Evaluation of the effects of simulated hypoxia by CoCl2 on radioresistance and change of hypoxia-inducible factors in human glioblastoma U87 tumor cell line.

PURPOSE: Glioblastoma (GBM) is considered the most common and lethal type of brain tumor with a poor prognosis. GBM treatment has challenges due to its aggressive nature, which often causes treatment failure and recurrence. Hypoxia is one of the characteristics of glioblastoma tumors that contribute to radioresistance and malignant phenotypes of GBM. In this study, we aimed to determine the effects of hypoxia on the radiosensitivity of U87 GBM cells by the hypoxia-mimicking model. METHODS: Following the treatment of cells with different concentrations of CoCl2, an MTT assay was used to evaluate the cytotoxicity of CoCl2. To understand the effects of Ionizing radiation on CoCl2-treated groups, cells were exposed to irradiation after pretreating with 100 µM CoCl2, and a clonogenic survival assay was performed to determine the radiosensitivity of U87 cells. Also, the intracellular Reactive oxygen level was measured by 2',7'-dichlorofluorescein diacetate (DCFDA) probe staining. Additionally, the expression of hypoxia-associated genes, including HIF-1α, HIF-2α, and their target genes (GLUT-1), was monitored by reverse transcription polymerase chain reaction (RT-PCR). RESULTS: Our study revealed that the cell viability of CoCl2-treated cells was decreased in a concentration-dependent manner. Also, CoCl2 did not cause any cytotoxicity on U87 cells at a concentration of 100 µM after treatment for 24 h. Colony formation assay showed that CoCl2 pretreatment induced radioresistance of tumor cells compared to non-treated cells. Also, CoCl2 can protect cells against irradiation by the clearance of ROS. Moreover, Real-time results showed that the mRNA expression of HIF-1α and GLUT-1 were significantly upregulated following hypoxia induction and/or irradiation condition. However, the level of HIF-2α mRNA did not change significantly in hypoxia or irradiation alone conditions, but it increased significantly only in hypoxia + irradiation conditions. CONCLUSION: Taken together, our results indicated that simulating hypoxia by CoCl2 can effectively increase hypoxia-associated genes, specially HIF-1α and GLUT-1, but did not affect HIF-2α gene expression. Also, it can increase the clearance of ROS, respectively, and it leads to inducing radioresistance of U87 cells.

Chromosomal Instability in Various Generations of Human Mesenchymal Stem Cells Following the Therapeutic Radiation.

Background: Radiotherapy is a crucial treatment for most malignancies. However, it can cause several side effects, including the development of secondary malignancies due to radiation-induced genomic instability (RIGI). The aim of this study was to evaluate genomic instability in human mesenchymal stem cells (hMSCs) at different X-ray radiation doses. Additionally, the study aimed to examine the relative expression of certain genes involved in DNA repair, proto-oncogenes, and tumor suppressor genes. Methods: After extracting, characterizing, and expanding hMSCs, they were exposed to X-ray beams at doses of 0, 0.5, 2, and 6 Gy. Nuclear alterations were evaluated through the cytokinesis-block micronucleus (CBMN) assay at 2, 10, and 15 days postirradiation. The expressions of BRCA1, BRCA2, TP53, Bax, Bcl2, and KRAS genes were analyzed 48 hr after irradiation to evaluate genomic responses to different radiation doses. Results: The mean incidence of micronuclei, nucleoplasmic bridges, and nuclear buds was 4.8 ± 1.6, 47.6 ± 6, and 18 ± 2.6, respectively, in the nonirradiated group 48 hr after the fourth passage, per 1,000 binucleated cells. The incidence of micronuclei in groups exposed to 0.5, 2, and 6 Gy of radiation was 14.3 ± 4.9, 32.3 ± 6.5, and 55 ± 9.1, respectively, 48 hr after irradiation. The expression levels of the BRCA2, Bax, TP53, and KRAS genes significantly increased after exposure to 6 Gy radiation compared to the control groups. However, there was no significant increase in BRCA1 and Bcl2 gene expression in our study. Conclusion: This study demonstrated significant nuclear alterations in the 10 days postirradiation due to the RIGIs that they inherited from their irradiated ancestral cells. While chromosomal instability is a prevalent event in malignant cells, so it seems necessary to optimize radiotherapy treatment protocols for tissues that contain stem cells, especially with IMRT, which delivers a low dose to a larger volume of tissues.

