Fibronectin and laminin increase resistance to ionizing radiation and the cytotoxic drug Ukrain® in human tumour and normal cells in vitro

Purpose: Cell–extracellular matrix (ECM) interactions are thought to mediate drug and radiation resistance. Dependence of cell survival, β1‐integrin expression and cell cycling on the ECM proteins and β1‐integrin ligands fibronectin (FN) and laminin (LA) were examined in malignant and normal cells exposed to the cytotoxic drug Ukrain plus/minus irradiation.

Materials and methods: Human A549 lung cancer and MDAMB231 (MDA231) breast cancer cells and normal fibroblasts (HSF1) grown on FN, LA, bovine serum albumin (BSA) or polystyrene were treated with Ukrain (1?µg?ml^?1, 24?h) plus/minus irradiation (2–8?Gy) and the effects studied using colony formation assays, flow cytometry (β1‐integrin, DNA analysis) and adhesion assays.

Results: FN and LA reduced the cytotoxic effect of single Ukrain treatment compared with polystyrene and BSA. FN and LA also abolished Ukrain‐dependent radiosensitization in A549 cells and decreased the radiosensitivity of MDA231 and HSF1 cells. Single Ukrain exposure on polystyrene significantly reduced β1‐integrin expression and promoted G2‐phase accumulation of A549 cells. In contrast, Ukrain‐treated MDA231 and HSF1 cells showed elevated β1‐integrin expression and no Ukrain‐specific cell cycle effect. Under Ukrain‐radiation exposure, irradiation, FN or LA abolished Ukrain‐mediated reduction of β1‐integrin expression and G2‐phase accumulation in A549 cells, whereas in MDA231 cells and fibroblasts β1‐integrin expression and cell cycle distribution were stabilized. Cell adhesion to FN or LA was significantly impaired (A549) or improved (MDA231, HSF1) upon Ukrain treatment.

Conclusions: The data corroborate the findings of other groups that cell adhesion‐mediated resistance to either single or combined drug and radiation exposure is tightly correlated to specific ECM proteins. By demonstrating a strong modulatory impact of FN and LA on the radiosensitivity‐modifying activity of the drug Ukrain, these findings are also highly important for the assessment of drug and radiation effects within in vitro cytotoxicity studies. The data give the first mechanistic insights into specific FN‐ and LA‐modulated cellular resistance mechanisms as well as into the important role for β1‐integrins using the unique cytotoxic and radiosensitivity‐modifying drug Ukrain.     

Cellular origin of ionizing radiation‐induced NF‐κB activation in vivo and role of NF‐κB in ionizing radiation‐induced lymphocyte apoptosis

Purpose: To investigate the cellular origin of ionizing radiation (IR)‐induced NF‐κB activation in vivo and the role of NF‐κB in IR‐induced lymphocyte apoptosis.

Materials and methods: NF‐κB activities were analysed by gel shift/supershift assay in isolated murine T‐ and B‐cells, macrophages (M?) and tissues from normal and T‐ and B‐cell‐deficient Rag1 mice with or without exposure to IR. IR‐induced lymphocyte apoptosis was determined by analysis of 3,3′‐dihexyloxacarbocyanine iodide (DiOC₆) uptake, annexin‐V staining and the sub‐G0/1 population, or by TUNEL assay.

Results: The results showed that IR activated NF‐κB in lymphocytes, including both T‐ and B‐cells, but failed to do so in M?. Furthermore, T‐ and B‐cell‐deficient Rag1 mice exposed to IR exhibited a significant reduction in NF‐κB activation as compared with normal mice. Although NF‐κB1 (p50) gene knockout or NF‐κB decoy oligonucleotide treatment specifically inhibited IR‐induced lymphocyte NF‐κB activation, they had no significant effect on IR‐induced lymphocyte apoptosis.

Conclusions: This finding suggests that lymphocytes are the main cellular origin of IR‐induced NF‐κB activation in vivo. However, NF‐κB activation has no significant effect on IR‐induced lymphocyte apoptosis.     

Telomere shortening and ionizing radiation: A possible role in vascular dysfunction?

