C. Kappas

Survivin regulation by HER2 through NF-κB and c-myc in irradiated breast cancer cells

Radiotherapy is an important treatment modality against cancer resulting in apoptosis and inhibition of cell growth. Survivin is an important cancer biomarker conferring to tumour cells increased survival potential by inhibiting apoptosis. In the present study, we investigated the implication of breast cancer cells features, as hormone receptors and p53 status, in the radio‐resistance of breast cancer cells and in the regulation of survivin’s expression by nuclear factor (NF)‐κB and c‐myc. Six breast cancer cell lines Michigan Cancer Foundation (MCF‐7), MCF‐7/Human Epidermal Growth Factor Receptor (HER)2, M. D. Anderson – Metastatic Breast (MDA‐MB‐231), SK‐BR‐3, BT‐474 and Human Breast Lactating (HBL‐100) were irradiated and cell viability as well as cell cycle distribution were evaluated by 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay and flow cytometry, respectively. Survivin mRNA and protein levels were evaluated by real time PCR and Western blot analysis. Survivin and HER2 gene knockdown was performed with siRNA technology and investigation of transcription factors binding to survivin and c‐myc gene promoters was assessed by chromatin immunoprecipitation. Student’s t‐test and F‐statistics were used for statistical evaluation. Our results demonstrated that only HER2+ breast cancer cells up‐regulated survivin upon irradiation, whereas HER2 knockdown in HER2+ cells led to survivin’s down‐regulation. Survivin and especially HER2 knockdown abolished the observed G2/M cell cycle checkpoint and reduced the radio‐resistance of HER2 overexpressing breast cancer cells. Additionally, HER2 was found to regulate survivin’s expression through NF‐κB and c‐myc transcription factors. This study revealed the significance of HER2 in the radio‐resistance of HER2+ breast cancer cells through induction of transcription factors NF‐κB and c‐myc, leading to activation of survivin, a downstream target oncogene preventing apoptosis.

Correlation between radiation-induced telomerase activity and human telomerase reverse transcriptase mRNA expression in HeLa cells

Purpose: To quantify and correlate human telomerase reverse transcriptase (hTERT) mRNA expression with telomerase activity (TA) after ionizing irradiation of HeLa cells. Materials and methods: TA and hTERT mRNA expression were evaluated, at 24-h intervals, in HeLa cells cultured for up to 144 h, before and after treatment with increasing doses of 6 MV photon ionizing radiation (5 – 20 Gy), using the telomeric repeat amplification protocol (TRAP) assay and real-time reverse transcriptase polymerase chain reaction (RT-PCR), respectively. Cell viability was determined using the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. A prototype phantom was constructed for accurate irradiation of HeLa cells. Results: Treated cells showed a decrease in viability with increasing radiation dose, and a correlation was observed with post-treatment period. TA and hTERT mRNA expression of HeLa cells increased for the first 24 h after irradiation. The maximal increases were approximately two times the un-irradiated cell levels at 24 h post-irradiation, followed by a decrease and a return to the control levels 72 h post-irradiation. The time-course of telomerase activation after 24 h, differed among radiation doses. A dose-dependent G2/M arrest was observed 24 h post-irradiation, along with an increase in polyploidy 48 h post-irradiation and afterwards. Conclusion: A correlation between TA and hTERT mRNA expression and a radiation induced cell cycle dependent modification of hTERT mRNA expression was established for the first 24 h post-irradiation.

On the use of published radiobiological parameters and the evaluation of NTCP models regarding lung pneumonitis in clinical breast radiotherapy

In this study we sought to evaluate and accent the importance of radiobiological parameter selection and implementation to the normal tissue complication probability (NTCP) models. The relative seriality (RS) and the Lyman–Kutcher–Burman (LKB) models were studied. For each model, a minimum and maximum set of radiobiological parameter sets was selected from the overall published sets applied in literature and a theoretical mean parameter set was computed. In order to investigate the potential model weaknesses in NTCP estimation and to point out the correct use of model parameters, these sets were used as input to the RS and the LKB model, estimating radiation induced complications for a group of 36 breast cancer patients treated with radiotherapy. The clinical endpoint examined was Radiation Pneumonitis. Each model was represented by a certain dose–response range when the selected parameter sets were applied. Comparing the models with their ranges, a large area of coincidence was revealed. If the parameter uncertainties (standard deviation) are included in the models, their area of coincidence might be enlarged, constraining even greater their predictive ability. The selection of the proper radiobiological parameter set for a given clinical endpoint is crucial. Published parameter values are not definite but should be accompanied by uncertainties, and one should be very careful when applying them to the NTCP models. Correct selection and proper implementation of published parameters provides a quite accurate fit of the NTCP models to the considered endpoint.

In vivo dosimetry during DSA of the carotid and renal arteries. Deriviation of local DRLs.

The Euratom directive 97/43 recommends the use of patient dose surveys in diagnostic radiology and the establishment of diagnostic reference dose levels (DRLs). The aims of this study are to perform measurements of the entrance surface dose (ESD) during diagnostic digital subtraction angiography (DSA) of the renal and carotid arteries using thermoluminescence dosemeters (TLDs), extraction of local DRLs, and calculation of the effective dose. Dose measurement for the staff was also performed. Dose measurements were performed on 48 participating patients. The mean effective dose was calculated to be 15.9 mSv and 8.9 mSv, for the renal and carotid DSA, respectively. The effective dose of the radiologist was calculated to be 0.022 mSv and 0.023 mSv per procedure for renal and carotid DSA respectively, when wearing a protective apron and using a movable ceiling mounted shield. Radiation dose variation depends on the physical characteristics of the patient, on the procedure preferences by radiologists and on the difficulties in conducting the procedures. The lack of DRLs for the specific examinations lead the research team to choose the DRL for DSA of the renal arteries to be 169 mGy for ESD at the pelvic region and for DSA of the carotid arteries to be 313 mGy for ESD at the region of the aortic arc.