Establishment and validation of a calibration curve for dicentric chromosome induced by 6MV X-ray.

Radiation during radiotherapy and nuclear accidents is currently one of the biggest concerns for the international community. Biological dosimetry examines the amount of damage caused by radiation at the cellular level by quantifying a radiation biomarker. In particular, the dicentric chromosome assay is a biodosimetric technique that can quantify radiation damage by correlating radiation dose exposure with the frequency of dicentric chromosomes in the peripheral lymphocytes extracted from exposed individuals. This study aims to present of the reference dose-response calibration curve for biodosimetry laboratory of Mashhad University of Medical Sciences (north-east of Iran). In all, 40 samples of peripheral blood from four healthy volunteers were irradiated at doses of 0-5 Gray in a customised water phantom using a 6 MV X-rays at dose rate of 2 Gy/min from a linear accelerator. The irradiated samples were cultured and analysed according to the International Atomic Energy Agency Cytogenetic Dosimetry Protocol (2011) with some modifications. Linear-quadratic model curve fitting and further statistical analysis were done using Chromosome Aberration Calculation Software Version 2.0 and Dose Estimate (Version 5.2). The curve equation obtained was ${Y}_{dic}=0.0533{D}^2+0.0231D+0.0001$ and was in the range of other studies. Validation of the calibration curve was done by estimating the dose of blind samples.

Inducing apoptosis by using microRNA in radio-resistant prostate cancer: an in-silico study with an in-vitro validation.

BACKGROUND: One of the problems with radiation therapy (RT) is that prostate tumor cells are often radio-resistant, which results in treatment failure. This study aimed to determine the procedure involved in radio-resistant prostate cancer apoptosis. For a deeper insight, we devoted a novel bioinformatics approach to analyze the targeting between microRNAs and radio-resistant prostate cancer genes. METHOD: This study uses the Tarbase, and the Mirtarbase databases as validated experimental databases and mirDIP as a predicted database to identify microRNAs that target radio-resistant anti-apoptotic genes. These genes are used to construct the radio-resistant prostate cancer genes network using the online tool STRING. The validation of causing apoptosis by using microRNA was confirmed with flow cytometry of Annexin V. RESULTS: The anti-apoptotic gene of radio-resistant prostate cancer included BCL-2, MCL1, XIAP, STAT3, NOTCH1, REL, REL B, BIRC3, and AKT1 genes. These genes were identified as anti-apoptotic genes for radio-resistant prostate cancer. The crucial microRNA that knockdown all of these genes was hsa-miR-7-5p. The highest rate of apoptotic cells in a cell transfected with hsa-miR-7-5p was (32.90 ± 1.49), plenti III (21.99 ± 3.72), and the control group (5.08 ± 0.88) in 0 Gy (P < 0.001); also, this rate was in miR-7-5p (47.01 ± 2.48), plenti III (33.79 ± 3.40), and the control group (16.98 ± 3.11) (P < 0.001) for 4 Gy. CONCLUSION: The use of this new treatment such as gene therapy to suppress genes involved in apoptosis can help to improve the treatment results and increase the quality of life of patients with prostate cancer.

Alteration in Expression of Trim29, TRIM37, TRIM44, and ß-Catenin Genes After Irradiation in Human Cells with Different Radiosensitivity.

Introduction: Radiotherapy is a crucial component of treatment for ∼70% of all cancer patients. The identification of effective biomarkers of radiosensitivity (RS) is a fundamental goal of radiobiology. The authors hypothesize that the RS of human normal and tumoral cells is correlated by the level of expression of TRIM29, TRIM37, TRIM44, and ß-catenin genes. Materials and Methods: Clonogenic assay was performed and RS of four cell lines was determined by survival fraction at 2 Gy. To determine the level of gene expression 6 and 24 h after irradiation, RNA was extracted from each cell line, and expression of the above-mentioned genes in cell lines with different RS was determined by real-time polymerase chain reaction (PCR). Results: The clonogenic assay showed that human dermal fibroblasts (fibroblast) and HT-29 (colorectal) cells are radioresistant, while human foreskin fibroblasts (fibroblast) and QU-DB (lung) cells are radiosensitive. Analysis of the real-time PCR data, 6 h after irradiation, showed that the increase and decrease of the expression of TRIM29 and TRIM37 genes were directly correlated with the RS of normal and tumor cells. At 24 h postirradiation, a considerable difference was only observed in the expression of the ß-catenin gene. Conclusion: This study showed that the TRIM29 and TRIM37 genes are involved in the cell response to radiation and proposed that these genes may be biomarkers for predicting RS in normal and tumoral cell lines.