Abstract

Purpose: In recent years, growing epidemiological evidence has linked ionizing radiation exposure to cardiovascular atherosclerotic disease. However, there are still major gaps in the knowledge of the molecular mechanisms of radiation-induced vascular disease, especially for low-dose levels. Telomeres, repetitive DNA sequences of (TTAGGG)_n located at the ends of eukaryotic chromosomes, play a role in regulating vascular aging, and shorter leukocyte telomere length has been demonstrated to predict cardiovascular disease and mortality. There is also evidence supporting the crucial role of telomeres in the formation of chromosome and chromatid aberrations induced by ionizing radiation.

Conclusions: The purpose of the present paper is to review the recent advances in the biological mechanisms determining telomere length erosion after ionizing radiation exposure as well as to examine the hypothesis that telomere shortening may be the crucial mediator leading to detrimental vascular effects after ionizing radiation exposure.     

Science to practice: can antioxidant supplements protect against the possible harmful effects of ionizing radiation from medical imaging?

Deshpande et al (1) have shown that P-selectin-targeted microbubbles (MBs) can be used to monitor the expression of this molecule as a marker of inflammation in a murine model of inflammatory bowel disease (IBD). If these results can be reproduced in future clinical trials, contrast material–enhanced ultrasound (US) of targeted MBs (US molecular imaging) will enable accurate monitoring of inflammation and, specifically, response to IBD therapy, which should improve clinical outcomes.     

Injury surveillance in male professional football; is medical staff reporting complete and accurate?

Since the 2000 season, an injury surveillance system has been established to monitor injury risk and injury patterns in the Norwegian professional football league. The aim of this study was to assess the accuracy of routine injury registration performed by medical staff in professional football. The team medical staff completed injury registration forms on a monthly basis throughout the 2007 season (January–October). Players were interviewed at the end of the season (October/November) about all injuries that occurred from July through September. Thirteen of fourteen teams, 296 of 310 A‐squad players were interviewed. An injury was recorded when a player was unable to take fully part in football training or match the day after injury. A total of 174 injuries were registered, 123 acute injuries and 51 overuse injuries. Of these, 141 were reported by medical staff and 122 by players. Eighty‐nine injuries (51%) were registered using both methods, 52 (30%) by medical staff only and 33 (19%) by player interviews only. Prospective injury surveillance by team medical staff in Norwegian male professional football underestimates the incidence of time‐loss injuries by at least one‐fifth.     

Possible role of elevation of glutathione in the acquisition of enhanced proliferation of mouse splenocytes exposed to small-dose γ-rays

Purpose : To examine the relation between the induction of an increased glutathione level and the elevated proliferative response of mouse splenocytes by a small dose of γ-rays. Materials and methods : Male ICR strain mice, 7 weeks of age, were divided into irradiated and non-irradiated control groups. Irradiation was done with γ-rays from a 137 Cs source at a dose of 50cGy (1.11Gy/min). Glutathione content in the splenocytes was measured using a modified spectrophotometric technique. Concanavalin A (Con A)-induced proliferative response of the splenocytes after whole-body γ-ray irradiation was estimated from the 3 H-thymidine incorporation into the cells. Results : The glutathione level in mouse splenocytes increased 2h after whole-body γ-ray irradiation at 50 cGy, peaked at 4h and thereafter decreased almost to the zero-time level by 12-h postirradiation. A significant enhancement of Con A-induced proliferation was observed in the splenocytes obtained from the wholebody-irradiated animals between 2h and 6h post-irradiation. Glutathione exogenously added to splenocytes obtained from normal mice enhanced the Con A-induced proliferation of splenocytes in a dose-dependent manner. This enhancement was completely blocked by buthionine sulfoximine, a specific inhibitor of the de novo pathway of glutathione synthesis. Conclusions : The induction of endogenous glutathione immediately after low-dose γ-ray irradiation is at least partially responsible for the enhancement of immune function, and may throw light on the mechanisms of carcinostatic effects induced by low dose ionizing radiation.     

mBAND analysis of chromosome aberrations in lymphocytes exposed in vitro to α-particles and γ-rays

Purpose:?To investigate the profiles of chromosome damage induced in vitro by exposure to α-particles and γ-rays.

Materials and methods:?Human peripheral blood lymphocytes were exposed to three dose regimes: α-particle doses of 0.2 and 0.5 Gy and a γ-ray dose of 1.5 Gy. After culturing for 47 hours, chromosome aberrations involving the number 5 chromosomes were identified using a multi-coloured banding (mBAND) technique.

