Regulation of XPA could play a role in inhibition of radiation-induced bystander effects in QU-DB cells at high doses.

INTRODUCTION: Radiation-induced bystander effects (RIBE) is the radiobiological effects detected in nonirradiated cells that have received signals from neighboring irradiated cells. In some studies, there are observations that RIBE unexpectedly reduces at high doses. In this study, the expression of two selected apoptotic and repair genes and their possible role in the formation of this unexpected reduction is examined. MATERIALS AND METHODS: The QU-DB cells were irradiated with gamma rays of a60 Co teletherapy unit at doses of 2, 4, 6, and 8 Gy. One hour following irradiation, their culture media were transferred to bystander cells to induced RIBE. After 24 h incubation, the RNA of cells was isolated and cDNA synthesized. Expression levels of BAX, XPA, and XPA/BAX ratio were examined by relative quantitative reverse transcription-polymerase chain reaction. RESULTS: In target cells, up-regulation of both genes was observed at all doses. In bystander cells, at the low dose (2 Gy), the expression of BAX was more than XPA; at 4 Gy, the ratio was balanced. A significant correlation was found between the XPA/BAX ratio and the dose, at high doses pattern of gene expression dominated by DNA repair gene. CONCLUSION: Gene expression profile was distinctive in bystander cells compared to target cells. The observed linear increasing of the ratio of XPA/BAX could support the hypothesis that the DNA repair system is stimulated and causes a reduction in RIBE at high doses.

THERMAL AND FAST NEUTRON DOSE EQUIVALENT DISTRIBUTION MEASUREMENT OF 15-MV LINEAR ACCELERATOR USING A CR-39 NUCLEAR TRACK DETECTORS.

The main purpose of this study is to measure the contribution of the thermal and fast neutron dose along the central axis of the 15 MV Elekta Precise linac in a tissue equivalent phantom. In order to achieve this purpose, different points were selected in three field sizes of 5 × 5 cm2, 10 × 10 cm2 and 15 × 15 cm2. Fast and thermal neutrons were measured using CR-39 nuclear track detectors with and without thermal neutron converter of 10B, respectively. According to the results, the fast neutron dose equivalent was decreased as the depth increased (field size 5 × 5, 10 × 10 and 15 × 15 cm2 fall from 0.35 to 0.15, 0.5 to 0.3 and 0.5 to 0.3, respectively). Thermal dose equivalent was increased as the depth increased in the tissue equivalent phantom (field size 5 × 5, 10 × 10 and 15 × 15 cm2 rise from 0.1 to 0.4, 0.4 to 0.8 and 0.4 to 0.9, respectively). In conclusion, at depth <3 cm, most existing neutrons are fast and CR-39 films are sensitive to fast neutrons; therefore, they are more appropriate than thermoluminescent dosemeters in measuring neutron dose equivalent.

Evaluation of electron dose calculations accuracy of a treatment planning system in radiotherapy of breast cancer with photon-electron technique.

AIM: The aim of this study was to assess the accuracy of electron dose calculations of Prowess Panther treatment planning system (TPS) for abutting photon-electron (PE) technique. In this work, we have assessed the accuracy of electron dose calculations in a simulated internal mammary field because this field is irradiated with electron in PE technique. MATERIALS AND METHODS: In this study, regions of in-field, under electron shield, and outside the internal mammary field were evaluated. Thermoluminescent dosimeter (TLD-700) chips were used within RANDO phantom for dose measurement. Prowess Panther TPS was also applied for dose calculation. Finally, confidence limit values were obtained to quantify the TPS electron dose calculation accuracy of an internal mammary field. RESULTS: The results show that for outside of field and under shield regions, Prowess Panther TPS underestimated the dose compared to the measured doses by TLD-700, whereas for in-field regions, the calculated doses by Prowess Panther TPS compared to the measured doses by TLD-700, for some points are overestimated and other points are underestimated. Finally, the confidence limit values were obtained for various regions of the internal mammary field. Confidence limits for in-field, outside of field, and under shield regions were 54.23, 108.19, and 80.51, respectively. CONCLUSIONS: It is concluded that the accuracy of electron dose calculations of Prowess Panther TPS is not adequate for internal mammary field treatment. Therefore, it is recommended that for fields with electron beams Prowess Panther TPS calculations should not be entirely relied upon.

Bax/Bcl-2 expression ratio in prediction of response to breast cancer radiotherapy.