The role of microRNA-induced apoptosis in diverse radioresistant cancers.

Resistance to cancer radiotherapy is one of the biggest concerns for success in treating and preventing recurrent disease. Malignant tumors may develop when they block genetic mutations associated with apoptosis or abnormal expression of apoptosis; Tumor treatment may induce the expression of apoptosis-related genes to promote tumor cell apoptosis. MicroRNAs have been shown to contribute to forecasting prognosis, distinguishing between cancer subtypes, and affecting treatment outcomes in cancer. Constraining these miRNAs may be an attractive treatment strategy to help overcome radiation resistance. The delivery of these future treatments is still challenging due to the excess downstream targets that each miRNA can control. Understanding the role of miRNAs brings us one step closer to attaining patient treatment and improving patient outcomes. This review summarized the current information on the role of microRNA-induced apoptosis in determining the radiosensitivity of various cancers.

Flow cytometric assessment of DNA double-strand break and repair kinetics in prediction of intrinsic radiosensitivity.

Objectives: To enhance the efficiency of radiotherapy (RT), implementation of individual-based treatment is essential. In this way, determining individual intrinsic radiosensitivity (IRS) can be useful to achieve minimal adverse effects of RT. The present study aimed to identify IRS of breast cancer (BC) patients through determination of radiation-induced DNA double-strand breaks (DSBs), repair kinetics, and acute normal tissue complications induced by RT. Materials and Methods: DSBs induction and its repair kinetics in 50 BC patients' lymphocytes were analyzed by flow cytometric analysis of H2AX Ser-139 phosphorylation at 30 min, 3 and 24 hr after in vitro irradiation. In vivo skin dosimetry was done by GAFChromic films and acute skin toxicity was scored by radiation oncologists according to the criteria of Radiation Therapy and Oncology Group (RTOG) in all patients with similar prescribed treatment. Results: The average surface dose for patients ranged from 0.92 to 1.9 Gy and correlation analysis showed no significant relationship with weekly acute skin reactions. Formation of γH2AX after 30 min, slope of dose-response curve and repair kinetics of DSBs after 3 and 24 hr (intrinsic radiosensitivity) were significantly correlated with the RTOG scores following irradiation (clinical radiosensitivity) (r=0.48 and P-value<0.0001, r=0.72 and P-value<0.0001, r=0.48 and P-value<0.001, and finally r=0.53 and P-value<0.001, respectively; (using Pearson's correlation test). Conclusion: Flow cytometric analysis of DNA DSBs by γH2AX measurement has the potential to be developed into a clinical predictor for identifying the overreactor patients prior to RT. Our result suggests that the slope-related quantity based on the linear pattern of the dose-response curve has the merit to predict overreactor patients with a sensitivity of 89% and a specificity of 94%.

DNA double-strand break repair and adaptive responses of low-dose radiation in normal and tumor lung cell lines.

The adaptive response (AR), which can be induced by low-dose ionizing radiation (LD), may influence the therapeutic ratio of cancer treatment. We investigated the AR and the DNA double-strand break (DSB) repair pathway in human lung tumor cells and normal cells. We measured viability and proliferation of normal lung cells (MRC-5) and lung cancer cells (QU-DB) using the MTT and colony formation assays. Flow cytometric analysis of γ-H2AX was used to measure DNA-DSBs induction, repair, and residual damages. AR was seen in the normal cells but not in the cancer cells. Our findings suggest that LD stimulates DSB repair and that this may contribute to distinctive AR in normal vs. cancer cells.

Skin Dosimetry with EBT3 Radiochromic Film in Radiotherapy of Parotid Cancer.