The electromagnetic environment of Magnetic Resonance Imaging systems. Occupational exposure assessment reveals RF harmonics

Magnetic Resonance Imaging (MRI) systems played a crucial role in the postponement of the former occupational electromagnetic fields (EMF) European Directive (2004/40/EC) and in the formation of the latest exposure limits adopted in the new one (2013/35/EU). Moreover, the complex MRI environment will be finally excluded from the implementation of the new occupational limits, leading to an increased demand for Occupational Health and Safety (OHS) surveillance. The gradient function of MRI systems and the application of the RF excitation frequency result in low and high frequency exposures, respectively. This electromagnetic field exposure, in combination with the increased static magnetic field exposure, makes the MRI environment a unique case of combined EMF exposure. The electromagnetic field levels in close proximity of different MRI systems have been assessed at various frequencies. Quality Assurance (QA) & safety issues were also faced. Preliminary results show initial compliance with the forthcoming limits in each different frequency band, but also revealed peculiar RF harmonic components, of no safety concern, to the whole range detected (20-1000MHz). Further work is needed in order to clarify their origin and characteristics.

Radiation doses to patients undergoing enteroclysis

Enteroclysis is a minimally invasive radiographic examination of the small intestine. During the procedure, considerable radiation dose is delivered to the patients. This study intends to: (a) evaluate the radiation dose to the patient using thermoluminescent dosemeters (TLDs, according to the protocol used at Radiology Department, University Hospital of Larissa, Greece; (b) estimate the thyroid surface dose (TSD) and doses to some radiosensitive organs located in the irradiation field. A total of 46 patients was examined. Patients were divided into two groups according to the digital X-ray machine used. The mean entrance surface dose (ESD) was 601.2 ± 96.2 mGy and the mean fluoroscopy time was 8.5 ± 3 min, while the mean TSD was 0.34 ± 0.6 mGy. The ESD for group A was lower by 20 % than group B due to fluoroscopic mode used. The dose values were higher than those in the literature. A local diagnostic reference level was introduced for further patient dose optimisation.

Prospective PET image quality gain calculation method by optimizing detector parameters.

BackgroundLutetium-based scintillators with high-performance electronics introduced time-of-flight (TOF) reconstruction in the clinical setting. Let G′ be the total signal to noise ratio gain in a reconstructed image using the TOF kernel compared with conventional reconstruction modes. G′ is then the product of G1 gain arising from the reconstruction process itself and (n−1) other gain factors (G2, G3, … Gn) arising from the inherent properties of the detector. MethodsWe calculated G2 and G3 gains resulting from the optimization of the coincidence and energy window width for prompts and singles, respectively. Both quantitative and image-based validated Monte Carlo models of Lu2SiO5 (LSO) TOF-permitting and Bi4Ge3O12 (BGO) TOF-nonpermitting detectors were used for the calculations. ResultsG2 and G3 values were 1.05 and 1.08 for the BGO detector and G3 was 1.07 for the LSO. A value of almost unity for G2 of the LSO detector indicated a nonsignificant optimization by altering the energy window setting. G′ was found to be ∼1.4 times higher for the TOF-permitting detector after reconstruction and optimization of the coincidence and energy windows. ConclusionThe method described could potentially predict image noise variations by altering detector acquisition parameters. It could also further contribute toward a long-lasting debate related to cost-efficiency issues of TOF scanners versus the non-TOF ones. Some vendors re-engage nowadays to non-TOF product line designs in an effort to reduce crystal costs. Therefore, exploring the limits of image quality gain by altering the parameters of these detectors remains a topical issue.

The Use of Radiobiological Parameters and the Evaluation of NTCP Models. How Do They Affect the Ability to Estimate Radiation Induced Complications

Normal Tissue Complication Probability (NTCP) models currently used, provide a simplified representation of the clinical radiobiology since there are number of radiobiological mechanisms which affect the clinical outcome and are not taken into account by the models. The use of published radiobiological parameter sets in NTCP modeling introduce uncertainties on the dose-response curves due to the fact that each parameter set is accompanied by a certain standard deviation. Therefore, a model is represented by a doseresponse bandwidth creating areas in which different models may coincide. The purpose of the present study is to evaluate the models and parameter sets determining the overlapping areas thus estimating the importance of parameter application.

Proton Magnetic Resonance Spectroscopy at 3T - Evaluation of Metabolic Profile of Human Brain Lesions

Brain MR imaging at 3T has been increasingly used in clinical practice since a great deal of effort has been invested in research into high magnetic fields to overcome the difficulties of successively working with stronger fields. Theoretically the signal to noise ratio (SNR) of a 3T MR scanner will be double that of a 1.5T one which is advantageous for MR spectroscopy as this technique has always required the strongest possible magnetic field strength. However, the relationship between the magnetic field used and the spectra obtained is very complex depended on several other data acquisition parameters not only field strength. Single-voxel at short echo time (TE=35msec) and multivoxel at long echo time (TE=144msec) spectra were recorded for 46 patients with several brain lesions using PRESS pulse sequence. Spectra were compared in terms of resolution as it varies among changes of data acquisition parameters such as NEX (Number of Excitations), NSA (Number of Signals Averaging) and field homogeneity. Spectra exhibited significantly improved resolution as field homogeneity was improved and NEX as well as NSA were increased. MRS metabolic profiles at 3T gave valuable clinical information when differentiating among brain lesions and tumour stages. However, in some cases, differences among tumour grade and lesion type were subtle, rendering tumour classification a difficult issue.