Results:?Analysis of the frequencies of chromosome 5 breaks within aberrant cells and within aberrant number 5 chromosomes demonstrated that α-particle irradiation is more likely to result in multiple breaks in a chromosome than γ-irradiation. Additionally, overdispersion was observed for all doses for the distribution of breaks amongst all cells analysed and breaks amongst total number 5 chromosomes, with this being greatest for the 0.2 Gy α-particle dose. The ratio of interchanges to intrachanges (F ratio) was 1.4 and 2.4 for 0.2 and 0.5 Gy α-particles respectively and 5.5 for 1.5 Gy γ-rays. Evaluation of simple versus complex exchanges indicated ratios of 1.9 and 2.7 for 0.2 and 0.5 Gy α-particles respectively and 10.6 for 1.5 Gy γ-rays. The majority of the intrachanges involving chromosomes 5 induced by α-particle radiation were associated with more complex exchanges.

Conclusions:?This study has confirmed that exchanges induced by exposure to high linear energy transfer (LET) α-particle radiation comprise a greater proportion of intrachanges than those induced by exposure to low LET γ-rays. However, since the majority of these are associated with complex rearrangements and likely to be non-transmissible, this limits their applicability as a marker of past in vivo exposure.     

Occupational exposure to ionizing radiation has no effect on T‐ and B‐cell total counts or percentages of helper,cytotoxic and activated T‐cell subsets in the peripheral circulation of male radiation workers

Purpose: To investigate changes in immune cell subsets in the peripheral circulation of a male population occupationally exposed to ionizing radiation.

Materials and methods: Peripheral blood samples were taken from 194 male workers with cumulative exposures of >200?mSv (mean exposure 331.5?mSv, mean age 51 years) and from a reference population of 131 male workers with cumulative exposures of <27.5?mSv (mean exposure 13.9?mSv, mean age 47 years). Samples were analysed by flow cytometry for T‐ and B‐cell total counts and for the T‐cell subset percentages of CD4⁺ (helper T‐cells), CD8⁺ (cytotoxic T‐cells) and CD3⁺/HLA‐DR⁺ (activated T‐cells).

Results: Comparison of the >200 and <27.5?mSv exposure groups using linear regression analysis showed no statistically significant differences between the two groups for T‐cell total count, B‐cell total count or for percentages of the T‐cell subsets CD4⁺, CD8⁺ or CD3⁺/HLA‐DR⁺ and CD4⁺:CD8⁺. However, statistically significant increases in both T‐ and B‐cell total counts were observed within the two exposure groups and data pooled from both groups when non‐smokers (never and ex‐smokers) were compared with current smokers. For pooled data T‐cell total count increased in smokers by 35% (p=0.0001) and B‐cell total count increased by 37% (p=0.0004).

Conclusions: No significant immunological effects were observed in male radiation workers with cumulative exposures of >200?mSv when compared with a reference population with cumulative exposures of <27.5?mSv, although highly significant increases in both T‐ and B‐cell total counts were observed in smokers compared with non‐smokers.     

How to combine hygiene and radiation protection for radiopharmaceuticals preparation? Analysis in France and propositions

Radiopharmaceuticals for intravenous administration are considered as sterile medicinal products. Their preparation in hospitals involves adherence to regulations on radiation protection as well as to sterility requirements for parenteral administration. These two basic aspects are often opposite, making the working conditions difficult to define. Official texts that have included hygiene and radiation protection do not precisely state how to combine these two aspects in practice. Thus, after an analysis of the bibliography available, this review will show that even if hospital radiopharmacy departments in France are not able to work in total aseptic environments, some measures can be taken in order to improve preparation conditions.     

Positron-emission tomography CT to identify local recurrence in stage I lung cancer patients 1 year after stereotactic body radiation therapy

Purpose

To evaluate the diagnostic value of positron-emission tomography/computed tomography (PET/CT) in stage I lung cancer patients treated with stereotactic body radiation therapy (SBRT), who have suspicious or unclear local recurrence findings in CT 1 year after treatment.

Patients and methods

A group of 29 patients with unclear or suspicious CT findings 1 year after SBRT were examined with PET/CT. The ability of standard uptake values (SUV_max, SUV_mean and posttherapeutic reduction in SUV) to detect local failure and identify patients at a high risk of disease-specific death was evaluated using logrank statistics. Histology and clinical follow-up were the gold standards for local recurrence.

