Linear Energy Transfer Radiation Research Articles

High LET-Like Radiation Tracks at the Distal Side of Accelerated Proton Bragg Peak.

Proton therapy is a type of hadron radiotherapy used for treating solid tumors. Unlike heavy charged elements, proton radiation is considered to be low LET (Linear Energy Transfer) radiation, like X-rays. However, the clinical SOBP (Spread Out Bragg Peak) proton radiation is considered to be higher in relative biological effectiveness (RBE) than both X-ray and their own entrance region. The RBE is estimated to be 1.1–1.2, which can be attributed to the higher LET at the SOBP region than at the entrance region. In order to clarify the nature of higher LET near the Bragg peak of proton radiation and its potential cytotoxic effects, we utilized a horizontal irradiation system with CHO cells. Additionally, we examined DNA repair mutants, analyzed cytotoxicity with colony formation, and assessed DNA damage and its repair with γ-H2AX foci assay in a high-resolution microscopic scale analysis along with the Bragg peak. Besides confirming that the most cytotoxic effects occurred at the Bragg peak, extended cytotoxicity was observed a few millimeters after the Bragg peak. γ-H2AX foci numbers reached a maximum at the Bragg peak and reduced dramatically after the Bragg peak. However, in the post-Bragg peak region, particle track-like structures were sporadically observed. This region contains foci that are more difficult to repair. The peak and post-Bragg peak regions contain rare high LET-like radiation tracks and can cause cellular lethality. This may have caused unwanted side effects and complexities of outputs for the proton therapy treatment.

Longitudinal metabolic alterations in plasma of rats exposed to low doses of high linear energy transfer radiation

Astronauts embarking on deep space missions are at high risk of long-term exposure to low doses of high linear energy transfer (LET) radiation, which can contribute to the development of cancer and multiple degenerative diseases. However, long term effects of exposure to low doses of high LET radiation in plasma metabolite profiles have not been elucidated. We utilized an untargeted metabolomics and lipidomics approach to analyze plasma obtained from adult male Long Evans rats to determine the longitudinal effects of low-dose proton and low-dose oxygen ion whole-body irradiation on metabolic pathways. Our findings reveal that radiation exposure induced modest changes in the metabolic profiles in plasma, 7 months after exposure. Furthermore, we identified some common metabolite dysregulations between protons and oxygen ions, which may indicate a similar mechanism of action for both radiation types.

Dual-storage phosphor proton therapy dosimetry: Simultaneous quantification of dose and linear energy transfer.

To investigate the feasibility of using the high Zeff storage phosphor material BaFBrI:Eu2+ in conjunction with the low Zeff storage phosphor material KCl:Eu2+ for simultaneous proton dose and linear energy transfer (LET) measurements by (a) measuring the fundamental optical and dosimetric properties of BaFBrI:Eu2+ , (b) evaluating its compatibility in being readout simultaneously with KCl:Eu2+ dosimeters, and (c) modeling and validating its LET dependence under elevated proton LET irradiation. A commercial BaFBrI:Eu2+ storage phosphor detector (Model ST-VI, Fujifilm) was characterized with energy dispersive x-ray spectroscopy (EDS) analysis to obtain its elemental composition. The dosimeters were irradiated using both a Mevion S250 proton therapy unit (at the center of a spread-out Bragg peak, SOBP) and a Varian Clinac iX linear accelerator with the latter being a low LET irradiation. The photostimulated luminescence (PSL) emission spectra, excitation spectra, and luminescent lifetimes of the detector were measured after proton and photon irradiations. Dosimetric properties including dose linearity, dose rate dependence, radiation hardness, temporal, and readout stabilities were studied using a laboratory optical reader after proton irradiations. In addition, its proton energy dependence was analytically modeled and experimentally validated by irradiating the detectors at various depths within the SOBP (Range: 15.0g/cm2 , Modulation: 10.0g/cm2 ). The active detector composition for the high Zeff storage phosphor detector was found to be BaFBr0.85 I0.15 :Eu2+ . The BaFBr0.85 I0.15 :Eu2+ material's excitation and emission spectra were in agreement under proton and photon irradiations, with peaks of 586±1nm and 400±1nm, respectively, with a full width at half maximum (FWHM) of 119±3nm and 30±2nm, respectively. As dosimeter response under photon irradiation is generally believed to be free from LET effect, these results suggest LET independence of charge storage center types resulted from ionizing radiations. There is sufficient spectral overlaps with KCl:Eu2+ dosimeters allowing both dosimeters to be readout under equivalent readout conditions, that is, 594nm stimulation and 420nm detection wavelengths. Its PSL characteristic lifetime was found to be less than 5 microseconds which would make it suitable for fast 2D readout post irradiation. Its 420nm emission band intensity was found to be linear up to 10Gy absolute proton dose under the same irradiation conditions, dose rate independent, stable in time and under multiple readouts, and with high radiation hardness under cumulative proton dose histories up to 200Gy as tested in this study. BaFBr0.85 I0.15 :Eu2+ showed significant proton energy-dependent dose under-response in regions of high LET which could be modeled by stopping power ratio calculations with an accuracy of 3% in low LET regions and a distance-to-agreement (DTA) of 1mm in high LET regions (>5keV/μm). We have proven the feasibility of dual-storage phosphor proton dosimetry for simultaneous proton dose and LET measurements. BaFBr0.85 I0.15 :Eu2+ has shown equally excellent dosimetry performance as its low Zeff complement KCl:Eu2+ with distinctive LET dependence merely as a result of its higher Zeff . These promising results pave the way for future studies involving simultaneous proton dose and LET measurements using this novel approach.