BACKGROUND: Skin is a sensitive organ and should be spared in radiotherapy and irradiation of skin in radiotherapy can cause to acute and late skin effects such as erythema, desquamation, epilation, color change, or even necrosis. OBJECTIVE: The aim of the present study is to do skin dosimetry in radiotherapy of parotid cancer using Gafchromic EBT3 radiochromic film. EBT3 radiochromic films were calibrated in 0.2-5 Gy dose range. MATERIAL AND METHODS: This is an experimental study in the field of radiotherapy physics. Treatment planning was performed on a RANDO phantom for treatment of parotid cancer by a clinical oncologist. Based on the treatment planning, the skin dose at various points in the overlapping region of right anterior-oblique and right posterior-oblique fields were measured using EBT3 radiochromic film. RESULTS: The minimum and maximum skin doses in a fraction (with 2.0 Gy prescribed dose) were 0.50 Gy and 0.97 Gy, respectively. Based on these values, the total skin dose in 30 treatment fractions (for removed tumor) or in 35 treatment fractions (for unremoved tumor) was in the range of 15-33 Gy. CONCLUSION: Based on the skin dosimetry results of parotid cancer radiotherapy using EBT3 films, it is predicted that there will occur mild skin reactions and these reactions can be neglected due to being mild.

Geant4 Modeling of Cellular Dosimetry of 188Re: Comparison between Geant4 Predicted Surviving Fraction and Experimentally Surviving Fraction Determined by MTT Assay.

BACKGROUND: The importance of cellular dosimetry in both diagnostic and radiation therapy is becoming increasingly recognized. OBJECTIVE: This study aims to compare surviving fractions, which were predicted using Geant4 and contained three types of cancer cell lines exposed to 188Re with the experimentally surviving fraction determined by MTT assay. MATERIAL AND METHODS: In this comparative study, Geant4 was used to simulate the transport of electrons emitted by 188Re from the cell surface, cytoplasm, nucleus or medium around the cells. The nucleus dose per decay (S-value) was computed for models of single cell and random monolayer cell. Geant4-computed survival fraction (SF) of cancer cells exposed to 188Re was compared with the experimental SF values of MTT assay. RESULTS: For single cell model, Geant4 S-values of nucleus-to-nucleus were consistent with values reported by Goddu et al. (ratio of S-values by analytical techniques vs. Geant4 = 0.811-0.975). Geant4 S-values of cytoplasm and cell surface to nucleus were relatively comparable to the reported values (ratio =0.914-1.21). For monolayer model, the values of SCy→N and SCS→N, were greater compared to those for model of single cell (2%-25% and 4%-38% were larger than single cell, respectively). The Geant4 predicted SF for monolayer MCF7, HeLa and A549 cells was in agreement with the experimental data in 10µCi activity (relative error of 2.29%, 2.69% and 2.99%, respectively). CONCLUSION: Geant4 simulation with monolayer cell model showed the highest accuracy in predicting the SF of cancer cells exposed to homogeneous distribution of 188Re in the medium.

Radiation-induced DNA damage and altered expression of p21, cyclin D1 and Mre11 genes in human fibroblast cell lines with different radiosensitivity.

PURPOSE: Radiotherapy plays a pivotal role in the treatment of cancer. One of the main challenges in this treatment modality is radiation-induced complications in some patients affected by high radiosensitivity (RS). The differences in RS are determined mainly by genetic factors. Therefore, identifying the genes and mechanisms that affect RS in different cells is essential for evaluating radiotherapy outcomes. In the present study, the ability to repair DNA double-stranded breaks (DSB) is evaluated, followed by examining the expression levels of CDKN1A (p21), cyclinD1, and Mre11 genes in human fibroblasts with different RSs. MATERIALS & METHODS: Cellular RS was measured by survival fraction at 2 Gy (SF2). The γ-H2AX assay was used for assessing DNA repair capacity. Eventually, gene expression levels from each cell line 4 and 24 h after irradiation (at 2, 4, and 8 Gy) were measured by real-time PCR. RESULTS: The SF2 values for the cell lines ranged from 0.286 to 0.641, and RS differences of fibroblast cells were identified. Among the studied genes, the expression of Mre11 was the most important. Analysis of the real-time PCR data showed that changes in Mre11 gene expression (4 h after 8 Gy irradiation) were directly correlated with the RS (R2 = 0.905). The difference in the expression of the p21 gene (4 h after 4 Gy irradiation) was also promising. Finally, the flow cytometry analysis showed that the radioresistant cell lines quickly repaired DBS damages. However, the repair process was slow in the radiosensitive cell line, and the residual damage is significantly higher than other cell lines (P < 0.01). CONCLUSIONS: This study indicates that changes in the expression of p21 and Mre11 genes play an important role in cell response to radiation and thus these genes can be introduced as biomarkers to predict RS in normal cell lines.

