Estimation of low-dose radiation-responsive proteins in the absence of genomic instability in normal human fibroblast cells

Purpose: Low-dose radiation has various biological effects such as adaptive responses, low-dose hypersensitivity, as well as beneficial effects. However, little is known about the particular proteins involved in these effects. Here, we sought to identify low-dose radiation-responsive phosphoproteins in normal fibroblast cells.

Materials and methods: We assessed genomic instability and proliferation of fibroblast cells after γ-irradiation by γ-H2AX foci and micronucleus formation analyses and BrdU incorporation assay, respectively. We screened fibroblast cells 8?h after low-dose (0.05?Gy) γ-irradiation using Phospho Explorer Antibody Microarray and validated two differentially expressed phosphoproteins using Western blotting.

Results: Cell proliferation proceeded normally in the absence of genomic instability after low-dose γ-irradiation. Phospho antibody microarray analysis and Western blotting revealed increased expression of two phosphoproteins, phospho-NFκB (Ser536) and phospho-P70S6K (Ser418), 8?h after low-dose radiation.

Conclusions: Our findings suggest that low-dose radiation of normal fibroblast cells activates the expression of phospho-NFκB (Ser536) and phospho-P70S6K (Ser418) in the absence of genomic instability. Therefore, these proteins may be involved in DNA damage repair processes.     

Identification of cellular responses to low-dose radiation by the profiling of phosphorylated proteins in human B-lymphoblast IM-9 cells

Purpose: The aim of this study was to explore the potential for radiation-specific signaling of various LDIR-induced effects in human B-lymphoblast IM-9 cells.

Materials and methods: Human lymphoblast IM-9 cells were exposed to ionizing radiation at 0.1 and 2?Gy using a ¹³⁷Cs γ-irradiator at a dose rate of 0.8?Gy/min. Cell viability and DNA fragmentation were determined using MTT assay and TUNEL assay at 24?h after irradiation. Profiling of protein phosphorylation by radiation was identified using a phospho-antibody array at 4?h after irradiation and Dataset of the profiling was analyzed by IPA.

Results: Cell survival and apoptotic signaling were not affected by 0.1?Gy of radiation, whereas 2?Gy induced cellular damage. The analysis of low-dose ionizing radiation (LDIR) or high-dose ionizing radiation (HDIR)-specific responses by IPA generated different results. Various cell maintenance functions were only apparent following the analysis of increased protein phosphorylation by LDIR, whereas several cancer formation- and development-related functions were only detected following the analysis of increased protein phosphorylation by HDIR.

Conclusions: The LDIR-induced protein phosphorylation patterns might be involved in various cell survival responses or cellular maintenance functions, which provide important insight into our understanding of the different effects of LDIR and HDIR.     

A biosafety evaluation of synchrotron radiation X-ray to skin and bone marrow: single dose irradiation study of rats and macaques

Purpose: Very limited experimental data is available regarding the safe dosages related to synchrotron radiation (SR) procedures. We used young rats and macaques to address bone marrow and skin tolerance to various doses of synchrotron radiation.

Methods: Rats were subjected to 0, 0.5, 2.5, 5, 25 or 100?Gy local SR X-ray irradiation at left hind limb. Rat blood samples were analyzed at 2–90 days after irradiation. The SR X-ray irradiated skin and tibia were sectioned for morphological examination. For non-human primate study, three male macaques were subjected to 0.5 or 2.5?Gy SR X-ray on crus. Skin responses of macaques were observed.

Results: All rats that received SR X-ray irradiation doses greater than 2.5?Gy experienced hair loss and bone-growth inhibition, which were accompanied by decreased number of follicles, thickened epidermal layer, and decreased density of bone marrow cells (p?<?0.05). Macaque skin could tolerate 0.5?Gy SR X-ray but showed significant hair loss when the dose was raised above 2.5?Gy.

Conclusion: The safety threshold doses of SR X-ray for rat skin, bone marrow and macaque skin are between 0.5 and 2.5?Gy. Our study provided essential information regarding the biosafety of SR X-ray irradiation.     

Inducing mutations through γ-irradiation in seeds of Mucuna pruriens for developing high L-DOPA-yielding genotypes

Purpose: To develop elite genotypes in Mucuna pruriens (L.) DC with high L-DOPA (L-3, 4 dihydroxyphenylalanine) yields, with non-itching characteristics and better adaptability by applying γ-irradiation. Molecular and chemical analysis was performed for screening based on specific characteristics desired for developing suitable genotypes.