Fast neutron energy based modelling of biological effectiveness with implications for proton and ion beams

A practical neutron energy dependent RBE model has been developed, based on the relationship between a mono-energetic neutron energy and its likely recoil proton energy. Essentially, the linear energy transfer (LET) values of the most appropriate recoil proton energies are then used to modify the linear quadratic model radiosensitivities (α and β) from their reference LET radiation values to provide the RBE estimates. Experimental neutron studies published by Hall (including some mono-energetic beams ranging from 0.2 to 15 MeV), Broerse, Berry, and data from the Clatterbridge and Detroit clinical neutron beams, which all contain some data from a spectrum of neutron energies, are used to derive single effective neutron energies (NEeff) for each spectral beam. These energies yield a recoil proton spectrum, but with an effective mean proton energy (being around 50% of NEeff). The fractional increase in LET is given by the recoil proton LET divided by the proton (LETU) value which provides the highest RBE. This ratio is then used to determine the change in the linear-quadratic model α and β parameters, from those of the reference radiation, to estimate the RBE. The predicted proton recoil RBE is then reasonably close to the experimental neutron RBE values found when taking into account the variation inherent in biological experiments. The work has some important consequences. The data of Hall et al (1975 Radiat. Res. 64 245–55) shows that the highest RBE values are found with neutron energies around 0.3–0.4 MeV, but this energy cannot possibly generate recoil proton energies which are higher, as necessary for a 0.68 MeV proton with a 30.5 keV μm−1 LETU (the LET value which provides the maximum obtainable RBE for a specified ion). For 0.4 MeV neutrons with proton recoil energies of around 0.2 MeV, the latter have a LET of around 62.88 keV μm−1. This could have an impact on proton beam RBE modelling. However, this is compensated by finding that the maximum radiosensitivity for mono-energetic neutrons was around 1.7 times larger than previously suggested from experimental ion beam studies, probably due to the necessary spreading out of Bragg peaks for ion beam experimental purposes, sampling errors and particle range considerations. This semi-empirical model can be used with minimal computer support and could have applications in ionic beams and in radioprotection.

Harm of high LET radiation to the lens of the human eye

The biological effects of ionising radiation vary according to its linear energy transfer (LET) density, with higher LET radiation having stronger biological effects than lower LET radiation at the same absorbed dose. Though we have done more research in the area of radiation effects on the ocular lens, we know little about the effects of high LET on the ocular lens. This article briefly describes the historical changes in the dose limits of the human ocular lens, investigates the epidemiology of high LET radiation eye lens, summarizes various biological experiments of high LET particles, and briefly analyzes the reasons for the high prevalence of cataracts in the plateau. It also discusses the factors that need to be considered in the future research on high LET, aiming to provide valuable information for the future research of high LET eye lens in China. 摘要： 眼晶状体是人体对辐射最敏感的组织之一, 电离辐射的生物效应因其传能线密度 (linear energy transfer, LET) 的不同而不同, 同等吸收剂量条件下, 高 LET 辐射生物效应比低 LET 辐射更强, 尽管目前辐射对眼晶状体的影响这一 领域己经有了较多研宄, 但对于高 LET 对眼晶状体的影响知之甚少。本文简述人眼晶状体剂量限值的历史变化情况, 综述各种高 LET 粒子的生物学实验, 调查高 LET 辐射眼晶状体的流行病学, 简要分析高原白内障高患病率的原因, 并 初步讨论未来研宄高 LET 需要考虑的因素, 旨在为国内今后开展高 LET 辐射对人眼晶状体的研宄提供有价值的信息。

Does the combination of hyperthermia with low LET (linear energy transfer) radiation induce anti-tumor effects equivalent to those seen with high LET radiation alone?