OBJECTIVES: Radiotherapy is one of the most effective modalities of cancer therapy, but clinical responses of individual patients varies considerably. To enhance treatment efficiency it is essential to implement an individual-based treatment. The aim of present study was to identify the mechanism of intrinsic apoptosis pathway on radiosensitivity and normal tissue complications caused by the radiotherapy. MATERIALS AND METHODS: Peripheral blood mononuclear cells from ten breast cancer patients were exposed to 6MV X-rays to deliver 1 and 2 Gy. Expression levels of Bax, Bcl-2, and Bax/Bcl-2 ratio were examined by relative quantitative RT-PCR. All the patients received similar tangential irradiation of the whole breast and conventional fractionation. Skin dosimetry was done by GAFChromic EBT-3 film and clinical radiosensitivity was determined using the acute reactions to radiotherapy of the skin according to Radiation Therapy Oncology Group score. All statistical analyses were performed using GraphPad Prism, version 7.01. RESULTS: In the in-vitro experiment, Bax and Bax/Bcl-2 ratios were significantly increased with 1 and 2 Gy doses (P<0.001 and P<0.0001, respectively). Herein, the notable result was a significant correlation between dose-response curve slope (as an in-vitro radiosensitivity index) and acute skin toxicity score following irradiation (as a clinical radiosensitivity index). There was no significant relationship between skin dose and reactions (P>0.05 for all patients). CONCLUSION: Significant correlation between Bax/Bcl-2 ratio determined before radiation therapy and clinical response in the patients, can be used as a biomarker to identify radiosensitive individuals. However, further studies are required to validate radiation-induced apoptotic biomarkers.

Comparison of the hypothetical (57)Co brachytherapy source with the (192)Ir source.

AIM OF THE STUDY: The (57)Co radioisotope has recently been proposed as a hypothetical brachytherapy source due to its high specific activity, appropriate half-life (272 days) and medium energy photons (114.17 keV on average). In this study, Task Group No. 43 dosimetric parameters were calculated and reported for a hypothetical (57)Co source. MATERIAL AND METHODS: A hypothetical (57)Co source was simulated in MCNPX, consisting of an active cylinder with 3.5 mm length and 0.6 mm radius encapsulated in a stainless steel capsule. Three photon energies were utilized (136 keV [10.68%], 122 keV [85.60%], 14 keV [9.16%]) for the (57)Co source. Air kerma strength, dose rate constant, radial dose function, anisotropy function, and isodose curves for the source were calculated and compared to the corresponding data for a (192)Ir source. RESULTS: The results are presented as tables and figures. Air kerma strength per 1 mCi activity for the (57)Co source was 0.46 cGyh(-1) cm 2 mCi(-1). The dose rate constant for the (57)Co source was determined to be 1.215 cGyh(-1)U(-1). The radial dose function for the (57)Co source has an increasing trend due to multiple scattering of low energy photons. The anisotropy function for the (57)Co source at various distances from the source is more isotropic than the (192)Ir source. CONCLUSIONS: The (57)Co source has advantages over (192)Ir due to its lower energy photons, longer half-life, higher dose rate constant and more isotropic anisotropic function. However, the (192)Ir source has a higher initial air kerma strength and more uniform radial dose function. These properties make (57)Co a suitable source for use in brachytherapy applications.

A comparison of the doses received by normal cranial tissues during different simple model conventional radiotherapeutic approaches to pituitary tumours.

This aim of this study was to compare the doses received by critical cranial organs when three different radiation techniques were used to treat pituitary tumours. Cranial computed tomography scans of a RANDO phantom and 30 patients were used for pituitary macroadenoma radiotherapy treatment planning. For each slice, target volumes and other critical organs were contoured and three techniques were applied: (A) two parallel-opposed lateral fields, (B) two oblique fields (45°) in coronal plane and (C) two parallel-opposed lateral and anterior fields while the head was tilted 45° in the sagittal plane. The doses received by the target volume and the critical organs for each technique were calculated for all patients. Irradiation was repeated three times for each technique. Finally, the doses that reached the organs of interest resulting from these techniques were compared. The dose delivered to the temporal lobes was 105, 9 and 72 % of the prescribed dose using techniques A, B and C, respectively. The dose received by the cochlea was the lowest in technique C (27 % of prescribed dose) compared with techniques A (79 %) and B (48 %). All techniques delivered 100 % of the prescribed dose to the chiasma. Technique A increased the dose to temporal lobes and the cochlea to such an extent that they exceeded the tolerance dose. Technique B spared the temporal lobes better than technique C; however, technique C was preferred since the dose received by the cochlea in this case was the lowest of all techniques. None of the techniques spared the chiasma.

