Low Dose Rate Irradiation Research Articles

Research on Calculation Method of Radiation Response Eigenvalue of a Single-Chip Active Pixel Sensor.

In this paper, we present a calculation method for the radiation response eigenvalue based on a monolithic active pixel sensor. By comparing the statistical eigenvalues of different regions of a pixel array in bright and dark environments, the linear relationship between the statistical eigenvalues obtained by different algorithms and the radiation dose rate was studied. Additionally, a dose rate characterization method based on the analysis of the eigenvalues of the MAPS response signal was proposed. The experimental results show that in the dark background environment, the eigenvalues had a good linear response in the region of any gray value in the range of 10–30. In the color images, due to the difference in the background gray values in adjacent color regions, the radiation response signal in dark regions was confused with the image information in bright regions, resulting in the loss of response signal and affecting the analysis results of the radiation response signal. For the low dose rate radiation field, as the radiation response signal was too weak and there was background dark noise, it was necessary to accumulate frame images to obtain a sufficient response signal. For the intense radiation field, the number of response events in a single image was very high, and only two consecutive frames of image data needed to be accumulated to meet the statistical requirements. The binarization method had a good characterization effect for the radiation at a low dose rate, and the binarization processing and the total gray value statistics of the response data at a high dose rate could better characterize the radiation dose rate. The calibration experiment results show that the binarization processing method can meet the requirements of using a MAPS for wide-range detection.

Abstract 2742: A biology-based, mathematical model to predict the response of recurrent glioblastoma to treatment with 186Re-labeled nanoliposomes

Abstract Introduction: 186Re-nanoliposomes (RNL) are a theranostic that emits a therapeutic payload of ionizing beta radiation, and a gamma photon to be measured with SPECT. The RNL is delivered via convection-enhanced delivery, resulting in a highly localized distribution around the glioma that produces up to a 30-fold increase in maximum tolerable dose. RNL provides a continuous source of low dose rate irradiation, until the particles are cleared biologically or decay. The goal of this study is to evaluate the accuracy of a patient calibrated reaction-diffusion equation for predicting the growth and response of recurrent glioblastoma multiforme (GBM) following treatment with RNL. Methods: Multi-parametric images were collected from patients (n=10) receiving RNL treatment, consisting of pre-treatment and follow-up MRIs (Day 0, 28*, 56, 112*) and SPECT/CTs acquired at the middle and end of infusion, and 24-, 112-, and 192-hours post-infusion. For each time point, tumor segmentations and cell count maps are computed using contrast enhanced and diffusion weighted MRI, respectively. The spatio-temporal response to RNL is modeled using a biology-informed reaction-diffusion model describing tumor cell proliferation, invasion, and radiation induced death. Key model parameters related to the RNL activity are populated through a quantification of the SPECT time course. The remaining model parameters related to diffusivity, proliferation, and death rate are calibrated via the Levenberg-Marquardt algorithm for each individual patient, and then used to forecast growth. Calibrations are performed in two different scenarios, first to all imaging time points to assess the model capabilities (Scenario 1), and then without the last acquired MRI, which is set aside to evaluate prediction accuracy (Scenario 2). Error will be assessed at the global (Dice similarity coefficient and percent error in total cell number) and local (concordance correlation coefficient or CCC) levels for both scenarios. *Patients are scanned on day 28 or day 112 at a minimum, potentially both (n=5) Results: Scenario 1 calibrations produced on average, Dice=0.92, CCC=0.69, and total cell percent error = 10.2%, validating usage of the current model formulation. Scenario 2 calibrations show high prediction success on a global scale, mean Dice=0.78, mean total cell percent error =23%, but resulted in poor local accuracy, mean CCC=0.21. Discussion & conclusion: The mathematical model and processing framework can predict the spatiotemporal evolution of recurrent GBM after treatment with RNL. Ongoing efforts include validating the methodology on a larger cohort and further model selection to improve predictive capabilities. Citation Format: Chase Christenson, Chengyue Wu, David A. Hormuth, Shiliang Huang, Andrew Brenner, Thomas E. Yankeelov. A biology-based, mathematical model to predict the response of recurrent glioblastoma to treatment with 186Re-labeled nanoliposomes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2742.

