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Background : There are growing evidences for chromosomal radioadaptive response in human lymphocytes . Highly variable inter- and intra-individual responses have been reported. Some individuals are non-responders and even in some donors the frequency of chromatid aberrations induced by a challenge dose increases by pre-exposure to an adapting dose. It has been proposed that the lack of radioadaptive response is due to transient physiological factors.

Materials and Methods : We found a young healthy donor who exhibited no radioadaptive response in our initial experiments. After a common adapting dose, the donor occasionally showed a highly increased susceptibility to subsequent high-dose irradiation. To assess whether the lack of radioadaptive response and the induction of a synergistic effect are transient responses , we have performed a 3-year follow-up study employing micronuclei in binucleated cells besides chromatid aberrations as biological endpoints. To eliminate the effect of the cell cycle on intrinsic radiosensitivity of a cell, we used the multiple-fixation regimen for analysis of chromosomal aberrations.

Results : This donor showed no adaptive response in any experiment.

Conclusion : Considering the consistent non-responsiveness observed throughout our serial experiments, it may be concluded that the lack of radioadaptive response is not attributed to some transient physiological factors but rather to permanent constitutional traits. Iran. J. Radiat. Res., 2003 1(1): 55 - 61.

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Background: Radioprotective capability of histamine H₂ receptor antagonists have been shown in several in vivo studies mainly using animal models. However, to verify the effectiveness of these agents in clinical applications, studies should be performed on human cells. In the present study radioprotective properties of these agents was examined in vitro on human lymphocytes using metaphase analysis.

Materials and Methods : In vitro metaphase analysis technique was used to test the effects of cimetidine, ranitidine and famotidine on radiation induced clastogenic effects. Lymphocytes in whole peripheral blood were exposed to 3 Gy gamma-rays at a dose rate of 73.7 cGy/min in the presence or absence of various doses of the drugs used in this study. The frequency of chromosomal aberrations were determined after standard metaphase preparations and staining slides in 5% Giemsa.

Results: Results show that radiation produced a high number of chromosomal aberrations in lymphocytes compared to controls (p<0.001). All three drugs used in this study effectively reduced the frequency of chromosomal aberrations at all doses. Famotidine was found to be more effective than the other two drugs.

Conclusion: From the results obtained it can be concluded that H ₂ -receptor antagonists used in this study effectively reduced the clastogenic effects of radiation with a dose reduction factor (DRF) of 1.5-2 in human lymphocytes in vitro. The way in which these drugs reduce the clastogenic effects of radiation might be via radical scavenging mechanism. Iran . J. Radiat. Res. 2003 1(2): 99 – 104.

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Background: Most of our current understanding of the biological effects of exposure to ionising radiation is based on conventional cytogenetic techniques, which enable us to determine the relationship between chromosomal aberration and dose received by radiation workers. However, conventional techniques have numerous limitations and chromosomal aberrations can be easily missed. Since FISH plays an important role in detecting chromosomal changes, this method was used to reassess data derived from previous studies employing conventional techniques.

Materials and Methods: Two groups of radiographers were the subject of a study on conventional chromosomal aberration and fluorescence in situ hybridisation (FISH) for translocation. The first group was chosen following an accidental contamination incident in a nuclear medicine department. The second group was composed of six radiographers working in an X-ray department with a previous record of overdose as recorded by film-badges these workers had been the subjects of a previous chromosomal study. Coded blood samples from 11 radiographers and 11 controls were analysed for chromosomal aberration and by FISH for translocation. 200 metaphases from the peripheral blood lymphocytes per subject were analysed to investigate possible frequencies of chromosome and chromatid type aberration and 2000 metaphases per subject were scored in FISH method.

Results: There was no significant difference between the radiographers and the control groups in conventional analysis also there was no significant difference at the 95% level of confidence in FISH analysis. There was no correlation between levels of translocation and total lifetime doses from occupational (according film-badge and TLD) and/or background irradiation.

Conclusion: The overall conclusion is that the frequency of chromosomal damage in both groups of radiographers did not exceed that of the control group. Iran . J. Radiat. Res., 2004 1(4): 195-198

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Background: Logistic discriminant method was applied to differentiate malignant from benign in a group of patients with proved breast lesions on the basis of ultrasonic parameters.