In vivo study of interferon-γ, transforming growth factor-ß, and interleukin-4 gene expression induced by radioadaptive response.

INTRODUCTION: In the present study, the radioadaptive role of the immune system induced by low dose (LD) was investigated for its in vivo protective activity. MATERIALS AND METHODS: Quantitative analysis of cytokine gene expression was assessed for their in vivo activity in BALB/c mice. To evaluate the adaptive response induced by LD on the mice spleen lymphocyte, the cytokine interleukin (IL)-4, interferon (IFN)-γ, and transforming growth factor (TGF)-ß expression was measured by a real-time quantitative polymerase chain reaction. To verify the radioadaptive effect of LD, animals were preirradiated at 10 cGy from a 60 Co source and then challenge dose at 200 cGy was delivered. Independent sample student's t-test was employed to compare cytokine gene expression in radioadaptive (10 + 200 cGy), LD (10 cGy), high-dose (HD, 200 cGy), and control groups of animals. RESULTS: Following the HD, the cytokine gene expression of IFN-γ, IL-4, and TGF-ß was significantly decreased compared to the control group (P = 0.0001). However, TGF-ß expression was also decreased significantly in the LD and adaptive groups compared to the control group (P = 0.0001). IFN-γ/IL-4 ratio in the adaptive group was significantly decreased compared to the HD group (P = 0.0001). CONCLUSION: These results indicate that the immune system plays an important role for radioadaptive response induction by LD radiation to adjust the harmful effects of HD irradiation.

Assessment of skin dose in breast cancer radiotherapy: on-phantom measurement and Monte Carlo simulation.

AIM: The main purpose of the present study is assessment of skin dose in breast cancer radiotherapy. BACKGROUND: Accurate assessment of skin dose in radiotherapy can provide useful information for clinical considerations. MATERIALS AND METHODS: A RANDO phantom was irradiated using a 6 MV Siemens Primus linac with medial and tangential radiotherapy fields for simulating breast cancer treatment. Dosimetry was also performed on various positions across the fields using an EBT3 radiochromic film. Similar conditions of measurement on the RANDO phantom including field size, irradiation angle, number of fields, etc. were subsequently simulated via the Monte Carlo N-Particle Transport code (MCNP). Ultimately, dose values for corresponding points from both methods were compared. RESULTS: Considering dosimetry using radiochromic films on the RANDO phantom, there were points having underdose and overdose based on the prescribed dose and skin tolerance levels. In this respect, 81.25% and 18.75% of the points had underdose and overdose, respectively. In some cases, several differences were observed between the measurement and the MCNP simulation results associated with skin dose. CONCLUSION: Based on the results of the points which had underdose, it was suggested that a bolus should be used for the given points. With regard to overdose points, it was advocated to consider skin tolerance dose in treatment planning. Differences between the measurement and the MCNP simulation results might be due to voxel size of tally cells in simulations, effect of beam's angle of incidence, validation time of linac's head, lack of electronic equilibrium in the build-up region, as well as MCNP tally type.

PHA stimulation may be useful for FDXR gene expression-based biodosimetry.