Preliminary results of an attempt to predict over apron occupational exposure of cardiologists from cardiac fluoroscopy procedures based on DAP (dose area product) values.

This study is an effort to propose a mathematical relation between the occupational exposure measured by a dosimeter worn on a lead apron in the chest region of a cardiologist and the dose area product (DAP) recorded by a meter attached to the X-ray tube. We aimed to determine factors by which DAP values attributed to patient exposure could be converted to the over-apron entrance surface air kerma incurred by cardiologists during an angiographic procedure. A Rando phantom representing a patient was exposed by an X-ray tube from 77 pre-defined directions. DAP value for each exposure angle was recorded. Cardiologist exposure was measured by a Radcal ionization chamber 10X5-180 positioned on a second phantom representing the physician. The exposure conversion factor was determined as the quotient of over apron exposure by DAP value. To verify the validity of this method, the over-apron exposure of a cardiologist was measured using the ionization chamber while performing coronary angiography procedures on 45 patients weighing on average 75 ± 5 kg. DAP values for the corresponding procedures were also obtained. Conversion factors obtained from phantom exposure were applied to the patient DAP values to calculate physician exposure. Mathematical analysis of our results leads us to conclude that a linear relationship exists between two sets of data: (a) cardiologist exposure measured directly by Radcal & DAP values recorded by the X-ray machine system (R (2) = 0.88), (b) specialist measured and estimated exposure derived from DAP values (R (2) = 0.91). The results demonstrate that cardiologist occupational exposure can be derived from patient data accurately.

Design and fabrication of the control part of a prototype multileaf collimator system.

Multileaf collimator (MLC) is among the radiation field shaping systems used for conformal radiotherapy and intensity modulation radiation therapy techniques. The MLC system that has been designed and fabricated in this study includes 52 leaves, 52 stepper motors, 2 DC motors, 16 programmable logic controllers (PLCs) and one human machine interface (HMI). This system can be mounted on conventional linear accelerators (linac) as an add-on accessory. The 52 leaves are mounted on two carriages that are moved independently. The leaves sequence acquired from the image processing of computed tomography images is used to arrange leaves. This sequence is saved in a text file. The leaves are arranged by HMI and labVIEW. Using HMI it is possible to test the operation of PLCs and manually enter the numerical values of the leaves edges. An executable file is developed by labVIEW program, which is graphically user interfaced between the operator and the MLC control system. The projected width of each leaf on the isocenter accelerator (usually at 100 cm from the source) is 10 mm. The positioning accuracy of each leaf is approximately 1.4 mm.

MRC5 and QU-DB bystander cells can produce bystander factors and induce radiation bystander effect.

Radiation damages initiated by radiation-induced bystander effect (RIBE) are not limited to the first or immediate neighbors of the irradiated cells, but the effects have been observed in the cells far from the irradiation site. It has been postulated that bystander cells, by producing bystander factors, are actively involved in the propagation of bystander effect in the regions beyond the initial irradiated site. Current study was planned to test the hypothesis. MRC5 and QU-DB cell lines were irradiated, and successive medium transfer technique was performed to induce bystander effects in two bystander cell groups. Conditioned medium extracted from the target cells was transferred to the bystander cells (first bystander cells). After one hour, conditioned medium was substituted by fresh medium. Two hours later, the fresh medium was transferred to a second group of non-irradiated cells (second bystander cells). Micronucleated cells (MC) were counted to quantify damages induced in the first and second bystander cell groups. Radiation effect was observed in the second bystander cells as well as in the first ones. Statistical analyses revealed that the number of MC in second bystander subgroups was significantly more than the corresponding value observed in control groups, but in most cases it was equal to the number of MC observed in the first bystander cells. MRC5 and QU-DB bystander cells can produce and release bystander signals in the culture medium and affect non-irradiated cells. Therefore, they may contribute to the RIBE propagation.

Assessment of skin dose modification caused by application of immobilizing cast in head and neck radiotherapy.

