Comparison of radiation-induced bystander effect in QU-DB cells after acute and fractionated irradiation: an in vitro study

Objective: radiation effects induced in non-irradiated cells are termed radiation-induced bystander effects [RIBE]. The present study intends to examine the RIBE response of QU-DB bystander cells to first, second and third radiation fractions and compare their cumulative outcome with an equal, single acute dose

Materials and Methods: this experimental study irradiated three groups of target cells for one, two and three times with [60]Co gamma rays. One hour after irradiation, we transferred their culture media to non-irradiated [bystander] cells. We used the cytokinesis block micronucleus assay to evaluate RIBE response in the bystander cells. The numbers of micronuclei generated in bystander cells were determined

Results: RIBE response to single acute doses increased up to 4 Gy, then decreased, and finally at the 8 Gy dose disappeared. The second and third fractions induced RIBE in bystander cells, except when RIBE reached to the maximum level at the first fraction. We split the 4 Gy acute dose into two fractions, which decreased the RIBE response. However, fractionation of 6 Gy [into two fractions of 3 Gy or three fractions of 2 Gy] had no effect on RIBE response. When we split the 8 Gy acute dose into two fractions we observed RIBE, which had disappeared following the single 8 Gy dose

Conclusion: the impact of dose fractionation on RIBE induced in QU-DB cells depended on the RIBE dose-response relationship. Where RIBE increased proportionally with the dose, fractionation reduced the RIBE response. In contrast, at high doses where RIBE decreased proportionally with the dose, fractionation either did not change RIBE [at 6 Gy] or increased it [at 8 Gy]

Radiation exposure to critical organs in panoramic dental examination

Nowadays, radiography is a necessary procedure in diagnosis and treatment of patients with dental problems. According to the ALARA [as low as reasonably achievable] principle, dentists must take radiographs of sufficient quality at the lowest possible radiation dose to the patients. The assessment of patient dose on panoramic radiography is difficult because of dynamic nature of the imaging process and the narrow width of the x-ray beam. The present work describes an experiment undertaken using thermoluminescence dosimeters [TLD-100] to obtain the absorbed dose in organs and sensitive tissues in head and neck region during panoramic radiography, based on patient measurement. The overall mean entrance surface dose on thyroid, right and left lens of eyes, parotid glands [right and left] and occipital region in panoramic were 38, negligible, negligible, 367, 319 and 262 micro Gy, respectively. The results show that there are differences between patient doses examined by different panoramic systems. There is a tendency for lower organ doses for digital compared with analogue panoramic units

[ assessment of spinal cord dose following radiotherapy of nasopharyngeal cancer by TLD and rando phantom]

Nasopharyngeal carcinoma is one fo the most common malignancies in the head and neck region and radiotherapy is its treatment of choice. In spite of the fact that it is widely used, due to the presence of many sensitive organs or tissues in this region, patients may suffer from a wide range of side effects. One such sensitive tissue is the spinal cord. If the absorbed dose to spinal cord is greater than its tolerance dose, tehnmyelopathy and Lhermitte's sign are not avoidable. The head and neck of a Rando phantom [reference man] was employed as a hypothetical patient suffering from nasopharyngeal carcinoma. The full course of treatment consisted of three phases. At the beginning of every phase, an oncologist used a simulator to delineate the surface of the Rando Phantom for treatment. TLD chips [TLD-100] were employed for dose measurement. TLD chips were inserted in the previously made holes on the surface of selected slices adjacent to second cervical to fourth thoracic vertebra. Absorbed dose by TLDs wee read by a Harshaw 3500 TLD reader. Total measured dose [in Gy] of various parts of spinal cord adjacent to second cercival to fourth thoracic vertebra varied widely and were as follows respectively: 15.24 +/- 1.31, 50.31 +/- 1.06, 46.15 +/- 2.77, 47.48 +/- 1.42, 54.56 +/- 2.6, 48.92 +/- 0.6, 45.1 +/- 0.45. In other words, the range of doses received by different segments of the spinal cord could be a wide as 15.24 to 54.56 Gy. Although the spinal cord was excluded at the end of the first phase, a significant change in the absorbed dose at the end of the first and second phases was not observed. In phase three, the anterior neck field was replaced by a lateral field and the spinal cord absorbed dose was reduced considerably. According tour results, absorbed doses of the spinal cord segments corresponding to the region confined between the third cervical to third thoracic vertebra were more than the 47 Gy recommended tolerance dose value. Therefore, special attention must be paid to protect this sensitive tissue while the treatment is performed. Application of modern techniques such as IMRT, if available, will reduce the unnecessary dose the spinal cord and its consequent biological risks considerably