OBJECTIVES: Nowadays, ionizing radiation (IR) has a significant contribution to the diagnostic and therapeutic medicine, and following that, health risks to individuals through unexpected exposure is greatly increased. Therefore, biological and molecular technology for estimation of dose (biodosimetry) is taken into consideration. In biodosimetry methods stimulation of cells to proliferation is routine to achieve more sensitivity of techniques. However, this concept has recently been challenged by new molecular methods such as gene expression analysis. This study aims to investigate the stimulation effects on gene expression biodosimetry. MATERIALS AND METHODS: The blood samples were taken from15 patients who were irradiated by TC-99 MIBI, before radiopharmaceutical injection and 24 hr after injection. Lymphocytes were extracted immediately and activated by (phytohemagglutinin) PHA for 24 hr and XPA and FDXR expression levels were investigated by employing relative quantitative Real-Time PCR. RESULTS: The results of this study show a significant increase in the FDXR expression level and a significant decrease in the XPA after stimulation of irradiated lymphocytes. Interestingly, a significant increasing trend in the FDXR expression level (at 0.05 significance level) following cell stimulation to the division was observed. CONCLUSION: Our results suggest that the PHA activation role in gene expression-based biodosimetry is strongly depended on the target genes and the relevant protein pathways. Finally, cell stimulation looks to be useful for some specific genes, such as FDXR, due to the increasing trend in expression and improvement of sensitivity of gene expression-based biodosimetry method.

microRNAs: Potential glioblastoma radiosensitizer by targeting radiation-related molecular pathways.

Glioblastoma (GBM) is the most lethal type of primary brain tumor. Currently, even with optimal and multimodal cancer therapies, the survival rate of GBM patients remains poor. One reason for inadequate response of GBM tumors to radiotherapy is radioresistance (RR). Thus, there is a critical need for new insights about GBM treatment to increase the chance of treatment. microRNAs (miRNAs) are important regulatory molecules that can effectively control GBM radiosensitivity (RS) by affecting radiation-related signal transduction pathways such as apoptosis, proliferation, DNA repair and cell cycle regulation. miRNAs provide new clinical perspectives for developing effective GBM treatments. A growing body of literature has demonstrated that GBM RS can be modified by modulating the expression of miRNAs such as miR-7, miR-10b, miR-124, miR-128, miR-320, miR-21, miR-203, and miR-153. This paper highlights the miRNAs and the underlying molecular mechanisms that are involved in the RS of GBM. Besides highlighting the role of miRNAs in different signaling pathways, we explain the mechanisms that affect RS of GBM for modulating radiation response at the clinical level.

Measurement of fast neutron contamination caused by the presence of wedge and block using CR-39 detector.

OBJECTIVE: Undesired neutron contamination imposed to patients during treatment is among the main factors increasing the risk of secondary cancer in radiotherapy. This additional undesirable dose is due to neutron contamination production in high-energy accelerators. In this study, neutron contamination is investigated in the presence of wedge and block in 15 MV photon fields of Siemens Primus linear accelerator. MATERIALS AND METHODS: Neutron production by 30°, 45°, and 60° wedges and cerrobend block was investigated. Measurements were conducted in a 10 cm × 10 cm field at the source to -surface distance of 100 cm at 0.5, 2, 3, and 4 cm depths of a 30 cm × 30 cm × 30 cm Perspex phantom using the CR-39 passive film detectors. Chemical etching was performed using sodium hydroxide solution with 6.25 M concentration as the etchant at 85°C for 3 h. RESULTS: The neutron dosimetry results reveal that the presence of wedge and block increases the neutron contamination. However, the 45° wedge is most effective in producing neutron contamination. The results also show that the fast neutron contamination is lower in the steeper depths. CONCLUSION: The presence of a wedge in a therapeutic high-energy photon field is a source of neutron contamination and may be of concern regarding clinical aspects. The results of this study show that superficial tissues such as skin will incur higher fast neutron contamination than the deep tissues.

A comparison between skin dose of breast cancer patients at the breast region, measured by thermoluminescent dosimeter in the presence and absence of bolus.