Skin dose assessment for radiotherapy patients is important to ensure that the dose received by skin is not excessive and does not cause skin reactions. Immobilizing casts may have a buildup effect, and can enhance the skin dose. This study has quantified changes to the surface dose as a result of head and neck immobilizing casts. Medtech and Renfu casts were stretched on the head of an Alderson Rando-Phantom. Irradiation was performed using 6 and 15 MV X-rays, and surface dose was measured by thermoluminescence dosimeters. In the case of 15MV photons, immobilizing casts had no effect on the surface dose. However, the mean surface dose increase reached up to 20 % when 6MV X-rays were applied. Radiation incidence angle, thickness, and meshed pattern of the casts affected the quantity of dose enhancement. For vertical beams, the surface dose increase was more than tangential beams, and when doses of the points under different areas of the casts were analysed separately, results showed that only doses of the points under the thick area had been changed. Doses of the points under the thin area and those within the holes were identical to the same points without immobilizing casts. Higher dose which was incurred due to application of immobilizing casts (20 %) would not affect the quality of life and treatment of patients whose head and neck are treated. Therefore, the benefits of head and neck thermoplastic casts are more than their detriments. However, producing thinner casts with larger holes may reduce the dose enhancement effect.

Investigation of the bystander effect in MRC5 cells after acute and fractionated irradiation in vitro.

Radiation-induced bystander effect (RIBE) has been defined as radiation responses observed in nonirradiated cells. It has been the focus of investigators worldwide due to the deleterious effects it induces in nonirradiated cells. The present study was performed to investigate whether acute or fractionated irradiation will evoke a differential bystander response in MRC5 cells. A normal human cell line (MRC5), and a human lung tumor cell line (QU-DB) were exposed to 0, 1, 2, and 4Gy of single acute or fractionated irradiation of equal fractions with a gap of 6 h. The MRC5 cells were supplemented with the media of irradiated cells and their micronucleus frequency was determined. The micronucleus frequency after single and fractionated irradiation did not vary significantly in the MRC5 cells conditioned with autologous or QU-DB cell-irradiated media, except for 4Gy where the frequency of micronucleated cells was lower in those MRC5 cells cultured in the media of QU-DB-exposed with a single dose of 4Gy. Our study demonstrates that the radiation-induced bystander effect was almost similar after single acute and fractionated exposure in MRC5 cells.

An effective hair removal algorithm for dermoscopy images.

BACKGROUND/PURPOSE: Dermoscopy is one of the major imaging modalities used in the diagnosis of pigmented skin lesions. Due to the difficulty and subjectivity of human interpretation, computerized image analysis techniques have become important tools in this research area. Hair removal from skin lesion images is one of the key problems for the precise segmentation and analysis of the skin lesions. In this study, we present a new scheme that automatically detects and removes hairs from dermoscopy images. METHODS: The proposed algorithm includes two steps: firstly, light and dark hairs and ruler marking are segmented through adaptive canny edge detector and refinement by morphological operators. Secondly, the hairs are repaired based on multi-resolution coherence transport inpainting. RESULTS: The algorithm was applied to 50 dermoscopy images. To estimate the accuracy of the proposed hair detection algorithm, quantitative analysis was performed using TDR, FPR, and DA metrics. Moreover, to evaluate the performance of the proposed hair repaired algorithm, three statistical metrics namely entropy, standard deviation, and co-occurrence matrix were used. CONCLUSION: The results demonstrate that the proposed algorithm is highly accurate and able to detect and repair the hair pixels with few errors. In addition, the segmentation veracity of the skin lesion is effectively improved after our proposed hair removal algorithm.

Monte carlo study of the effect of collimator thickness on T-99m source response in single photon emission computed tomography.

In single photon emission computed tomography (SPECT), the collimator is a crucial element of the imaging chain and controls the noise resolution tradeoff of the collected data. The current study is an evaluation of the effects of different thicknesses of a low-energy high-resolution (LEHR) collimator on tomographic spatial resolution in SPECT. In the present study, the SIMIND Monte Carlo program was used to simulate a SPECT equipped with an LEHR collimator. A point source of (99m)Tc and an acrylic cylindrical Jaszczak phantom, with cold spheres and rods, and a human anthropomorphic torso phantom (4D-NCAT phantom) were used. Simulated planar images and reconstructed tomographic images were evaluated both qualitatively and quantitatively. According to the tabulated calculated detector parameters, contribution of Compton scattering, photoelectric reactions, and also peak to Compton (P/C) area in the obtained energy spectrums (from scanning of the sources with 11 collimator thicknesses, ranging from 2.400 to 2.410 cm), we concluded the thickness of 2.405 cm as the proper LEHR parallel hole collimator thickness. The image quality analyses by structural similarity index (SSIM) algorithm and also by visual inspection showed suitable quality images obtained with a collimator thickness of 2.405 cm. There was a suitable quality and also performance parameters' analysis results for the projections and reconstructed images prepared with a 2.405 cm LEHR collimator thickness compared with the other collimator thicknesses.