Application of Total Ionizing Dose Radiation Test Standards to SiC MOSFETs

The total ionizing dose (TID) test standards have been developed based on silicon devices to evaluate the TID response of MOS devices for space use. To estimate the applicability of the existing TID test standards to the wide-gap semiconductor silicon carbide (SiC) devices, 1200 V SiC n-channel MOSFETs from three manufacturers were irradiated with Cobalt-60 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> -rays at the high radiation dose rate of 50 rad(Si)/s and the low radiation dose rate of 0.01 rad(Si)/s, respectively. The threshold voltage of devices under test (DUT) shifted toward negative due to the radiation-induced positive oxide trapped charges. Room temperature (RT) anneal of maximum time of 2100 h and high temperature (HT) accelerated anneal of maximum temperature of 105 °C were performed, causing the threshold voltage shift to recover. The synergetic effects of temperature-gate-bias stress and TID on SiC MOSFETs were experimentally studied. In conclusion, the degradation of SiC MOSFETs irradiated at high dose rate is dominated by the positive trapped oxide charges, and the existing TID test standards are applicable to evaluate the SiC MOSFETs radiation hardness level, but the threshold voltages shift due to HT-gate-bias (HTGB) should be evaluated.

Ultrawide-range radiation detection based on dynamic identification and analysis of the response of a monolithic active pixel sensor.

In this paper, we present an ultrawide-range radiation detection method based on dynamic recognition and analysis of the response signal of a monolithic active pixel sensor (MAPS). Our analysis of the MAPS response mechanism determined that adaptive adjustment of the sensor's integral time is key to quantification of ionizing radiation in an ultrawide range. We also determined that different data processing methods are required for accurate quantification of high and low radiation dose rates. The results of experiments conducted after calibration demonstrate that our technique is capable of radiation detection across five orders of magnitude (ranging from milligrays per hour to hundreds of grays per hour), with errors of less than 5%. Chip-based nuclear radiation detection can be realized using our technique, enabling MAPS to be used as a supplement to traditional detectors in characterization of unknown and complex radiation environments.

Seed-Crystal-Induced Cold Sintering Toward Metal Halide Transparent Ceramic Scintillators.

Scintillators with high spatial resolution at a low radiation dose rate are desirable for X-ray medical imaging. To challenge the state-of-art technology, it is necessary to design large-area wafers with high light yield, oriented light transport, and reduced light scattering. Here, a seed-crystal-induced cold sintering is adopted and a <001>-textured TPP2 MnBr4 (TPP: tetraphenylphosphonium) transparent ceramic is fabricated with a large-area wafer of 5cm in diameter, exhibiting high optical transparency of above 68% over the 450-600nm range. The compelling scintillation performance of the TPP2 MnBr4 wafer includes a light yield of ≈78000± 2000 photons per MeV, a low detection limit 8.8 nanograys per second, about 625 times lower than the requirement of X-ray diagnostics (5500 nanograys per second), and an energy resolution of 17% for high-energy γ-rays (662keV). X-ray imaging demonstrates a high spatial resolution of 15.7 lp mm-1 . Moreover, the designed material exhibits good retention of the radioluminescence intensity and light yield. This work presents a paradigm for achieving light-guiding properties with high transparency and large-area fabrication by grain orientation engineering, and the transparent, textured metal halide ceramic scintillator is expected to provide a route for advancement in the X-ray imaging of tomorrow.

Radiation robustness of laser ceramics and single crystal for microchip laser remote analysis

Laser pulse energy and pulse build-up time were measured during gamma irradiation at a dose rate of 150 Gy h−1 to evaluate the radiation-induced effects and robustness on a laser remote inspection system using ceramics and single crystal microchip laser. Results showed a time-dependent decrease in pulse energy and an increase in pulse build-up time during irradiation. Both effects were larger for ceramics than for single crystals due to the amount of generated optical loss. The behaviors of pulse energy and build-up time with the increase in optical loss in the gain medium were simulated using rate equation calculations. The radiation effect on build-up time was larger than that on pulse energy for both specimens. Therefore, build-up time measurement is highly sensitive and effective for the evaluation of the radiation effect generated in laser medium, especially for radiation robust specimens or at low radiation dose rate.

Metabolomic Profiles of the Creeping Wood Sorrel Oxalis corniculata in Radioactively Contaminated Fields in Fukushima: Dose-Dependent Changes in Key Metabolites.