Materials and Methods: Our database include 273 patients' ultrasonographic pictures consisting of 14 quantitative variables. The measured variables were ultrasound propagation velocity, acoustic impedence and attenuation coefficient at 10 MHz in breast lesions at 20, 25, 30 and 35 º C temperature, physicsl density and age. This database was randomly divided into the estimation of 201 and validation of 72 samples. The estimation samples were used to build the logistic
discriminant model, and validation samples were used to validate the performance. Finally,
important criteria such as sensitivity, specificity, accuracy and area under the receiver operating characteristic curve (ROC) were evaluated.

Results: Our results showed that the logistic discriminant method was able to classify correctly 67 out of 72 cases presented in the validation sample. The results indicate a remarkable
diagnostic accuracy of 93%.

Conclusion: A logistic discriminantor approach is capable of predicting the probability of
malignancy of breast cancer. Features extracted from ultrasonic measurement on ultrasound imaging is used in this approach. Iran . J. Radiat. Res., 2004 2 (1): 27-34

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Background: In radiotherapy, wedge filters are used for optimizing the tumor dose distribution in patients. The attenuation in beam intensity due to the presence of wedge filter is compensated by means of a wedge factor measured at the central axis of the beam. The field size, depth and SSD dependence of wedge factor have been assessed for 9MV radiations of Neptun PC linear accelerator.

Materials and Methods: Wedge factors (WF) at different SSD, field size (FS) and depth (d) in water were measured for 8 steel wedges with different sizes and angles of 15, 30, 45, and 60 degree. Experimental data were obtained using Neptun 10PC, Linac 9MV X-ray machine, a 3D water phantom, dosimeters and an electrometer. To study the effect of field size on WF, the wedge factor was measured for square field sizes from 5 ´ 5 to 20 ´ 20 cm, with 1 cm increment intervals for all wedges and, at the depth of 10 cm, SSD of 100 cm with monitor unit (MU) of 80. Effects of depth on WF were studied by measurement in various depths from 3-19cm for all wedge angles at SSD of 100cm, field size of 10 ´ 10cm and 80 MU irradiation. Effects of SSD on WF were investigated by a variation of SSD from 90-110cm with 5cm increment intervals while the dosimeter was set at depth of 10cm and field size of 10 ´ 10cm were irradiated for 80MU.

Results: Linear dependence of WF with field size and depth of measurements were confirmed with 95% certainty. Shapiro-Wilk test, showed that the residual data of the regression tests have normal distributions (P>0.05). There was also found no linear relationship between WF and SSD (P>0.05).

Conclusion: WF has linear dependence with field size and depth of measurements, but the rate of variations are less than 2.2% per 10cm variation in field size and less than 1.3% per 10 cm variation in depth of measurements, therefore, correction of WF for field size and depth of
treatments in clinical trials is negligible. Iran . J. Radiat. Res., 2004 2 (2): 53-58

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Background: Induction of radioadaptive responses in cells pretreated with a low dose radiation before exposure to a high dose is well documented by many investigators. The aim of this study is to determine the frequency of chromosomal aberration in peripheral blood lymphocytes of patients treated by radioiodine (¹³¹I) for hyperthyroidism, with or without previous thyroid scan with ^99mTc.

Materials and Methods: Venous blood samples were obtained from 35 patients one month after radioiodine therapy and cytogenetically evaluated using analysis of metaphase in two groups. The first group (n = 15, 13 females and 2 males, mean age= 44.7 ±11.5 years and mean weight 74.4±7.9 Kg) received 5 mCi ^99mTc for thyroid scanning 38.6±19.9 days before radioiodine therapy with 10.4 ± 3.4 mCi ¹³¹I. The second group (n = 20, 14 females and 6 males, mean age = 41.0 ± 10.8 years and mean weight = 68.1±9.2 Kg) didn't have history of thyroid scanning. We also studied a control group (n = 29, 11 Females and 8 males, mean age = 33.7±7.4 and mean weight = 70.0±8.8 Kg) who didn't have any history of diagnostic or therapeutic and also occupational exposure.