Introduction The combination of hyperthermia with low LET (linear energy transfer) radiation may have similar anti-tumor effects as high LET radiation alone. This pre-clinical study determined the optimal heating temperature and time interval between radiation and heat to achieve this equivalent effect. Methods C3H mammary carcinomas (200 mm3 in size) growing in the right rear foot of CDF1 mice was used in all experiments. Tumors were locally irradiated with graded doses of either 240 kV ortho- or 6 MV mega-voltage X-rays to produce full dose-response curves. Heating (41.0–43.5 °C; 60 min) was achieved by immersing the tumor bearing foot in a water-bath applied at the same time, or up to 4-hours after, irradiating. The endpoint was the percentage of mice showing local tumor control at 90 days, with enhancements calculated from the ratios of the radiation doses causing 50% tumor control (± 95% confidence intervals). Results Previous published results in this tumor model reported that carbon ions were 1.3–1.7 times more effective than low LET radiation at inducing tumor control. Similar enhancements occurred with a temperature of only 41.0 °C with a simultaneous heat and radiation treatment. However, higher temperatures were needed with the introduction of any interval; at 42.5 °C, the enhancement was 2.5 with a simultaneous treatment, decreasing to a value within the carbon ion range with a 4-hour interval. Conclusions Combining hyperthermia with low LET radiation can be as effective as high LET at inducing tumor control, but the temperature needed depended on the time interval between the two modalities.

Fluorescence anisotropy study of radiation-induced DNA damage clustering based on FRET.

A clustered DNA damage site (cluster), in which two or more lesions exist within a few helical turns, is believed to be a key factor determining the fate of a living cell exposed to a DNA damaging agent such as ionizing radiation. However, the structural details of a cluster such as the number of included lesions and their proximity are unknown. Herein, we develop a method to characterize a cluster by fluorescence anisotropy measurements based on Förster resonance energy transfer (homo-FRET). Plasmid DNA (pUC19) was irradiated with 2.0 and 0.52MeV/u 4He2+, or 0.37MeV/u 12C5+ ion beams (linear energy transfer: ~ 70, ~ 150, ~ 760keV/μm, respectively) and 60Co γ-rays as a standard (~ 0.2keV/μm) in the solid state. The irradiated DNA was labeled with an aminooxyl fluorophore (Alexa Fluor 488) to the aldehyde/ketone moieties such as apurinic/apyrimidinic sites. Homo-FRET analyses provided the apparent base separation values between lesions in a cluster produced by each ion beam track as 21.1, 19.4, and 18.7 base pairs. The production frequency of a cluster increases with increasing linear energy transfer of radiation. Our results demonstrate that homo-FRET analysis has the potential to discover the qualitative and the quantitative differences of the clusters produced not only by a variety of ionizing radiation but also by other DNA damaging agents.

Radiosensitization of NSCLC cells to X-rays and carbon ions by the CHK1/CHK2 inhibitor AZD7762, Honokiol and Tunicamycin.

Although radiotherapy, especially carbon-ion radiotherapy, is an effective treatmentmodality against non-small-cell lung cancer (NSCLC), studies using radiation combined with sensitizer for improving the efficacy of radiotherapy are still needed. In this work, we aimed to investigate in NSCLC A549 and H1299 cell lines the effects of different linear energy transfer (LET) radiations combined with diverse sensitizing compounds. Cells pretreated with the CHK1/CHK2 inhibitor AZD7762, Honokiol or Tunicamycin were irradiated with low-LET X-rays and high-LET carbon ions. Cell survival was assessed using the clonogenic cell survival assay. Cell cycle distribution and apoptosis were measured with flow cytometry, and DNA double strand break (DSB) and repair were detected using γ-H2AX immunofluorescence staining. Our results revealed that AZD7762, Honokiol and Tunicamycin demonstrated low cytotoxicity to NSCLC cells and a pronounced radiosensitizing effect on NSCLC cells exposed to carbon ions than X-rays. Unrepaired DNA DSB damages, the abrogation of G2/M arrest induced by irradiation, and finally apoptotic cell death were the main causes of the radiosensitizing effect. Thus, our data suggest that high-LET carbon ion combined with these compounds may be a potentially effective therapeutic strategy for locally advanced NSCLC.