The biological impacts of the Fukushima nuclear accident, in 2011, on wildlife have been studied in many organisms, including the pale grass blue butterfly and its host plant, the creeping wood sorrel Oxalis corniculata. Here, we performed an LC–MS-based metabolomic analysis on leaves of this plant collected in 2018 from radioactively contaminated and control localities in Fukushima, Miyagi, and Niigata prefectures, Japan. Using 7967 peaks detected by LC–MS analysis, clustering analyses showed that nine Fukushima samples and one Miyagi sample were clustered together, irrespective of radiation dose, while two Fukushima (Iitate) and two Niigata samples were not in this cluster. However, 93 peaks were significantly different (FDR < 0.05) among the three dose-dependent groups based on background, low, and high radiation dose rates. Among them, seven upregulated and 15 downregulated peaks had single annotations, and their peak intensity values were positively and negatively correlated with ground radiation dose rates, respectively. Upregulated peaks were annotated as kudinoside D (saponin), andrachcinidine (alkaloid), pyridoxal phosphate (stress-related activated vitamin B6), and four microbe-related bioactive compounds, including antibiotics. Additionally, two peaks were singularly annotated and significantly upregulated (K1R1H1; peptide) or downregulated (DHAP(10:0); decanoyl dihydroxyacetone phosphate) most at the low dose rates. Therefore, this plant likely responded to radioactive pollution in Fukushima by upregulating and downregulating key metabolites. Furthermore, plant-associated endophytic microbes may also have responded to pollution, suggesting their contributions to the stress response of the plant.

Evaluation of risk due to chronic low dose ionizing radiation exposure on the birth prevalence of congenital heart diseases (CHD) among the newborns from high-level natural radiation areas of Kerala coast, India

BackgroundThe human population residing in monazite bearing Kerala coast are exposed to chronic low dose and low dose rate external gamma radiation due to Th232 deposits in its beach sand. The radiation level in this area varies from < 1.0 to 45.0 mGy/year. This area serves as an ideal source for conducting large-scale epidemiological studies for assessing risk of low dose and low dose rate radiation exposure on human population. The areas with a dose level of ≤1.50 mGy/year are considered as normal level natural radiation areas (NLNRAs) and areas with > 1.50 mGy/year, as high level natural radiation areas (HLNRAs). HLNRAs were further stratified into three dose groups of 1.51-3.0 mGy/year, 3.01-6.00 mGy/year and > 6.0 mGy/year. The present study evaluates the effects of chronic low dose radiation (LDR) exposure on the birth prevalence of Congenital Heart Diseases (CHD) among the live newborns monitored in hospital based prospective study from NLNRAs and HLNRAs of Kerala coast, India.MethodologyConsecutive newborns were monitored from two hospital units located in the study area for congenital malformations. Referred CHD cases among the newborns screened were confirmed by conducting investigations such as pulse oximetry, chest X-ray, electrocardiogram and echocardiogram etc.ResultsAmong the newborns screened, 289 CHDs were identified with a frequency of 1.49‰ among 193,634 livebirths, which constituted 6.03% of overall malformations and 16.29% of major malformations. Multiple logistic regression analysis suggested that the risk of CHD among the newborns of mothers from HLNRAs with a dose group of 1.51-3.0 mGy/year was significantly lower as compared to NLNRA (OR = 0.72, 95% CI: 0.57-0.92), whereas it was similar in HLNRA dose groups of 3.01-6.00 mGy/year (OR = 0.55, 95% CI: 0.31-1.00) and ≥ 6.0 mGy/year (OR = 0.96, 95% CI: 0.50-1.85). The frequency of CHDs did not show any radiation dose related increasing trend. However, a significant (P = 0.005) reduction was observed in the birth prevalence of CHDs among the newborns from HLNRA (1.28‰) as compared to NLNRA (1.79‰).ConclusionChronic LDR exposure did not show any increased risk on the birth prevalence of CHDs from high-level natural radiation areas of Kerala coast, India. No linear increasing trend was observed with respect to different background dose groups. The frequency of CHD was observed to be 1.49 per 1000 livebirths, which was similar to the frequency of severe CHD rate reported elsewhere in India and was much less than the reported frequency of 9 per thousand.

Relationship between micronucleus formation and oxidative stress in human vascular endothelial cells under low dose rate irradiation

Relationship between micronucleus formation and oxidative stress in human vascular endothelial cells under low dose rate irradiation

Ionizing radiation alters organoid forming potential and replenishment rate in a dose/dose-rate dependent manner.