Materials and methods: Developed, mutant populations were analyzed for L-DOPA % in seeds through TLC (thin layer chromatography), and the results obtained were validated with the HPLC (High performance liquid chromatography). The DNA (Deoxyribonucleic acid) was isolated from the leaf at the initial stage and used for DNA polymorphism. RNA (Ribonucleic acid) was isolated from the leaf during maturity and used for expression analysis.

Results: The selected mutant T-I-7 showed 5.7% L-DOPA content compared to 3.18% of parent CIM-Ajar. The total polymorphism obtained was 57% with the molecular marker analysis. The gene expression analysis showed higher fold change expression of the dopadecarboxylase gene (DDC) in control compared to selected mutants (T-I-7, T-II-23, T-IV-9, T-VI-1).

Conclusion: DNA polymorphism was used for the screening of mutants for efficient screening at an early stage. TLC was found suitable for the large-scale comparative chemical analysis of L-DOPA. The expression profile of DDC clearly demonstrated the higher yields of L-DOPA in selected mutants developed by γ-irradiation in the seeds of the control.     

Synergistic effect of Ebselen and gamma radiation on breast cancer cells

Purpose: To explore the synergistic effect of a seleno-organic compound Ebselen (Ebs) and/or γ-radiation to exert antitumor effects on human breast cancer (MCF-7) cell line in vitro.

Materials and methods: Ebs cytotoxicity at various concentrations (10, 25, 50 and 75 μg), cell proliferation and clonogenic assay of Ebs and/or γ-radiation (at 1, 3 and 6?Gy), expression of p-IκBα and NF-κB, inflammatory cytokines levels (TNF-α, IL-2, INF-γ, IL-10 and TGF-β), apoptotic factors (Caspase-3, Granzyme-B and TRAIL) and angiogenic factor (VEGF) were investigated.

Results: The results showed that the effective dosage of this combination was observed at 25 μg/ml of Ebs with γ-radiation at 6?Gy. Data displayed a significant reduction in NF-κB mRNA along with an elevation in granzyme-B mRNA and TRAIL mRNA expression. Furthermore, protein expression of caspase-3 was elevated, whereas p-IκBα and p-NF-κB(p65) protein expression was reduced significantly. Also, a significant decline in TNF-α, IL-2, INF-γ, TGF-β with a significant increase in IL-10 levels were revealed. Meanwhile, a significant decrease in VEGF level and proliferation capacity were observed.

Conclusions: We conclude that a combination of Ebs with radiotherapy has a major antitumor efficiency in inducing apoptosis and inhibiting cancer cell progression, due to the synergistic effect in regulating gene and protein expression, and in a modulating response of pro-and anti-inflammatory cytokines.     

Altered expression of a metformin-mediated radiation response in SA-NH and FSa tumor cells treated under in vitro and in vivo growth conditions

Purpose: To assess the radiosensitizing effect of the biguanide drug metformin used alone or in combination with reactive oxygen species (ROS) modifying agents N-acetyl-L-cysteine (NAC) or emodin, and contrasted to the mitochondrial complex 1 inhibitor rotenone in altering the radiation responses of the p53 wild-type SA-NH and p53 mutant FSa mouse tumor lines grown either in vitro or in vivo.

Materials and methods: Tumor cells were grown to confluence in vitro and exposed to a single 4?Gy dose in the presence or absence of metformin (5?mM) and ROS modifiers or to 10?Gy with or without metformin as tumors in the flanks of C3H mice using a tumor growth delay assay.

Results: Both metformin and rotenone protected SA-NH (p?<?.001) while sensitizing FSa (p?<?.001) to 4?Gy. Neither NAC nor emodin altered metformin’s action. Metformin was also directly toxic to FSa cells (p?=?.002). In contrast, in vivo metformin (250?mg/kg) sensitized both SA-NH (9-day growth delay, p?<?.05) and FSa (4-day growth delay, p?<?.05) tumors if administered 1?h before irradiation.

Conclusion: Metformin effects on tumor cells measured under in vitro conditions may differ from those determined in vivo due to p53 and heterogeneous environmental factors.     

Irradiation biology of male brown marmorated stink bugs: is there scope for the sterile insect technique?

Purpose: Brown marmorated stink bugs, Halyomorpha halys Stål (Hemiptera: Pentatomidae), are regularly intercepted, but there are few eradication tools. Currently, no sterile insect technique program exists for Hemiptera.