[Evaluation of dose distribution accuracy in HDR brachytherapy of esophagus cancer based on MRI normoxic polymer gel dosimetry]

The purpose of this work was to study the ability of MRI normoxic polymer gel dosimetry for evaluating the dose distribution in HDR brachytherapy of esophageal cancer at Imam Reza brachytherapy center [Mashahd, Iran]. Initially, 2 liters of normoxic gel [MAGIc] was fabricated and then poured into 12 calibration test tubes and placed in a perspex walled phantom. The gel phantom was irradiated with a brachytherapy remote-afterloader unit using a cobalt-60 brachytherapy source and the test tubes wee irradiated with a range of known doses with a cobalt-60 teletherapy unit. Imaging was performed with a multi-spin-eco protocol and a T2 quantitative technique using a Siemens 1.5 T MRI machine. The MRI images were transferred to a computer and then image processing was performed in the MATLAB environment to extract R2 maps of the irradiated area. In this study and at the reference point, the dose deviation between the gel dosimetry and the calculated data was 4.5%. The distance to agreement [DTA] for dose profiles was 2.7 mm. Also, dose sensitivity of the MAGIC gel dosimeter was 0.693 S-1Gy-1 [R2=0.9376]. In this work, the data obtained from TPS calculations were found in very good agreement with the measured results provided by gel dosimetry. It was evaluated using a comparison of isodoses and dose at the reference point, and dose profile verification. It is also concluded that the gel dosimetry systems have proven to be a useful tool for dosimetry in clinical radiotherapy applications

[Monte Carlo simulation of a linear accelerator and electron beam parameters used in radiotherapy]

In recent decades, several Monte Carlo codes have been introduced for research and medical applications. These methods provide both accurate and detailed calculation of particle transport from linear accelerators. The main drawback of Monte Carlo techniques is the extremely long computing time that is required m order to obtain a dose distribution with good statistical accuracy. In this study, the MCNP-4C Monte Carlo code was used to simulate the electron beams generated by a Neptun 10 PC linear accelerator. The depth dose curves and related parameters to depth dose and beam profiles were calculated for 6, 8 and 10 MeV electron beams with different field sizes and these data were compared with the corresponding measured values. The actual dosimetry was performed by employing a Welhofer-Scanditronix dose scanning system, semiconductor detectors and ionization chambers. The result showed good agreement [better than 2%] between calculated and measured depth doses and lateral dose profiles for all energies in different field sizes. Also good agreements were achieved between calculated and measured related electron beam parameters such E[0], R[q], R[p] and R[50]. The simulated model of the linac developed in this study is capable of computing electron beam data in a water phantom for different field sizes and the resulting data can be used to predict the dose distributions in other complex geometries

[Radiation by Stander effects mechanism]

Radiation Induced Bystander Effect [RIBE] which causes radiation effects in non-irradiated cells has challenged the principle according to which radiation traversal through the nucleus of a cell is necessary for producing biological responses. What is the mechanism of this phenomenon? To have a better understanding of this rather ambiguous concept substantial number of original and reviewed article were carefully examined. Irradiated cells release molecules which can propagate in cell environment and/or transmit through gap junction intercellular communication. These molecules can reach to non-irradiated cells and transmit bystander signals. In many investigations, it has been confirmed that these molecules are growth factors, cytokinesis, nitric oxide and free radicals like reactive oxygen species [ROS]. Transmission of by stander signal to neighboring cells persuades them to produce secondary growth factors which in their turn cause further cell injuries. Some investigators suggest, organelles other than nucleus [mitochondria and cell membrane] are the origin of these signals. There is another opinion which suggests double strand breaks [DSB] are not directly generated in bystander cells, rather they are due to smaller damage like single strand breaks which accumulate and end up to DSB. Although bystander mechanism has not been exactly known, it can be confirmed that multiple mechanisms and various pathways are responsible for this effect. Cell type, radiation type, experimental conditions and end points are identified as the dominant mechanism. Molecules and pathways which are responsible for RIBE also cause systemic responses to other non-irradiation stresses. So RIBE is a kind of systemic stress or innate immune responses, which are performed by cell microenvironment. Irradiated cells and their signals are components of microenvironment for creating bystander effects