Application of a color scanner for (60)Co high dose rate brachytherapy dosimetry with EBT radiochromic film.

UNLABELLED: BACKGROUND.: The aim of this study is to evaluate the performance of a color scanner as a radiochromic film reader in two dimensional dosimetry around a high dose rate brachytherapy source. MATERIALS AND METHODS: A Microtek ScanMaker 1000XL film scanner was utilized for the measurement of dose distribution around a high dose rate GZP6 (60)Co brachytherapy source with GafChromic® EBT radiochromic films. In these investigations, the non-uniformity of the film and scanner response, combined, as well as the films sensitivity to scanner's light source was evaluated using multiple samples of films, prior to the source dosimetry. The results of these measurements were compared with the Monte Carlo simulated data using MCNPX code. In addition, isodose curves acquired by radiochromic films and Monte Carlo simulation were compared with those provided by the GZP6 treatment planning system. RESULTS: Scanning of samples of uniformly irradiated films demonstrated approximately 2.85% and 4.97% nonuniformity of the response, respectively in the longitudinal and transverse directions of the film. Our findings have also indicated that the film response is not affected by the exposure to the scanner's light source, particularly in multiple scanning of film. The results of radiochromic film measurements are in good agreement with the Monte Carlo calculations (4%) and the corresponding dose values presented by the GZP6 treatment planning system (5%). CONCLUSIONS: The results of these investigations indicate that the Microtek ScanMaker 1000XL color scanner in conjunction with GafChromic EBT film is a reliable system for dosimetric evaluation of a high dose rate brachytherapy source.

Air kerma strength characterization of a GZP6 Cobalt-60 brachytherapy source.

BACKGROUND: Task group number 40 (TG-40) of the American Association of Physicists in Medicine (AAPM) has recommended calibration of any brachytherapy source before its clinical use. GZP6 afterloading brachytherapy unit is a (60)Co high dose rate (HDR) system recently being used in some of the Iranian radiotherapy centers. AIM: In this study air kerma strength (AKS) of (60)Co source number three of this unit was estimated by Monte Carlo simulation and in air measurements. MATERIALS AND METHODS: Simulation was performed by employing the MCNP-4C Monte Carlo code. Self-absorption of the source core and its capsule were taken into account when calculating air kerma strength. In-air measurements were performed according to the multiple distance method; where a specially designed jig and a 0.6 cm(3) Farmer type ionization chamber were used for the measurements. Monte Carlo simulation, in air measurement and GZP6 treatment planning results were compared for primary air kerma strength (as for November 8th 2005). RESULTS: Monte Carlo calculated and in air measured air kerma strength were respectively equal to 17240.01 µGym(2) h(-1) and 16991.83 µGym(2) h(-1). The value provided by the GZP6 treatment planning system (TPS) was "15355 µGym(2) h(-1)". CONCLUSION: The calculated and measured AKS values are in good agreement. Calculated-TPS and measured-TPS AKS values are also in agreement within the uncertainties related to our calculation, measurements and those certified by the GZP6 manufacturer. Considering the uncertainties, the TPS value for AKS is validated by our calculations and measurements, however, it is incorporated with a large uncertainty.

Monte Carlo dose calculation of GZP6 (60)Co stepping source based on a matrix shift technique.

BACKGROUND: As a routine method for stepping source simulation, a Monte Carlo program is run according to the number of steps and then the summation of dose from each run is taken to obtain total dose distribution. This method is time consuming. AIM: As an alternative method, a matrix shift based technique was applied to simulate a stepping source for brachytherapy. MATERIALS AND METHODS: The stepping source of GZP6 brachytherapy unit was simulated. In a matrix shift method, it is assumed that a radiation source is stationary and instead the data matrix is shifted based on the number of steps. In this study, by running MCNPX program for one point and calculation of the dose matrix using the matrix shift method, the isodose curves for the esophageal cancer tumor lengths of 4 and 6 cm were obtained and compared with the isodose curves obtained by running MCNPX programs in each step position separately (15 and 23 steps for esophageal cancer tumor lengths of 4 and 6 cm, respectively). RESULTS: The difference between the two dose matrixes for the stepping and matrix shift methods based on the average dose differences are 3.85 × 10(-4) Gy and 5.19 × 10(-4) Gy for treatment length of 4 cm and 6 cm, respectively. Dose differences are insignificant and these two methods are equally valid. CONCLUSIONS: The matrix shift method presented in this study can be used for calculation of dose distribution for a brachytherapy stepping source as a quicker tool compared to other routine Monte Carlo based methods.