Materials and methods: Adult males were irradiated at 4–60?Gy, mated and their progeny reared for two generations, with mortality assessed at F₁ egg, F₁ adult and F₂ egg stages.

Results: The F₁ eggs showed a dose response to irradiation between 4 and 36?Gy, with 97% sterility at 16?Gy, and higher doses producing complete egg mortality. Only rare F₁ survivors had progeny, but the F₂ generation showed identical responses between maternal and paternal lines; most egg batches showed either very low or very high mortality. Irradiation with 16?Gy resulted in 98.5% sterility, cumulative over F₁ and F₂.

Conclusions: Lack of a dose response at the F₂ generation precludes the use of irradiation-induced inherited sterility. The conventional sterile insect technique appears possible by irradiation of males from ～12 to 16?Gy. The effect of radiation dose on females is not known, thus we cannot conclude whether bi-sex release is feasible so for now the release of males only is recommended. More work is needed on the competitive fitness of irradiated males, and logistics such as mass rearing or field collection, in order to determine the feasibility of the approach.     

The effect of radiation dose on the onset and progression of radiation-induced brain necrosis in the rat model

Purpose: To provide a comprehensive understanding of how the selection of radiation dose affects the temporal and spatial progression of radiation-induced necrosis in the rat model.

Materials and methods: Necrosis was induced with a single fraction of radiation exposure, at doses ranging between 20 and 60?Gy, to the right hemisphere of 8-week-old Fischer rats from a linear accelerator. The development and progression of necrosis in the rats was monitored and quantified every other week with T1- and T2-weighted gadolinium contrast-enhanced MRI studies.

Results: The time to onset of necrosis was found to be dose-dependent, but after the initial onset, the necrosis progression rate and total volume generated was constant across different doses ranging between 30 and 60?Gy. Radiation doses less than 30?Gy did not develop necrosis within 33 weeks after treatment, indicating a dose threshold existing between 20 and 30?Gy.

Conclusion: The highest dose used in this study led to the shortest time to onset of radiation-induced necrosis, while producing comparable disease progression dynamics after the onset. Therefore, for the radiation-induced necrosis rat model using a linear accelerator, the most optimum results were generated from a dose of 60?Gy.     

Whole body proton irradiation causes acute damage to bone marrow hematopoietic progenitor and stem cells in mice

Purpose: Exposure to proton irradiation during missions in deep space can lead to bone marrow injury. The acute effects of proton irradiation on hematopoietic stem and progenitor cells remain undefined and thus were investigated.

Materials and methods: We exposed male C57BL/6 mice to 0.5 and 1.0?Gy proton total body irradiation (proton-TBI, 150?MeV) and examined changes in peripheral blood cells and bone marrow (BM) progenitors and LSK cells 2 weeks after exposure.

Results: 1.0?Gy proton-TBI significantly reduced the numbers of peripheral blood cells compared to 0.5?Gy proton-TBI and unirradiated animals, while the numbers of peripheral blood cell counts were comparable between 0.5?Gy proton-TBI and unirradiated mice. The frequencies and numbers of LSK cells and CMPs in BM of 0.5 and 1.0?Gy irradiated mice were decreased in comparison to those of normal controls. LSK cells and CMPs and their progeny exhibited a radiation-induced impairment in clonogenic function. Exposure to 1.0?Gy increased cellular apoptosis but not the production of reactive oxygen species (ROS) in CMPs two weeks after irradiation. LSK cells from irradiated mice exhibited an increase in ROS production and apoptosis.

Conclusion: Exposure to proton-TBI can induce acute damage to BM progenitors and LSK cells.     

Thoracic gamma irradiation-induced obesity in C57BL/6 female mice

Purpose: To investigate the late effects of thoracic region irradiation (TRI) on mouse body weight.

Materials and methods: Female C57BL/6 mice were divided into nonirradiated, 5?Gy total body irradiation, 9?Gy sub-total body irradiation, and 12.5?Gy thoracic region irradiation (TRI) groups. Changes in mouse weight were monitored every other week at similar time points for 12 months. The anatomical characteristics of abdominal visceral fat distribution were recorded, and mitochondrial DNA copy number in the hearts and livers and lipid metabolic signaling in the liver were analyzed. Data were analyzed by one-way analysis of variance and a student’s t-test.