The Impacts of Different Types of Radiation on the CRT and PDL1 Expression in Tumor Cells Under Normoxia and Hypoxia.

IntroductionHypoxia is a hallmark of cancer that may contribute to an immunosuppressive microenvironment and promote radioresistance. High linear energy transfer (LET) radiation is considered to be able to overcome the negative effects of hypoxia. However, the anti-tumorigenic effects induced by low or high LET radiation have not been fully elucidated. This study aimed to compare the effects of different types of radiation on the immune response, particularly the impact on calreticulin (CRT), and programmed cell death ligand 1 (PDL1) expression.MethodsFour human tumor cell lines were investigated in this study. Cells in normoxic and hypoxic groups were irradiated with 4Gy (physical dose) photon, proton, and carbon-ion radiation, respectively. The expression of CRT and PDL1 was detected 48 h after irradiation, and the median fluorescence intensities (MFIs) were compared by flow cytometry. Meanwhile, the radiosensitivity of tumor cells in each group was also compared by colony formation assays and flow cytometry.ResultsAll types of radiation could significantly inhibit the colony formation of tumor cells under normoxia. However, the efficacy of photon and proton radiation was impaired under hypoxia. Carbon-ion radiation could still inhibit colony formation. The percentage of viable cells after irradiation was higher under hypoxia compared with those under normoxia. The CRT expression under normoxia was significantly increased after radiation. Carbon-ion radiation enhanced CRT expression compared to photon and proton radiation. Conversely, under hypoxia, the CRT expression level was significantly upregulated at baseline (0Gy). Radiation could not increase the expression further. PDL1 expression was also significantly increased by radiation under normoxia in all cell lines except the Ln18 cell line. Carbon-ion radiation induced the most significant increase. Under hypoxia, the PDL1 expression level was also upregulated at baseline and radiation could not increase expression further.ConclusionTumor cells were resistant to photon and proton but sensitive to carbon-ion radiation under hypoxia. Carbon-ion radiation could induce the highest CRT and PDL1 expression under normoxia. However, under hypoxia, radiation could not further enhance the high baseline expression of CRT and PDL1.

Heavy ion radiation-induced DNA damage mediates apoptosis via the Rpl27a-Rpl5-MDM2-p53/E2F1 signaling pathway in mouse spermatogonia.

The risk of exposure to ionizing radiation (IR) environments has increased with the development of nuclear technology. IR exposure induces excessive apoptosis of the spermatogonia, which leads to male infertility. Spermatogonia apoptosis may be involved in ribosomal stress triggered by DNA damage following exposure to IR because ribosomal proteins (RPs) directly interact with mouse double minute 2 homolog (MDM2) to induce apoptosis. This study aimed to use comparative proteomics and transcriptomics approach to screen the differential RPs and ribosomal mRNAs in mouse testes following high linear energy transfer (LET) carbon ion radiation (CIR). The expression of ribosomal large subunit protein 27a (Rpl27a) decreased at both protein and mRNA levels in the spermatogonia in vivo. After 6h of CIR, the immunofluorescence signal of 8-oxo-dG and phosphorylated ataxia-telangiectasia-mutated protein (ATM)/histone H2Ax increased, but that of Rpl27a decreased in the spermatogonia of p53 wild-type and knockout mouse testes. Moreover, the nucleolin was scattered throughout the nucleoplasm after CIR. These results suggested that CIR-induced DNA damage might trigger ribosomal stress, and the reduction in the expression of Rpl27a was associated with DNA damage in the spermatogonia. Similarly, in vitro, the immunofluorescence signal of 8-oxo-dG increased in the GC-1cells after CIR. Moreover, the expression of Rpl27a was regulated by DNA damage because the co-transfection of ATM and Rpl27a or inhibition of ATM-treated CIR could restore the expression of Rpl27a. Furthermore, the reduction in the expression of Rpl27a led to weakened binding of E2F transcription factor 1 (E2F1) and p53 to MDM2, causing p53 activation and E2F1 degradation in p53 wild-type and knockdown GC-1cells. This study proposed that heavy ion radiation-induced DNA damage mediated spermatogonia apoptosis via the Rpl27a-Rpl5-MDM2-p53/E2F1 signaling pathway. The results provided the underlying molecular mechanisms of spermatogonia apoptosis following exposure to high LET radiation.

The Unfolded Protein Response: Neutron-Induced Therapy Autophagy as a Promising Treatment Option for Osteosarcoma.