Results

SUV_mean greater than 3.44 (p?=?0.001); SUV_max greater than 5.48 (p?=?0.009) or a relative reduction in SUV_mean or SUV_max of less than 43 (p?=?0.030) or 52?% (p?=?0.025), respectively, was indicative of local recurrence. These parameters also correlated with an increased risk of disease-specific death: SUV_mean greater than 2.81 (p?=?0.023); SUV_max greater than 3.45 (p?=?0.007) or a relative reduction in SUV_mean or SUV_max of less than 32 (p?=?0.015) or 52?% (p?=?0.013), respectively, was indicative of an increased risk of disease-specific death.

Conclusion

PET/CT performed 1 year after SBRT can reliably identify local recurrence and therefore help to clarify unclear CT findings. As posttherapeutic glucose metabolism also correlates with disease-specific survival, PET/CT may help to stratify lung cancer patients for additional treatment 1 year after SBRT.     

Post‐irradiation approaches to treatment of radiation injuries in the context of radiological terrorism and radiation accidents: a review

Purpose: Events of the recent past have focused attention on the possibility of radiological (nuclear) terrorism and on the implications of such terrorist threats for radiation accident preparedness. This review discusses recent advances in the knowledge about how radiation injuries from such events might be treated pharmacologically, and the practical barriers to clinical utilization of these approaches.

Conclusions: A wide range of pharmacological approaches are being developed in the laboratory that could greatly expand the ability to treat acute and chronic radiation injuries. However, there are currently a variety of practical and legal barriers that would prevent the actual clinical use of most of the approaches. There are also the potential weaknesses in most of the current programmes for dealing with the consequences of radiation accidents or nuclear terrorism, including the absence of widespread radiation biodosimetry capabilities and the resulting inability to triage. If a major radiation accident or terrorist event occurs, the lack of biodosimetry and treatment capabilities will be compounded by widespread public fear of ‘radiation’.     

DNA damage in cultured skin microvascular endothelial cells exposed to gamma rays and treated by the combination pentoxifylline and α-tocopherol

Purpose: This in vitro study aims at evaluating the effect of the combination of pentoxifylline (PTX) and trolox (Tx), the water-soluble analogue of α-tocopherol, on the oxidative state and DNA damage in dermal microvascular endothelial cells exposed to doses up to 10 Gy of ionizing radiation.

Materials and methods: Confluent primary cultures of dermal endothelial cells were gamma irradiated at 3 and 10 Gy, and 0.5 mM of both drugs, PTX and Tx, was added either before (15 min) or after (30 min or 24 h) irradiation. Reactive oxygen species (ROS), measured by the dichlorodihydrofluorescein diacetate assay, and DNA damage, assessed by the comet and micronucleus assays, were measured at different times after exposure (0 – 21 days).

Results: The PTX/Tx treatment decreased the early and delayed peak of ROS production by a factor of 2.8 in 10 Gy-irradiated cells immediately after irradiation and the basal level by a factor of 2 in non-irradiated control cells. Moreover, the level of DNA strand breaks, as measured by the comet assay, was shown to be reduced by half immediately after irradiation when the PTX/Tx treatment was added 15 min before irradiation. However, unexpectedly, it was decreased to a similar extent when the drugs were added 30 min after radiation exposure. This reduction was accompanied by a 2.2- and 3.6-fold higher yield in the micronuclei (MN) frequency observed on days 10 and 14 post-irradiation, respectively.

Conclusion: These results suggest that oxidative stress and DNA damage induced in dermal microvascular endothelial cells by radiation can be modulated by early PTX/Tx treatment. These drugs acted not only as radical scavengers, but they were also responsible for the increased MN frequency in 10 Gy-irradiated cells. Thus, these drugs may cause a possible interference with DNA repair processes.     

Upregulated epithelial junction expression represents a novel parameter of the epithelial radiation response to fractionated irradiation in oral mucosa

Purpose

During head and neck cancer treatment, the radiation response of the oral mucosa represents a frequent early side effect. Besides radiation-induced inhibition of proliferation, various other cellular responses occur. The radiation response of adherens and tight junction proteins was so far mostly investigated with large single-dose irradiation protocols, in vivo and in vitro. Therefore, the current study was initiated to investigate the impact of daily fractionated irradiation on the expression of adherens and tight junction proteins in vivo.