Results: TRI led to a significant increase (p?<?.001) in body weight that was dependent on time and individuals [42.1% of mice were overweight (50% increase in body weight) 4 months post-TRI and 100% of mice were overweight at 10 months post-TRI]. Gross anatomical features of abdominal visceral fat distribution and storage in radiation-induced overweight/severely overweight mice were similar to those of high fat diet-induced overweight/severely overweight mice. The mitochondrial genome of heart and liver tissues from overweight/severely overweight mice had significantly (p?<?.05) decreased functional mitochondrial DNA copy number (ratios decreased from 1 to 0.71 or 0.49, respectively) and significantly (p?<?.05) increased mitochondrial DNA mutations (ratios increased from 1 to 3.21 or 1.83, respectively). CPT1 and IRS2 lipid metabolic signaling was significantly (p?<?.05–.01) decreased for both mRNA (fold decrease from 1 to 0.60 or 0.55, respectively) and protein (fold decrease from 1 to 0.62 or 0.19, respectively).

Conclusions: TRI can cause mice to gain weight. These findings indicate that TRI can result in lipid metabolic abnormalities and provide a model to study the factors that result in these abnormalities.     

Radiation protection and mitigation potential of phenylbutyrate: delivered via oral administration

Purpose: Phenylbutyrate (PB), a histone deacetylase inhibitor (HDACi) has demonstrated radiation protection in both in vitro and in vivo models. Studies previously demonstrated that PB and other HDAC inhibitors could inhibit radiation lethality in vivo by subcutaneous (s.c) injection. The objective of this study was to test the ability of oral PB treatment to protect against or to mitigate acute gamma radiation-induced lethality in vivo.

Materials and methods: Human osteoblasts cells were used to evaluate radiation survival when PB was delivered pre- or post-radiation. A 30-day radiation lethality study was used to assess the radioprotective (pre-radiation) and radiomitigative (post-radiation) capability of PB. Possible mechanisms evaluated were antioxidant activity effects, HDAC inhibition, DNA damage, and hematological recovery.

Results: Treatment of HOS cells with PB 50?μM either before or after radiation increased radiation resistance as assessed by clonogenic survival. Western blot studies showed that PB treatment acetylated histones in vivo and ameliorated the radiation-induced reduction in acetylated histone-4 (H4). Pre-radiation oral administration of PB (10?mg/kg) provided radioprotection against gamma radiation (7–11.5?Gy) with a dose reduction factor of 1.25 (p?=?0.001). PB oral administration post-radiation provided moderate radiation mitigation against gamma radiation (7–11.5?Gy) and demonstrated a dose reduction factor of 1.18 (p?=?0.05). PB pre-radiation and post-radiation treatment was associated with significant elevations in neutrophils and platelets and attenuation of DNA damage.

Conclusions: These results indicate that oral PB has potential as a radiation protector and a radiation mitigator and that potential mechanisms of action include attenuation of DNA damage, antioxidant activity, and bone marrow protection.     

Melatonin prevents possible radiotherapy-induced thyroid injury

Purpose: We aimed to investigate the protective effect of melatonin in radiotherapy-induced thyroid gland injury in an experimental rat model.

Materials and methods: Thirty-two rats were divided into four groups: the control group, melatonin treatment group, radiotherapy group and melatonin plus radiotherapy group. The neck region of each rat was defined by simulation and radiated with 2 Gray (Gy) per min with 6-MV photon beams, for a total dose of 18?Gy. Melatonin was administered at a dose of 50?mg/kg through intraperitoneal injection, 15?min prior to radiation exposure. Thirty days after the beginning of the study, rats were decapitated and analyses of blood and thyroid tissue were performed.

Results: Tumor necrosis factor-α (TNF-α), interleukin-1 beta (IL-1β), thiobarbituric acid reactive substances (TBARS) and nitric oxide (NO) levels in the radiotherapy group were significantly higher than those in the melatonin plus radiotherapy group (p?<?.05), whereas interleukin-10 (IL-10) and glutathione (GSH) values were higher in the melatonin plus radiotherapy group (p?<?.05). The infiltration of inflammatory cells and percentage of apoptosis in the radiotherapy group were significantly higher than those in the melatonin plus radiotherapy group (p?<?.05).

Conclusions: Melatonin helped protect thyroid gland structure against the undesired cytotoxic effects of radiotherapy in rats.     

Partial alleviation of oxidative stress induced by gamma irradiation in Vigna radiata by polyamine treatment

Purpose: Environmental changes generate free radicals and reactive oxygen species (ROS) resulting in abiotic stress in plants. This causes alterations in germination, morphology, growth and development ultimately leading to yield loss. Gamma irradiation was used to experimentally induce oxidative damage in an important pulse crop Vigna radiata (L.) Wilczek or mung bean. Our research was aimed towards augmentation of oxidative stress tolerance through treatment with a group of aliphatic amines known as polyamines.