Radiotherapy using high linear energy transfer (LET) radiation results in effectively killing tumor cells while minimizing dose (biological effective) to normal tissues to block toxicity. It is well known that high LET radiation leads to lower cell survival per absorbed dose than low LET radiation. High-linear energy transfer (LET) neutron treatment induces autophagy in tumor cells, but its precise mechanisms in osteosarcoma are unknown. Here, we investigated this mechanism and the underlying signaling pathways. Autophagy induction was examined in gamma-ray-treated KHOS/NP and MG63 osteosarcoma cells along with exposure to high-LET neutrons. The relationship between radiosensitivity and autophagy was assessed by plotting the cell surviving fractions against autophagy levels. Neutron treatment increased autophagy rates in irradiated KHOS/NP and MG63 cells; neutrons with high-LETs showed more effective inhibition than those with lower LET gamma-rays. To determine whether the unfolded protein response and Akt-mTOR pathways triggered autophagy, phosphorylated eIF2α and JNK levels, and phospho-Akt, phosphor-mTOR, and phospho-p70S6 levels were, respectively, investigated. High-LET neutron exposure inhibited Akt phosphorylation and increased Beclin 1 expression during the unfolded protein response, thereby enhancing autophagy. The therapeutic efficacy of high-LET neutron radiation was also assessed in vivo using an orthotopic mouse model. Neutron-irradiated mice showed reduced tumor growth without toxicity relative to gamma-ray-treated mice. The effect of high-LET neutron exposure on the expression of signaling proteins LC3, p-elF2a, and p-JNK was investigated by immunohistochemistry. Tumors in high-LET-neutron radiation-treated mice showed higher apoptosis rates, and neutron exposure significantly elevated LC3 expression, and increased p-elF2a and p-JNK expression levels. Overall, these results demonstrate that autophagy is important in radiosensitivity, cell survival, and cellular resistance against high-LET neutron radiation. This correlation between cellular radiosensitivity and autophagy may be used to predict radiosensitivity in osteosarcoma.

Clustered DNA Double-Strand Breaks: Biological Effects and Relevance to Cancer Radiotherapy.

Cells manage to survive, thrive, and divide with high accuracy despite the constant threat of DNA damage. Cells have evolved with several systems that efficiently repair spontaneous, isolated DNA lesions with a high degree of accuracy. Ionizing radiation and a few radiomimetic chemicals can produce clustered DNA damage comprising complex arrangements of single-strand damage and DNA double-strand breaks (DSBs). There is substantial evidence that clustered DNA damage is more mutagenic and cytotoxic than isolated damage. Radiation-induced clustered DNA damage has proven difficult to study because the spectrum of induced lesions is very complex, and lesions are randomly distributed throughout the genome. Nonetheless, it is fairly well-established that radiation-induced clustered DNA damage, including non-DSB and DSB clustered lesions, are poorly repaired or fail to repair, accounting for the greater mutagenic and cytotoxic effects of clustered lesions compared to isolated lesions. High linear energy transfer (LET) charged particle radiation is more cytotoxic per unit dose than low LET radiation because high LET radiation produces more clustered DNA damage. Studies with I-SceI nuclease demonstrate that nuclease-induced DSB clusters are also cytotoxic, indicating that this cytotoxicity is independent of radiogenic lesions, including single-strand lesions and chemically “dirty” DSB ends. The poor repair of clustered DSBs at least in part reflects inhibition of canonical NHEJ by short DNA fragments. This shifts repair toward HR and perhaps alternative NHEJ, and can result in chromothripsis-mediated genome instability or cell death. These principals are important for cancer treatment by low and high LET radiation.

Impact of Target Oxygenation on the Chemical Track Evolution of Ion and Electron Radiation.

