in EDA2R GE relative to the unexposed control was observed in the range of 2.6 mGy (1.6-fold, p = .045) to 5.4 mGy (2.2-fold, p = .0002), whereas the copy numbers increased linearly up to 13.1-fold at 49.7 mGy. On the contrary, FDXR upregulation (2.2-fold) became significant after a 22.6 mGy exposure (p ≤ .02) and increased linearly up to 4-fold at 49.7 mGy. A significant increase in radiation-induced foci (relative to unexposed, RIF-fd) was observed after 11.3 mGy (RIF-fd: 1.5 ± 0.5, p ≤ .03), while the foci increased linearly up to 3-fold at 49.7 mGy. From this, the FDXR and RIF-fd slopes have shown comparability, while the EDA2R slope was five times higher. Nevertheless, the coefficient of variation (CV) of EDA2R was about 30% higher than for RIF-fd.

CONCLUSION

Higher radiation-induced EDA2R GE changes and a lower radiation detection level compared to RIF-fd and FDXR GE changes examined under optimal conditions ex vivo on human samples appear promising. Yet, our results represent just the beginning of further studies to be conducted in animal models for further time- and dose-dependent evaluation and additional examinations on radiologically examined patients to evaluate the impact of confounder, such as age, sex, social behavior, or diseases.

Initial experience on abdominal photon-counting computed tomography in clinical routine: general image quality and dose exposure

OBJECTIVES

Photon-counting computed tomography has lately found its way into clinical routine. The new technique could offer substantial improvements regarding general image quality, image noise, and radiation dose reduction. This study evaluated the first abdominal examinations in clinical routine and compared the results to conventional computed tomography.

METHODS

In this single-center retrospective study, 66 patients underwent photon-counting and conventional abdominal CT. Four radiologists assessed general image quality, image noise, and image artifacts. Signal-to-noise ratio and dose properties of both techniques within the clinical application were compared. An ex vivo phantom study revealed the radiobiological impact by means of DNA double-strand break foci in peripheral blood cells by enumerating γ-H2AX+53BP1 foci.

RESULTS

General image quality in accordance with the Likert scale was found superior for photon-counting CT (4.74 ± 0.46 vs. 4.25 ± 0.54; p < 0.001). Signal-to-noise ratio (p < 0.001) and also dose exposure were higher for photon-counting CT (DLP: 419.2 ± 162.2 vs. 372.3 ± 236.6 mGy*cm; p = 0.0435). CT exposure resulted in significantly increased DNA damage in comparison to sham control (p < 0.001). Investigation of the average foci per cell and radiation-induced foci numbers revealed significantly elevated numbers (p = 0.004 and p < 0.0001, respectively) after photon-counting CT.

CONCLUSION

Photon-counting CT in abdominal examinations showed superior results regarding general image quality and signal-to-noise ratio in clinical routine. However, this seems to be traded for a significantly higher dose exposure and corresponding double-strand break frequency. Optimization of standard protocols in further clinical applications is required to find a compromise regarding picture quality and dose exposure.

KEY POINTS

• Photon-counting computed tomography promises to enhance the diagnostic potential of medical imaging in clinical routine. • Retrospective single-center study showed superior general image quality accompanied by higher dose exposure in initial abdominal PCCT protocols compared to state-of-the-art conventional CT. • A simultaneous ex vivo phantom study revealed correspondingly increased frequencies of DNA double-strand breaks after PCCT.

An evaluation of DNA double strand break formation and excreted guanine species post whole body PET/CT procedure

Ionizing radiation-induced oxidation and formation of deoxyribonucleic acid (DNA) double strand breaks (DSBs) are considered the exemplar of genetic lesions. Guanine bases are most prone to be oxidized when DNA and Ribonucleic acid (RNA) are damaged. The repair processes that are initiated to correct this damage release multiple oxidized guanine species into the urine. Hence, the excretion of guanine species can be related with the total repair process. Our study quantified the total DSBs formation and the amount of guanine species in urine to understand the DNA break and repair process after whole body (WB) exposure to 18F-FDG positron emission tomography/computed tomography (PET/CT). A total of 37 human participants were included with control and test groups and the average radiation dose was 27.50 ± 2.91 mSv. γ-H2AX foci assay in the collected blood samples was performed to assess the DSBs, and excreted guanine species in urine were analyzed by a competitive ELISA method. We observed a significant increase of DNA damage that correlated well with the increasing dose (p-value 0.009) and body weight (p-value 0.05). In the test group, excreted guanine species in urine sample significantly increased (from 24.29 ± 5.82 to 33.66 ± 7.20 mg/mmol creatinine). A minimum (r2 = 0.0488) correlation was observed between DSBs formation and excreted guanine species. A significant difference of DNA damage and 8-OHdG formation was seen in the test group compared to controls. Larger population studies are needed to confirm these observations, describe the fine-scale timing of changes in the biomarker levels after exposure, and further clarify any potential risks to patients from PET/CT procedures.