Intestinal organoids are an in vitro cultured tissue model generated from intestinal stem cells, and they contain a mixture of epithelial cell types. We previously established an efficient ‘one cell/well’ sorting method, and defined organoid-forming potential (OFP) as a useful index to evaluate the stemness of individual cells. In this study, we assessed the response to radiation dose and dose-rate by measuring both OFP and the percentage of stem cells in the crypts. After high-dose-rate (HDR, 0.5 Gy/min) irradiation in vivo, the percentage of stem cells in the harvested crypt cells decreased, and the replenishment of cycling stem cells originating from dormant cells was enhanced, but OFP increased in cells irradiated with a total dose of >1 Gy. In contrast, at a total dose of 0.1 Gy the percentage of stem cells reduced slightly, but neither replenishment rate nor OFP changed. Furthermore, the response to 1 Gy of low-dose-rate (LDR) irradiation was similar to the response to 0.1 Gy HDR irradiation. These results suggest that 0.1 Gy HDR irradiation or 1 Gy LDR irradiation does not alter stemness. Additionally, the OFP increase in the colon in response to irradiation was smaller than that in the duodenum, similar to the percentage of stem cells. Understanding the differences in the response of stem cells between the colon and the duodenum to radiation is important to clarify the mechanisms underlying the development of radiation-associated intestinal cancers.

A Clinical Study on Pulsed Low Dose Rate Radiation Therapy for Recurrent Cancers

A Clinical Study on Pulsed Low Dose Rate Radiation Therapy for Recurrent Cancers

Characterization of hardening behavior of carbon steels at low temperature irradiations

• Embrittlement factors of carbon steels irradiated at low temperature were fine dislocation loops and solute clusters of Mn-Si-Cu atoms. • Carbon steels and their weld metals containing high concentrations of Cu, Mn and Si had relatively high radiation hardening due to promotion of solute atom clustering. • Low temperature irradiation resulted in higher radiation hardening due to the higher number density of dislocation loops, despite the lower number density of solute clusters. • Low dose rate irradiation (electron irradiation) resulted in greater radiation hardening due to the higher number density of solute clusters than high dose rate irradiation (ion irradiation) did. Overpacks used for geological disposal of high-level radioactive waste will be irradiated by neutrons and γ rays with very low dose rate for a long time. A possible way to predict effects of such radiations is that microstructure changes under the expected irradiation conditions are estimated by both experiments and analytical modeling and then the changes in hardness and fracture toughness from the microstructure changes are estimated. In the present study, carbon steels, which are one of the candidate materials for overpacks, model alloys and a weld of carbon steel were irradiated with either Fe ions or electrons at 90 or 290 °C, and then the microstructure and hardness were investigated to gain an understanding about embrittlement factors of carbon steels and effects of both material composition and irradiation conditions (temperature, dose rate) on radiation-induced changes in microstructure and hardness. Formations of fine dislocation loops and solute clusters containing Mn, Si and Cu atoms were confirmed by microstructure analysis using transmission electron microscopy and atom probe tomography. Hardness increase was well correlated with the evolution of dislocation loops and solute clusters, indicating that these defects are embrittlement factors of carbon steels. Higher radiation hardening was confirmed for the materials containing a high density of Mn, Si and Cu, and the irradiation conditions of low temperature and low dose rate.

Low Dose-Rate Irradiation of Gamma-Rays-Induced Cytotoxic and Genotoxic Alterations in Peripheral Erythrocytes of p53-Deficient Medaka (Oryzias latipes)

Morphological alterations and nuclear abnormalities in fish erythrocytes have been used in many studies as bioindicators of environmental mutagens including ionizing radiation. In this study, adult Japanese medaka (Oryzias latipes) were irradiated with gamma rays at a low dose rate (9.92 μGy/min) for 7 days, giving a total dose of 100 mGy; and morphological alterations, nuclear abnormalities, and apoptotic cell death induced in peripheral erythrocytes were investigated 8 h and 7 days after the end of the irradiation. A variety of abnormalities, such as tear-drop cell, crenated cell, acanthocyte, sickled cell, micronucleated cell, eccentric nucleus, notched nucleus, and schistocyte, were induced in the peripheral erythrocytes of the wild-type fish, and a less number of abnormalities and apoptotic cell death were induced in the p53-deficient fish. These results indicate that low dose-rate chronic irradiation of gamma rays can induce cytotoxic and genotoxic effects in the peripheral erythrocytes of medaka, and p53-deficient medaka are tolerant to the gamma-ray irradiation than the wild type on the surface.

Increased Frequency of Copy Number Variations Revealed by Array Comparative Genomic Hybridization in the Offspring of Male Mice Exposed to Low Dose-Rate Ionizing Radiation.