The radiosensitivity of biological systems is strongly affected by the system oxygenation. On the nanoscopic scale and molecular level, this effect is considered to be strongly related to the indirect damage of radiation. Even though particle track radiolysis has been the object of several studies, still little is known about the nanoscopic impact of target oxygenation on the radical yields. Here we present an extension of the chemical module of the Monte Carlo particle track structure code TRAX, taking into account the presence of dissolved molecular oxygen in the target material. The impact of the target oxygenation level on the chemical track evolution and the yields of all the relevant chemical species are studied in water under different irradiation conditions: different linear energy transfer (LET) values, different oxygenation levels, and different particle types. Especially for low LET radiation, a large production of two highly toxic species ( and ), which is not produced in anoxic conditions, is predicted and quantified in oxygenated solutions. The remarkable correlation between the and production yield and the oxygen enhancement ratio observed in biological systems suggests a direct or indirect involvement of and in the oxygen sensitization effect. The results are in agreement with available experimental data and previous computational approaches. An analysis of the oxygen depletion rate in different radiation conditions is also reported. The radiosensitivity of biological systems is strongly affected by the system oxygenation. On the nanoscopic scale and molecular level, this effect is considered to be strongly related to the indirect damage of radiation. Even though particle track radiolysis has been the object of several studies, still little is known about the nanoscopic impact of target oxygenation on the radical yields. Here we present an extension of the chemical module of the Monte Carlo particle track structure code TRAX, taking into account the presence of dissolved molecular oxygen in the target material. The impact of the target oxygenation level on the chemical track evolution and the yields of all the relevant chemical species are studied in water under different irradiation conditions: different linear energy transfer (LET) values, different oxygenation levels, and different particle types. Especially for low LET radiation, a large production of two highly toxic species ( and ), which is not produced in anoxic conditions, is predicted and quantified in oxygenated solutions. The remarkable correlation between the and production yield and the oxygen enhancement ratio observed in biological systems suggests a direct or indirect involvement of and in the oxygen sensitization effect. The results are in agreement with available experimental data and previous computational approaches. An analysis of the oxygen depletion rate in different radiation conditions is also reported.

MEAN VALUE OF LET FOR ONCOGENIC EFFECTS OF RADON AND ITS PROGENY

The topic of the article is to define the average value of linear energy transfer (LET) for carcinogenic effects of radon progeny. The microdosimetric model of boundary specific energy is used. It follows that the effect at high LET should decrease approximately with the third power of LET. This is verified by the analysis of the relationship between radiation effects ratio and LET in published experiments with oncogenic transformation of mammalian cells irradiated with the monoenergetic alpha particles. If these cells are exposed with the radon irradiator, our analysis leads us to conclude that the oncogenic effect of radon progeny is comparable to that of alpha particles with a LET of 75keV/μm. It is about a quarter lower than the LET value, where the effect of the monoenergetic alpha particles reaches its maximum level. Some implications for lung cancer due to radon inhalation may also be carefully examined.

Influence of dose-averaged linear energy transfer on tumour control after carbon-ion radiation therapy for pancreatic cancer

Background and purposeHigh linear energy transfer (LET) radiation carbon-ion radiotherapy (C-ion RT) is one of the most promising modalities for treating unresectable primary pancreatic cancers. However, how LET contributes to a therapeutic effect is not clear. To assess whether there is an enhanced effect of high LET radiation on tumour control, we aimed to determine the impact of dose-averaged LET on local control (LC) of primary pancreatic tumours. Materials and methodsA retrospective analysis of 18 patients with primary pancreatic carcinomas treated with definitive C-ion RT with concurrent chemotherapy in 2013 was conducted. The dose of irradiation was 55.2 Gy (RBE). The relationship between dose-averaged LET and LC of primary tumours was evaluated. ResultsAll patients had histologically confirmed adenocarcinoma. The median follow-up duration was 22 months. The actuarial LC and overall survival (OS) at 18 months were 62.5% and 70.1%, respectively. There were no cases of grade ≥3 late toxicities observed. Local recurrences developed in four patients (22%), all of which were infield central recurrences. Although there were no significant differences in gross tumour volume (GTV) dose coverage, patients with higher minimum dose-averaged LET (LETmin) values within the GTV had better LC (dose-averaged LETmin ≥44 keV/microm; 18-months LC 100.0% vs 34.3%; p = 0.0366). ConclusionDose-averaged LETmin within the GTV was significantly associated with LC of primary pancreatic cancers. Our data suggest that outcomes for patients with unresectable primary pancreatic cancers receiving C-ion RT can be improved by modulating the dose-averaged LET within the GTV.

Design and dosimetry of a facility to study health effects following exposures to fission neutrons at low dose rates for long durations