Gene expression changes and DNA damage after ex vivo exposure of peripheral blood cells to various CT photon spectra

Dual-energy CT provides enhanced diagnostic power with similar or even reduced radiation dose as compared to single-energy CT. Its principle is based on the distinct physical properties of low and high energetic photons, which, however, may also affect the biological effectiveness and hence the extent of CT-induced cellular damage. Therefore, a comparative analysis of biological effectiveness of dual- and single-energy CT scans with focus on early gene regulation and frequency of radiation-induced DNA double strand breaks (DSBs) was performed. Blood samples from three healthy individuals were irradiated ex vivo with single-energy (80 kV and 150 kV) and dual-energy tube voltages (80 kV/Sn150kV) employing a modern dual source CT scanner resulting in Volume Computed Tomography Dose Index (CTDIvol) of 15.79-18.26 mGy and dose length product (DLP) of 606.7-613.8 mGy*cm. Non-irradiated samples served as a control. Differential gene expression in peripheral blood mononuclear cells was analyzed 6 h after irradiation using whole transcriptome sequencing. DSB frequency was studied by 53BP1 + γH2AX co-immunostaining and microscopic evaluation of their focal accumulation at DSBs. Neither the analysis of gene expression nor DSB frequency provided any evidence for significantly increased biological effectiveness of dual-energy CT in comparison to samples irradiated with particular single-energy CT spectra. Relative to control, irradiated samples were characterized by a significantly higher rate of DSBs (p < 0.001) and the shared upregulation of five genes, AEN, BAX, DDB2, FDXR and EDA2R, which have already been suggested as radiation-induced biomarkers in previous studies. Despite steadily decreasing doses, CT diagnostics remain a genotoxic stressor with impact on gene regulation and DNA integrity. However, no evidence was found that varying X-ray spectra of CT impact the extent of cellular damage.

EANM position paper on the role of radiobiology in nuclear medicine

With an increasing variety of radiopharmaceuticals for diagnostic or therapeutic nuclear medicine as valuable diagnostic or treatment option, radiobiology plays an important role in supporting optimizations. This comprises particularly safety and efficacy of radionuclide therapies, specifically tailored to each patient. As absorbed dose rates and absorbed dose distributions in space and time are very different between external irradiation and systemic radionuclide exposure, distinct radiation-induced biological responses are expected in nuclear medicine, which need to be explored. This calls for a dedicated nuclear medicine radiobiology. Radiobiology findings and absorbed dose measurements will enable an improved estimation and prediction of efficacy and adverse effects. Moreover, a better understanding on the fundamental biological mechanisms underlying tumor and normal tissue responses will help to identify predictive and prognostic biomarkers as well as biomarkers for treatment follow-up. In addition, radiobiology can form the basis for the development of radiosensitizing strategies and radioprotectant agents. Thus, EANM believes that, beyond in vitro and preclinical evaluations, radiobiology will bring important added value to clinical studies and to clinical teams. Therefore, EANM strongly supports active collaboration between radiochemists, radiopharmacists, radiobiologists, medical physicists, and physicians to foster research toward precision nuclear medicine.

α-Particle-induced DNA damage tracks in peripheral blood mononuclear cells of [223Ra]RaCl2-treated prostate cancer patients

PURPOSE

One therapy option for prostate cancer patients with bone metastases is the use of [²²³Ra]RaCl₂. The α-emitter ²²³Ra creates DNA damage tracks along α-particle trajectories (α-tracks) in exposed cells that can be revealed by immunofluorescent staining of γ-H2AX+53BP1 DNA double-strand break markers. We investigated the time- and absorbed dose-dependency of the number of α-tracks in peripheral blood mononuclear cells (PBMCs) of patients undergoing their first therapy with [²²³Ra]RaCl₂.

METHODS

Multiple blood samples from nine prostate cancer patients were collected before and after administration of [²²³Ra]RaCl₂, up to 4 weeks after treatment. γ-H2AX- and 53BP1-positive α-tracks were microscopically quantified in isolated and immuno-stained PBMCs.

RESULTS

The absorbed doses to the blood were less than 6 mGy up to 4 h after administration and maximally 16 mGy in total. Up to 4 h after administration, the α-track frequency was significantly increased relative to baseline and correlated with the absorbed dose to the blood in the dose range < 3 mGy. In most of the late samples (24 h - 4 weeks after administration), the α-track frequency remained elevated.

CONCLUSION

The γ-H2AX+53BP1 assay is a potent method for detection of α-particle-induced DNA damages during treatment with or after accidental incorporation of radionuclides even at low absorbed doses. It may serve as a biomarker discriminating α- from β-emitters based on damage geometry.

Detection and Characterization of Musculoskeletal Cancer Using Whole-Body Magnetic Resonance Imaging

Whole-body magnetic resonance imaging (WB-MRI) is gradually being integrated into clinical pathways for the detection, characterization, and staging of malignant tumors including those arising in the musculoskeletal (MSK) system. Although further developments and research are needed, it is now recognized that WB-MRI enables reliable, sensitive, and specific detection and quantification of disease burden, with clinical applications for a variety of disease types and a particular application for skeletal involvement. Advances in imaging techniques now allow the reliable incorporation of WB-MRI into clinical pathways, and guidelines recommending its use are emerging. This review assesses the benefits, clinical applications, limitations, and future capabilities of WB-MRI in the context of other next-generation imaging modalities, as a qualitative and quantitative tool for the detection and characterization of skeletal and soft tissue MSK malignancies.