Materials and methods

Fractionation with 5?×?3?Gy/week (days 0–4, 7–11) was given to the snouts of mice. Groups of 5 animals per day were euthanized every second day between day 0 (unirradiated controls) and day 14, and their tongues subjected to histological processing. Adherens junction marker (β-catenin and E?cadherin) and tight junction marker (claudin-1 and occludin) expression was analysed in the oral mucosa of unirradiated controls and during two weeks of fractionated irradiation.

Results

Adherens as well as tight junction marker proteins were rapidly and consistently upregulated in both the germinal as well as the functional layer of the oral mucosa. This represents a previously unknown parameter of the epithelial radiation response to clinically relevant fractionation protocols.

Conclusion

Fractionated irradiation significantly enhanced the expression of all proteins investigated. This study revealed a new parameter of the epithelial radiation response to fractionated irradiation.

     

Automated tube voltage adaptation in head and neck computed tomography between 120 and 100 kV: effects on image quality and radiation dose

Introduction

Low tube voltage allows for computed tomography (CT) imaging with increased iodine contrast at reduced radiation dose. We sought to evaluate the image quality and potential dose reduction using a combination of attenuation based tube current modulation (TCM) and automated tube voltage adaptation (TVA) between 100 and 120 kV in CT of the head and neck.

Methods

One hundred thirty consecutive patients with indication for head and neck CT were examined with a 128-slice system capable of TCM and TVA. Reference protocol was set at 120 kV. Tube voltage was reduced to 100 kV whenever proposed by automated analysis of the localizer. An additional small scan aligned to the jaw was performed at a fixed 120 kV setting. Image quality was assessed by two radiologists on a standardized Likert-scale and measurements of signal- (SNR) and contrast-to-noise ratio (CNR). Radiation dose was assessed as CTDI_vol.

Results

Diagnostic image quality was excellent in both groups and did not differ significantly (p?=?0.34). Image noise in the 100 kV data was increased and SNR decreased (17.8/9.6) in the jugular veins and the sternocleidomastoid muscle when compared to 120 kV (SNR 24.4/10.3), but not in fatty tissue and air. However, CNR did not differ statistically significant between 100 (23.5/14.4/9.4) and 120 kV data (24.2/15.3/8.6) while radiation dose was decreased by 7–8 %.

Conclusions

TVA between 100 and 120 kV in combination with TCM led to a radiation dose reduction compared to TCM alone, while keeping CNR constant though maintaining diagnostic image quality.     

Determination of AB-FUBINACA and 5F-NPB-22 in rats exposed to “Bonsai” via inhalation and analysis of seized product

Synthetic cannabinoids (SCs) are the most rapidly growing class of recreational designer drugs. Illicit drug manufacturers began to produce herbal smoking materials under a variety of brands names, e.g. “Spice, K2, Bonsai, Yucatan Fire”. They were appeared on the European market in 2008. In this study, types of SCs in the herbal product sold as “Bonsai” in Turkey were determined and the identification of these substances in biological samples collected from rats depending on the inhalation of different amounts of plant material were aimed.To determine the SC species in the content of the plant product, analysis was performed via gas chromatography-mass spectrometry. Liquid-liquid extraction methods were utilized for blood and organ samples, while solid-phase extraction with β-glucuronidase enzyme treatment was applied for urine sample preparation. The relationship between the amount of burned plant and the amount of SCs accumulated in the blood, urine and organ samples of rats exposed to the plant product by inhalation was examined by liquid chromatography-tandem mass spectrometry.AB-FUBINACA and 5F-NPB-22 were detected in the herbal product. A significant correlation was found between the amount of herbal product inhaled and the prevalence of SCs, especially in lung tissues while no SCs were detected in the blood and urine samples of rats.There is currently no study on biological samples of individuals exposed to herbal products containing SCs by inhalation. Regarding the findings obtained in this study, the overall increase in the amounts of herbal product inhaled was demonstrated to pose a potential risk to humans.     

Treatment of malnutrition decreases complication rates and shortens the length of hospital stays in a radiation oncology department

Purpose

The nutritional status of inpatients influences the therapeutic outcome. Malnutrition is a common comorbidity in oncological patients. Both radio- and radiochemotherapy may contribute to the additional deterioration of the nutritional status. The aim of this study was to evaluate the impact of specialized treatment of malnutrition as a clinical routine.