Materials and methods: We used sub-lethal doses of gamma irradiation to generate oxidative damage which was evaluated using Nitro blue tetrazolium (NBT) staining, total antioxidant activity, 1, 1-Diphenyl-2-picryl hydrazyl (DPPH) radical scavenging assay, proline content and lipid peroxidation. Changes in internal free polyamines and messenger ribonucleic acid (mRNA) expression of key rate-limiting S-adenosylmethionine decarboxylase (SAMDC) enzyme in polyamine biosynthetic pathway was studied using real-time polymerase chain reaction (PCR).

Results: We observed increased oxidative damage with higher irradiation dose which was partially alleviated by putrescine treatment. Internal levels of putrescine and spermidine increased with 1?mM (50 and 100?Gy) and 2?mM putrescine treatment. Expression of SAMDC also increased with putrescine treatment.

Conclusion: This study shows that treatment with putrescine can partially alleviate oxidative damage caused by gamma rays.     

Proteome analysis of irradiated endothelial cells reveals persistent alteration in protein degradation and the RhoGDI and NO signalling pathways

Purpose: Epidemiological studies indicate that radiation doses as low as 0.5?Gy increase the risk of cardiovascular disease decades after the exposure. The aim of the present study was to investigate whether this radiation dose causes late molecular alterations in endothelial cells that could support the population-based data.

Materials and methods: Human coronary artery endothelial cells were irradiated at 0.5?Gy (X-ray) and radiation-induced changes in the proteome were investigated after different time intervals (1, 7 and 14 d) using ICPL technology. Key changes identified by proteomics and bioinformatics were validated by immunoblotting and ELISA.

Results: The radiation-induced alteration of the endothelial proteome was characterized by sustained perturbation of Rho GDP-dissociation inhibitor (RhoGDI) and nitric oxide (NO) signalling pathways. At later time-points, this was accompanied by reduced proteasome activity, enhanced protein carbonylation indicating augmented oxidative stress, and senescence.

Conclusions: These molecular changes are indicative of long-term premature endothelial dysfunction and provide a mechanistic framework to the epidemiological data showing increased risk of cardiovascular disease at 0.5?Gy.     

Cytokine profile of breast cell lines after different radiation doses

Purpose: Ionizing radiation (IR) treatment activates inflammatory processes causing the release of a great amount of molecules able to affect the cell survival. The aim of this study was to analyze the cytokine signature of conditioned medium produced by non-tumorigenic mammary epithelial cell line MCF10A, as well as MCF7 and MDA-MB-231 breast cancer cell lines, after single high doses of IR in order to understand their role in high radiation response.

Materials and methods: We performed a cytokine profile of irradiated conditioned media of MCF10A, MCF7 and MDA-MB-231 cell lines treated with 9 or 23?Gy, by Luminex and ELISA analyses.

Results: Overall, our results show that both 9?Gy and 23?Gy of IR induce the release within the first 72?h of cytokines and growth factors potentially able to influence the tumor outcome, with a dose-independent and cell-line dependent signature. Moreover, our results show that the cell-senescence phenomenon does not correlate with the amount of ‘senescence-associated secretory phenotype’ (SASP) molecules released in media. Thus, additional mechanisms are probably involved in this process.

Conclusions: These data open the possibility to evaluate cytokine profile as useful marker in modulating the personalized radiotherapy in breast cancer care.     

Nano alterations of membrane structure on both γ-irradiated and stored human erythrocytes

Purpose: Storage and ionizing radiation of human red blood cells (RBC) produce alterations on RBC membranes and modify their normal shape and functionality. We investigated early morphological and biochemical changes in RBC due to those stressing agents at the nanoscale level and their impact on blood quality.

Materials and methods: Whole blood samples from healthy donors were γ-irradiated with 15, 25, 35, and 50?Gy. Non-irradiated and non-stored RBC were used as control samples. Irradiated blood samples were stored separately at 4?°C and analyzed immediately and after 5 and 13 d. Atomic force microscopy (AFM), osmotic fragility and Raman spectroscopy were used to detect morphological and biochemical changes.