There is very little information on the transgenerational or genetic effects of low dose-rate ionizing radiation. We report the detection of the transgenerational effects of chronic low dose-rate irradiation in mice, at the molecular level in the whole genome, using array comparative genomic hybridization technology. We observed that the number of the mice with de novo copy number variations (specifically, deletions) was significantly increased in the offspring of C57BL/6J male mice exposed to 20 mGy/day gamma-rays for 400 days (total dose: 8000 mGy), as compared to non-irradiated controls. We did not detect any difference in the size of the de novo deletions between the irradiated and the non-irradiated groups. An analysis of the life span of the offspring suggested a possibility that de novo copy-number variations may be associated with shorter life spans.

Effect of gamma dose rate in the crosslinking of PVC composites used for radiation protection in radiology

Flexible PVC composites loaded with various levels of tantalum carbide (TaC) were gamma irradiated at two different dose rates and their effect on crosslinking level, thermal stability and mechanical properties evaluated. The shielding properties of composites against X-Rays at radiodiagnosis energies were also evaluated. Gel percentage results indicate a relatively stable crosslinking level after irradiation, only some reduction was observed for highly loaded composite treated at a low dose rate, although thermal stability observed by TGA was maintained. TaC particles were properly dispersed within the PVC material, as seen by SEM and toughness increased when both E' and E'' Moduli were enhanced after irradiation; even Tg, followed by Tanδ DMA curves, increased noticeably after treatment and for the higher TaC loaded composites, particularly when treated at low dose rate irradiation. Density measurements indicated lighter and manageable materials with respect to traditional shielding items. The shielding properties for composites, evaluated in a clinical X-Ray apparatus, in the 50–129 kV interval, show mass attenuation coefficients close to the ones reported for lead, even higher for 50% TaC loaded composite and a very competitive half-value layer (HVL) for all of them.

Biofluid Metabolomics of Mice Exposed to External Low-Dose Rate Radiation in a Novel Irradiation System, the Variable Dose-Rate External 137Cs Irradiator

An important component of ionizing radiation (IR) exposure after a radiological incident may include low-dose rate (LDR) exposures either externally or internally, such as from 137Cs deposition. In this study, a novel irradiation system, VAriable Dose-rate External 137Cs irradiatoR (VADER), was used to expose male and female mice to a variable LDR irradiation over a 30 d time span to simulate fall-out-type exposures in addition to biofluid collection from a reference dose rate (0.8 Gy/min). Radiation markers were identified by untargeted metabolomics and random forests. Mice exposed to LDR exposures were successfully identified from control groups based on their urine and serum metabolite profiles. In addition to metabolites commonly perturbed after IR exposure, we identified and validated a novel metabolite (hexosamine-valine-isoleucine-OH) that increased up to 150-fold after LDR and 80-fold after conventional exposures in urine. A multiplex panel consisting of hexosamine-valine-isoleucine-OH with other urinary metabolites (N6,N6,N6-trimethyllysine, carnitine, 1-methylnicotinamide, and α-ketoglutaric acid) achieved robust classification performance using receiver operating characteristic curve analysis, irrespective of the dose rate or sex. These results show that in terms of biodosimetry, dysregulated energy metabolism is associated with IR exposure for both LDR and conventional IR exposures. These mass spectrometry data have been deposited to the NIH data repository via Metabolomics Workbench with study IDs ST001790, ST001791, ST001792, ST001793, and ST001806.

Total Ionizing Dose Effect and Failure Mechanism of Digital Signal Processor

Ionizing radiation effect and failure mechanism of Digital signal processor (DSP) is studied through test-board and automatic test equipment to find the relationship between system function failure and parameter degradation. Static bias is more sensitive than dynamic bias when DSP is tested on-line during radiation. Core current, high-Z leakage current and timing parameter are sensitive to ionizing radiation. No enhanced low-dose-rate sensitivity is found by comparing experiment results under high and low dose rate radiation. External memory interface and Timer are deduced to be the sensitive module by step radiation and analysis basing full parameter test in Verigy 93000. The timing parameter degradation have a strong correlation to these module functions. And the degeneration mechanism is analysed on inverter through Hspice simulation which indicate the leakage circuit caused by radiation can lead a delay to the digital signal propagating. The parasitical capacitance among long connections make it worse to the data transmission around DSP, field programmable gate array and memory. Then an early function failure occurs in test board than Verigy 93000. This work provide support to systematic radiation hardness design and hardness assurance/lot acceptance testing in space applications.

Pulsed low-dose rate radiotherapy has an improved therapeutic effect on abdominal and pelvic malignancies.