AIM: The aim of this study was to measure entrance skin dose (ESD) on the breast of patients who had undergone radiotherapy following surgery, in the presence and absence of bolus. MATERIALS AND METHODS: In this study, the ESD on the breast of 22 female patients was measured using thermoluminescent dosimeter-100 chips. For each patient, the ESD was measured 3 times (once without bolus and twice using bolus). The bolus types used in this study include super flab and wax. RESULTS: The average ESDs on the breast of patients (from both medial and lateral tangential fields) in the presence of the super flab bolus and absence of bolus were 225.8 and 148.17 cGy, respectively, that when using the bolus, around 52% increasing in ESD was observed. The results showed a significant relationship between the ESD on the breast of patients and bolus types (P = 0.002); in addition, correlation coefficient between the two boluses (super flab and wax) was 0.615 (r = 0.615). CONCLUSION: When using the bolus in postmastectomy irradiation, it is noted that in dose delivery to the chest wall, surgical scar or skin of the treated region should be considered. The use of the bolus as a substance that increases of the skin dose can sometimes cause an excessive increase in skin dose that may cause severe skin reactions and underdosing of underlying tissues. Furthermore, using wax bolus in regions that do not require a lot of shaping of bolus is affordable.

Assessment of accuracy of out-of-field dose calculations by TiGRT treatment planning system in radiotherapy.

AIM: The objective was to quantify the accuracy of dose calculation for out-of-field regions by the commercially available TiGRT version 1.2 (LinaTech, Sunnyvale, CA, USA) treatment planning system (TPS) for a clinical treatment delivered on a Siemens Primus with the single energy of 6 MV. MATERIALS AND METHODS: Two tangential open fields were planned by TiGRT TPS to irradiate the left breast of a RANDO phantom. Dose values to out-of-field points were calculated by TiGRT TPS. A RANDO phantom was then irradiated, and dose values at set points were measured using thermoluminescent detectors-100 (TLDs-100) which were located within the phantom. Finally, the TLD-measured dose was compared to the TPS-calculated dose and the accuracy of TPS calculations at different distances from the field edge was quantified. RESULTS: The measurements showed that TiGRT TPS generally underestimated the dose of out-of-field points and this underestimation worsened for regions relatively close to the treatment field edge. The mean underestimation of out-of-field doses was 39%. Nevertheless, the accuracy of dose calculation by this TPS for most in-field regions was within tolerance. CONCLUSION: This study highlights the limitations of TiGRT TPSs in calculating of the out-of-field dose. It should be noted that out-of-field data for this TPS should only be applied with a certain understanding of the accuracy of calculated dose outside the treatment field. Therefore, using the TPS-calculated dose could lead to an underestimation of secondary cancer risk as well as a weak clinical decision for patients with implantable cardiac pacemakers or pregnant patients.

In vivo Exposure Effects of 99mTc-methoxyisobutylisonitrile on the FDXR and XPA Genes Expression in Human Peripheral Blood Lymphocytes.

OBJECTIVES: In recent years, the application of radiopharmaceuticals in nuclear medicine has increased substantially. Following the diagnostic procedures performed in nuclear medicine departments, such as myocardial perfusion imaging, patients generally receive considerable doses of radiation. Normally, radiation-induced DNA damages are expected following exposure to a low-dose ionizing radiation. In order to detect molecular changes, high-sensitivity techniques must be utilized. The aim of this study was to assess the effect of a low-dose (below 10 mSv) gamma ray on gene expression using quantitative real-time polymerase chain reaction (qRT-PCR). METHODS: Blood samples were obtained from 20 volunteer patients who underwent myocardial perfusion imaging. They were given various doses of Technetium-99m methoxyisobutylisonitrile (99mTc-MIBI). After that, peripheral blood mononuclear cells (PBMNs) were derived, and then total RNA was extracted and reverse-transcribed to cDNA. Finally, the expression levels of xeroderma pigmentosum complementation group-A (XPA) and ferredoxin reductase (FDXR) genes were determinded through qRT-PCR technique using SYBR Green. RESULTS: XPA and FDXR expression levels were obtained following a very low-dose ionizing radiation. A significant up-regulation of both genes was observed, and the gene expression level of each individual patient was different. If differences in the administered activity and radiosensitivity are taken into account, the observed differences could be justified. Furthermore, gender and age did not play a significant role in the expression levels of the genes under study. CONCLUSION: The up-regulation of FDXR after irradiation revealed the high-sensitivity level of this gene; therefore, it could be used as an appropriate biomarker for biological dosimetry. On the other hand, the up-regulation of XPA is an indication of DNA repair following radiation exposure. According to linear no-threshold model (LNT) and the results obtained from this study, a very low dose of ionizing radiation could bring about adverse biological effects at molecular level in the irradiated person.