Results: RBC function is challenged by both irradiation and storage. The storage procedure caused nanometric variations over the surface of RBC membrane for both irradiated and non-irradiated cells. The membrane of RBC became more fragile, while the biochemical fingerprint of hemoglobin (Hb) remained unaltered.

Conclusions: Our work shows that the irradiation procedure leads to an increase in the number and size of nanovesicles along with the dose. The functionality of RBC can be affected from changes in the roughness, becoming more fragile and susceptible to breakage.     

Potentiality of syringetin for preferential radiosensitization to cancer cells

Purpose: To examine the enhancing effects of syringetin on the radiosensitivity of normal and cancer cells, and the related mechanism.

Materials and methods: We used normal human lung and mouse fibroblasts as well as human lung and mouse cancer cells derived from the above normal fibroblasts. Cell radiosensitivity was measured using a colony formation assay. Apoptosis was analyzed with DAPI staining and Western blots. DNA lesions were analyzed with γH2AX immunofluorescent staining.

Results: The colony formation assay showed that syringetin enhanced radiosensitivity more effectively in cancer cells (H1299 and C3H/MCA clone 15) compared with normal cells (HFL-III and C3H/10T1/2). The radiosensitizing effect of syringetin was observed in mutated p53 and wild-type p53-transfected H1299 cells regardless of p53 status. Apoptosis was more frequently observed in X-ray-irradiated H1299 cells combined with syringetin compared with X-ray-only-treated cells. Enhanced apoptosis by syringetin was not observed in HFL-III cells. Western blot analysis showed that X-ray-induced Caspase-3 activation was enhanced by syringetin in H1299 cells. The number of X-ray-induced DNA double-strand breaks (DSB) measured by quantitative analysis of γH2AX foci was the same for H1299 cells treated with X-rays with or without syringetin.

Conclusions: This study supports the hypothesis that syringetin enhances radiosensitivity more effectively in cancer cells than in normal cells through enhancement of the Caspase-3-mediated apoptosis pathway. Syringetin could be useful in the development of novel efficacious radiosensitizers.     

Evaluation of thiol-disulphide homeostasis in radiation workers

Purpose: To evaluate thiol-disulphide homeostasis – a novel, easily calculated, readily available, and relatively cheap oxidative stress marker – in radiation workers and compare the results with healthy controls.

Materials and methods: A total of 108 participants were enrolled in the study including 63 hospital workers occupationally exposed to ionizing radiation in the units of interventional radiology, interventional cardiology and nuclear medicine. A control group consisted of 45 individuals staff in the same hospital. Serum thiol-disulphide homeostasis measurement was investigated via the spectrophotometric method newly described by Erel and Ne?elio?lu.

Results: The mean serum native thiol levels of radiation workers (528.96?±?86.42?μmol/l) was significantly lower than control subjects (561.05?±?104.83?μmol/l) (p?=?.045). The mean serum total thiol levels of radiation workers (547.70?±?91.50?μmol/l) was lower than control subjects (580.36?±?112.24?μmol/l). Nevertheless, there was no significant difference between total thiol of exposed workers and controls.

Conclusions: The results show that long-term low dose ionizing radiation may lead to oxidative stress and have side-effects in antioxidant thiol groups. We may suggest supporting radiation workers by safe antioxidant nutritional formulations and following up via both physical dosimetry and biodosimetric methods.     

Normal tissue complication probability modeling of radiation-induced sensorineural hearing loss after head-and-neck radiation therapy

Purpose: The aim of this study was to generate the dose–response curves by six normal tissue complication probability (NTCP) models and ranking the models for prediction of radiation induced sensorineural hearing loss (SNHL) caused by head and neck radiation therapy (RT).

Materials and methods: Pure tone audiometry (PTA) was performed on 70 ears of patients for 12 months after the completion of RT. The SNHL was defined as a threshold shift ≤15?dB at two contiguous frequencies according to the common toxicity criteria for adverse events scoring system. The models evaluated were: Lyman and Logit; Mean Dose; relative seriality (RS); Individual critical volume (CV); and population CV models. Maximum likelihood analysis was used to fit the models to experimental data. The appropriateness of the fit was determined by the two-sample Kolmogorov–Smirnov test. Ranking of the models was made according to Akaike’s information criterion.

Results: The dose of 50% complication rate (D₅₀) was 51–60?Gy. Three of the examined models fitted well with clinical data in a 95% confidence interval. The RS model was ranked as the best model of prediction for radiation induced SNHL.

Conclusions: Cochlea shows a different behavior against different NTCP models; it may be due to its small size.