Purpose During extended missions into deep space, astronauts will be exposed to a complex radiation field that includes high linear energy transfer (LET) radiation from high energy, heavy ions (HZE particles) at low dose rates of about 0.5 mGy/d for long durations. About 20% of the dose is delivered by ions with LET greater than 10 keV/µm. There are sparse empirical data in any species for carcinogenic effects from whole-body exposures to external sources of mixed or high LET radiation at this level of dose rates. For the induction of solid tumors, acute exposures to HZE ions have been shown to be substantially more effective per unit dose than low LET exposures associated with photons. To determine the health effects of high LET radiation at space-relevant dose rates on experimental animals, we developed a vivarium in which rodents could be irradiated with Californium (252Cf) neutrons for protracted periods of time. Materials and methods The neutron source is a panoramic irradiator containing 252Cf located in a concrete shielded vault with a footprint of 53 m2. The vault can accommodate sufficient caging to simultaneously irradiate 900 mice and 60 rats for durations up to 400 d at a dose rate of 1 mGy/d and is approved for extended animal husbandry. Results The mixed field fluence is a combination of neutrons and photons emitted directly from the source and scattered particles from the concrete walls and floor. Mixed field dosimetry was performed using a miniature GM counter and CaF2:Dy thermoluminescent dosimeters (TLD) for photons and tissue-equivalent proportional counters (TEPC) for neutrons. TEPC data provided macroscopic dose rates as well as measurements of radiation quality based on lineal energy, y, and LET. The instantaneous dose rate from the source decreases with a half-life of 2.6 years. The exposure time is adjusted weekly to yield a total dose 1 mGy/d. The photon contribution is 20% of the total dose. The uncertainty in the delivered dose is estimated to be ±20% taking into account spatial variations in the room and random position of mice in each cage. The dose averaged LET for the charged particle recoil nuclei is 68 keV/µ. Conclusions We have developed a facility to perform high LET studies in mice and rats at space relevant dose rates and career-relevant doses using neutrons emitted from the spontaneous fission of 252Cf.

Presence of Stromal Cells Enhances Epithelial-to-Mesenchymal Transition (EMT) Induction in Lung Bronchial Epithelium after Protracted Exposure to Oxidative Stress of Gamma Radiation.

The aim of the study was to investigate the role of a microenvironment in the induction of epithelial-to-mesenchymal transition (EMT) as a sign of early stages of carcinogenesis in human lung epithelial cell lines after protracted low-dose rate γ-radiation exposures. BEAS-2B and HBEC-3KT lung cell lines were irradiated with low-dose rate γ-rays (137Cs, 1.4 or 14 mGy/h) to 0.1 or 1 Gy with or without adding TGF-β. TGF-β-treated samples were applied as positive EMT controls and tested in parallel to find out if the radiation has a potentiating effect on the EMT induction. To evaluate the effect of the stromal component, the epithelial cells were irradiated in cocultures with stromal MRC-9 lung fibroblasts. On day 3 post treatment, the EMT markers: α-SMA, vimentin, fibronectin, and E-cadherin, were analyzed. The oxidative stress levels were evaluated by 8-oxo-dG analysis in both epithelial and fibroblast cells. The protracted exposure to low Linear Energy Transfer (LET) radiation at the total absorbed dose of 1 Gy was able to induce changes suggestive of EMT. The results show that the presence of the stromal component and its signaling (TGF-β) in the cocultures enhances the EMT. Radiation had a minor cumulative effect on the TGF-β-induced EMT with both doses. The oxidative stress levels were higher than the background in both epithelial and stromal cells post chronic irradiation (0.1 and 1 Gy); as for the BEAS-2B cell line, the increase was statistically significant. We suggest that the induction of EMT in bronchial epithelial cells by radiation requires more than single acute exposure and the presence of stromal component might enhance the effect through free radical production and accumulation.

Direct and bystander effects in human blood lymphocytes exposed to 241Am alpha particles and the relative biological effectiveness using chromosomal aberration and micronucleus assay

Purpose: It is important to understand the significance of alpha (α) radiation-induced bystander effects (RIBE) and its relative biological effectiveness (RBE); this is because the phenomenon is not universal and the mechanism is unclear and because the RBE is widely varying and projected to be very high.Materials and methods: Isolated lymphocytes from healthy volunteers (n = 10) were exposed to either low fluence α-particles (241Am), γ-rays (60Co), or X-rays (225 kVp and 6 MV). Co-culture methodology was employed to investigate bystander effects (BEs). Chromosomal aberrations (CA) and micronucleus (MN) formation were used to study the BE and calculated RBE.Results: Lymphocytes directly exposed to the types of radiation used showed a dose-dependent increase in the frequency of CA and MN; dose independent increases in the frequency of these chromosomal damages in co-cultured bystander cells, implies that all three types of radiation-induced a BE. The calculated RBE at the level of 5% induced aberrations varied between 9 and 20.Conclusion: The magnitude of low fluence α-particle induced RIBE is higher than in low LET (linear energy transfer) radiation. The RBE also varies depending upon the endpoints used and adds up to targeted effects. Since the endpoint of CA is considered as an important and early marker of risk prediction, the RIBE and RBE using CA as a marker are relevant for radiation protection purposes.

Neutron-induced Rat Mammary Carcinomas Are Mainly of Luminal Subtype and Have Multiple Copy Number Aberrations.