Until now, there has been a lack of standard and effective treatments for patients with recurrent malignant tumors or abdominal and pelvic malignancies with extensive invasion (Morris, 2000). Generally, these patients face problems such as inability to undergo surgery or chemotherapy resistance (Combs et al., 2016). Re-radiotherapy has achieved a prominent place in the treatment of patients who have received radiotherapy previously and developed in-field recurrences (Straube et al., 2018). However, re-radiotherapy is very complicated, requiring comprehensive consideration of appropriate radiation dose, interval from first radiotherapy, boundary of the radiotherapy target area, and damage to surrounding normal tissues (Straube et al., 2019). In other words, it is necessary to focus on the protection of surrounding normal tissues while maximizing the efficacy of re-radiotherapy in such patients.

Perturbed transcriptional profiles after chronic low dose rate radiation in mice.

Adverse health outcomes of ionizing radiation given chronically at low dose rates are highly debated, a controversy also relevant for other stressors. Increased knowledge is needed for a more comprehensive understanding of the damaging potential of ionizing radiation from all dose rates and doses. There is a lack of relevant low dose rate data that is partly ascribed to the rarity of exposure facilities allowing chronic low dose rate exposures. Using the FIGARO facility, we assessed early (one day post-radiation) and late (recovery time of 100-200 days) hepatic genome-wide transcriptional profiles in male mice of two strains (CBA/CaOlaHsd and C57BL/6NHsd) exposed chronically to a low dose rate (2.5 mGy/h; 1200h, LDR), a mid-dose rate (10 mGy/h; 300h, MDR) and acutely to a high dose rate (100 mGy/h; 30h, HDR) of gamma irradiation, given to an equivalent total dose of 3 Gy. Dose-rate and strain-specific transcriptional responses were identified. Differently modulated transcriptional responses across all dose rate exposure groups were evident by the representation of functional biological pathways. Evidence of changed epigenetic regulation (global DNA methylation) was not detected. A period of recovery markedly reduced the number of differentially expressed genes. Using enrichment analysis to identify the functional significance of the modulated genes, perturbed signaling pathways associated with both cancer and non-cancer effects were observed, such as lipid metabolism and inflammation. These pathways were seen after chronic low dose rate and were not restricted to the acute high dose rate exposure. The transcriptional response induced by chronic low dose rate ionizing radiation suggests contribution to conditions such as cardiovascular diseases. We contribute with novel genome wide transcriptional data highlighting dose-rate-specific radiation responses and emphasize the importance of considering both dose rate, duration of exposure, and variability in susceptibility when assessing risks from ionizing radiation.

Comparison of 186Re to 662 keV photon radiation concerning biological radiation effect on the human B-cell line BV-173

Zellen der humanen Leukämie-Zelllinie BV-173 wurden mit 662keV-Photonenstrahlung respektive 186Re bestrahlt. In einem Inkubationszeitraum von 7 Tagen wurden Zahl und Vitalität der Zellen täglich bestimmt und als Dosiseffektkurven basierend auf der Vitalität dargestellt. Hierfür wurde der Zeitpunkt mit minimalem Überleben verwendet (72h 186Re und 24h Photonenstrahlung). Beide Strahlenarten zeigen am Auswertezeitpunkt (72h nach Versuchsbeginn für 186Re und 24h nach Versuchsbeginn für Photonenstrahlung) eine Überlebenskurve mit biexponentiellem Verlauf. Für Photonenstrahlung ist dies erklärbar durch eine Hypersensitivität im niedrigen Dosisbereich bis 1Gy, für die sich eine D0 von 3,3Gy ergibt, für Dosen über 1,0Gy liegt die D0 bei 10Gy. Für die 186Re-Inkubation ergibt sich eine D0 von 11,1Gy bei niedrigen Dosen verursacht durch die Reparatur subletaler Schäden, durch welche die biologische Wirkung abgeschwächt wird. Ab einer akkumulierten Dosis von etwa 1,6Gy zeichnet sich für 186Re ein wesentlich steilerer Kurvenverlauf mit einer D0 von 4,0Gy ab, der eine in diesem Bereich 2,5-fach stärkere biologische Wirkung als akute Photonenstrahlung wiedergibt (D0 4Gy für 186Re bzw. 10Gy für Photonen). Strahlung niedriger Dosisleistung zeigt eine geringere biologische Wirkung als eine akute Bestrahlung. Es existiert aber ein Grenzwert der akkumulierten Dosis, ab dem die biologische Wirkung von β-Strahlung die der Photonenstrahlung sogar übertrifft.