Methods

The nutritional status of inpatients was assessed by the Nutritional risk screening (NRS-2002) on the day of admission to the University Department of Radiation Oncology. In case of significantly elevated NRS-2002 (NRS?≥?3), a guideline-compliant, individual nutritional treatment was initiated by a specialized nutrition support team. The influence of the nutritional status and nutritional treatment on length of stay and complication rate was assessed.

Results

Of 840 included patients, 344 patients (40.95%) were at risk for malnutrition. Malnutrition was a significant, independent risk factor for both prolonged hospital stay, represented by the deviation between the actual length of stay and the DRG-associated mean length of stay (dLOS at risk: 0.88 days, dLOS not at risk: ?0.88 days, p?=?0.0047), as well as for the occurrence of complications (OR: 1.758 CI: [1.286–2.402], p?=?0.0006). In the group of 337 (40.12%) rehospitalized patients the nutritional management was able to assimilate the values of length of stay as well as the complication rates to standard values.

Conclusions

The high risk for malnutrition and the negative consequences for patients and hospitals underline the urgent need for malnutrition screening on admission and treatment of malnutrition. A specialized, interdisciplinary nutrition support team positively influences patient outcome and should be established routinely in all oncological disciplines.

     

Assessment of genetic damage in peripheral blood of human volunteers exposed (whole-body) to a 200 μT, 60 Hz magnetic field

Aim:?To investigate the extent of damage in nucleated cells in peripheral blood of healthy human volunteers exposed to a whole-body 60 Hz, 200 μT magnetic field.

Materials and methods:?In this study, 10 male and 10 female healthy human volunteers received a 4 h whole-body exposure to a 200 μT, 60 Hz magnetic field. In addition, five males and five females were treated in a similar fashion, but were exposed to sham conditions. For each subject, a blood sample was obtained prior to the exposure period and aliquots were used as negative- (pre-exposure) and positive- [1.5 Gray (Gy) ⁶⁰Cobalt (⁶⁰Co) γ-irradiation] controls. At the end of the 4 h exposure period, a second blood sample was obtained. The extent of DNA damage was assessed in peripheral human blood leukocytes from all samples using the alkaline comet assay. To detect possible clastogenic effects, the incidence of micronuclei was assessed in phytohemagglutinin (PHA)-stimulated lymphocytes using the cytokinesis-block micronucleus assay.

Results:?There was no evidence of either increased DNA damage, as indicated by the alkaline comet assay, or increased incidence of micronuclei (MN) in the magnetic field exposed group. However, an in vitro exposure of 1.5 Gy γ-irradiation caused a significant increase in both DNA damage and MN induction.

Conclusions: This study found no evidence that an acute, whole-body exposure to a 200 μT, 60 Hz magnetic field for 4 hours could cause DNA damage in human blood.     

Biological effects and inter-individual variability in peripheral blood lymphocytes of healthy donors exposed to 60 MeV proton radiotherapeutic beam

Purpose: The aim of our study was to investigate the amount of initial DNA damage and cellular repair capacity of human peripheral blood lymphocytes exposed to the therapeutic proton beam and compare it to X-rays.

Materials and methods: Lymphocytes from 10 healthy donors were irradiated in the Spread Out Bragg Peak of the 60?MeV proton beam or, as a reference, exposed to 250?kV X-rays. DNA damage level was assessed using the alkaline version of the comet assay method. For both sources of radiation, dose–DNA damage response (0–4?Gy) and DNA repair kinetics (0–120?min) were estimated. The observed DNA damage was then used to calculate the relative biological effectiveness (RBE) of the proton beam in comparison to that of X-rays.

Results: Dose–response relationships for the DNA damage level showed linear dependence for both proton beam and X-rays (R²?=?0.995 for protons and R²?=?0.993 for X-rays). Within the dose range of 1–4?Gy, protons were significantly more effective in inducing DNA damage than were X-rays (p?<?.05). The average RBE, calculated from the proton and X-ray doses required for the iso-effective, internally standardized tail DNA parameter (sT-DNA) was 1.28?±?0.57. Similar half-life time of residual damage and repair efficiency of induced DNA damage for both radiation types were observed. In the X-irradiated group, significant inter-individual differences were observed.

Conclusions: Proton therapy was more effective at high radiation doses. However, DNA damage repair mechanism after proton irradiation seems to differ from that following X-rays.