Neutrons are used as a type of high linear energy transfer (LET) radiation and they have stronger carcinogenic effects compared to low LET radiation. We sought to clarify the features of mammary carcinomas for which the incidence increases when these were exposed to neutron radiation. We compared mammary carcinomas from female Sprague-Dawley rats irradiated at 7 weeks of age with 0.485 Gy neutron beams or 0.5-Gy γ rays, with carcinomas of non-irradiated rats. Tumors were classified into luminal and non-luminal subtypes based on immunohistochemistry, while their copy number aberrations were determined using microarrays. Neutrons and γ rays significantly increased the incidence of luminal carcinomas. The carcinomas in the three groups contained multiple aberrations affecting 46 genes for which mutations have been reported in human breast cancer. Neutrons and γ rays increase the incidence of luminal mammary carcinoma in rats, probably via genetic aberrations similar to those found in human breast cancer patients.

Abstract P3-12-21: Development of peptide-based targeted α-therapy for triple negative breast cancer

Abstract Triple-negative breast cancer (TNBC) is associated with a poorer prognosis, including a higher potential to metastasize and a decrease in the 5-year survival rate as compared to other breast cancer subtypes (77% vs. 93%). The poor prognosis is partially due to the lack of targeted treatments for TNBC, highlighting the need to develop targeted therapies for TNBC. Alpha-emitting radionuclides, such as Actinium-225, provide high linear energy transfer (LET) radiation. Clinical and pre-clinical studies have shown that targeted alpha-therapy is a highly potent treatment for metastatic cancer. Peptides and peptidomimetics are minimally immunogenic and have rapid tissue and tumor penetration, and rapid clearance from non-target tissues, providing an attractive platform for targeted therapeutic agent. The RGD peptide has been shown to have a high affinity for αvβ3, which has been implicated in TNBC. The purpose of these studies is to investigate the potential of modified RGD peptide scaffolds to deliver 225Ac to triple negative breast cancer cells for targeted alpha therapy. Methods DOTA-cyclo-RGD(fK) and DOTA-cyclo-RGD(fK) dimer were labeled with Indium-111, a SPECT imaging surrogate for 225Ac, and Actinium-225. The resulting labeled agents were evaluated in vitro, including binding affinity assays (111In) and colony formation assays (225Ac) that are underway using the MDA-MB-231 cell line. Biodistribution experiments were performed in athymic nude mice bearing MDA-MB-231 tumors to compare the distribution and pharmacokinetics of the 111In-labeled RGD peptide scaffolds in vivo. Alpha camera imaging evaluated the microscale distribution of 225Ac-DOTA-cyclo-RGD(fK) in non-tumor bearing mice. Results The saturation binding assay of 111In-labeled DOTA-cyclo-RGD(fK) and DOTA-cyclo-RGD(fK) dimer demonstrated selective binding and nanomolar affinity for αvβ3. Selective targeting of αvβ3was further demonstrated in vivo for both 111In-labeled RGD agents. The 111In-labeled DOTA-cyclo-RGD(fK) demonstrated significantly higher tumor uptake at 30 minutes compared to the dimer (5.3 ± 2.9 vs. 3.0 ± 1.4 %ID/g). The 111In-DOTA-cyclo-RGD(fK) dimer was better retained in the tumor over 6 hours with significantly higher uptake at the 6-hour time point (1.2 ± 0.4 vs. 2.8 ± 1.1 %ID/g). Furthermore, the dimer had significantly higher uptake in the kidney and liver over a 6-hour window as compared to 111In-DOTA-cyclo-RGD(fK). However, both 111In-labeled RGD agents demonstrated rapid clearance from normal organs. Alpha camera images of the 225Ac-labeled dimer supported the rapid clearance from the normal tissues, with the majority of the agents being cleared within the first 90 minutes. Conclusion Modified RGD peptides were successfully labeled with Indium-111 and Actinium-225. The resulting agents were shown to successfully target αvβ3 selectively both in vitro and in vivo. These studies provide encouraging data to support the development and optimization of the RGD platform for αvβ3-targeted alpha therapy to treat triple negative breast cancer. Future works will investigate the therapeutic efficacy, macro- and microscale dosimetry, and toxicity of the developed 225Ac-labeled αvβ3-targeted agents as well as explore the optimization of the RGD scaffold for improved pharmacokinetics with 225Ac. Citation Format: Nedrow JR, Cortez A, Josefsson A, Sgouros G. Development of peptide-based targeted α-therapy for triple negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-12-21.