Results: The mean frequency of total chromosomal aberrations in the first and second groups and controls were 1.46 ±1.55, 1.65 ± 1.62 and 0.93 ± 0.92 respectively. Results also showed that the mean frequency of total chromosome aberration in two groups were higher than controls and significantly higher in patients who had not received ^99mTc compared those who had undertaken thyroid scan before radioiodine therapy (p=0.03).

Conclusion: These findings may indicate the fact that the radiation dose received from ^99mTc could induce resistance to subsequent higher radiation dose of ¹³¹I in peripheral blood lymphocytes and it might be due to cytogenetic radioadaptive response. Iran . J. Radiat. Res., 2004 2 (2): 69-7 4

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Background: Hot lab is a specially designed room in a nuclear medicine hospital where the radiopharmaceuticals are delivered, stored and prepared for dispensing. ⁹⁹Mo/^99mTc-generator is the major source in the hot lab used for various medical imaging. It is important to maintain a standard for hot lab procedures to optimize the patient care and minimize radiation exposure to all nuclear medicine personnel, patients, public, as well as environment.

Materials and Methods: The radiation doses in the hot lab were measured by GM and NaI Detectors for about 12 months. Package surface doses and generator surface doses were also measured. An increase in the counted rate above background was considered for the study. A constant distance was made in every step.

Results: At the receipt date, the ⁹⁹Mo/^99mTc-generator surface dose (450±150 μGy/hr) found to be nearly six times higher than the package surface dose (80±20 μGy/hr). The dose rate at the outer surface of the fume-hood glass found to be 80±15 μGy/hr in the 1^st day of generator
placement, whereas at the 2^nd day it was 70±12 μGy/hr showing a gradual decline in dose rate during 3^rd (50±10 μGy/hr), 4^th (40±9 μGy/hr), 5^th day (30±6 μGy/hr) and 6^th day (25±4 μGy/hr).

Conclusion: In the 1^st day of a generator storing in the hot lab, the dose rate found to be 3-4 times higher than the 6^th days. The dose rate at various places indicated poor performance of the fume-hood glass. The study emphasizes on the need of growing awareness among all the
radiation workers and encouraging the safe working practices in nuclear medicine. Iran . J. Radiat. Res., 2004 2 (2): 75-78

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Background: Lymphocyte-dicentric assay is the most generally accepted method for biological dosimetry of overexposed individuals. In this study, the frequency of unstable chromosome
aberration in blood lymphocytes was used to estimate radiation dose received by individuals. Evaluation of dose using a calibration curve produced elsewhere may have a significant uncertainty therefore, experiments were performed to produce a dose-response curve using an
established protocol of international atomic energy agency.

Materials and Methods: Lymphocytes in whole peripheral blood obtained from healthy
individuals, were exposed to various doses of gamma radiation (0.25 – 4 Gy). Then after 1 hour of incubation in 37 ^oC, were cultured in complete RPMI-1640 medium. 500 mitoses were
analysed for the presence or absence of unstable chromosomal aberrations for each radiation dose after the standard metaphase preparation and staining slides.

Results and Conclusion: Intercellular distribution of dicentric chromosomes at each radiation dose has been used to contrast a dose-response curve. It seems that dose-effect relationship
follows with the linear-quadratic model. There is a good agreement between our dose-response curves with similar published studies by other laboratories. Iran . J. Radiat. Res., 2004 2 (2): 85-8 8

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Background: A set of hardware stereotactic radiosurgery is designed and constructed. The scope of this article is to describe how we have designed and developed stereotactic collimation assembly for a 9 MV Neptun 10 PC linac.

Materials and methods: One collimator holder and six collimators were made, with their
radiation field diameter between 12.5 mm to 25 mm at isocenter level. Beam data, such as depth dose percent, off axis ratio and output factor of the collimators were measured. Isocentric
accuracy and dose delivery, accuracy tests were also performed using locally made isocentric alignment control device, target simulator and plexiglass phantom.

Results: Average isocenter shifts resulting from gantry and couch motion were respectively 1.5 mm and 2 mm. Simulating a stereotactic radiosurgery with the help of a plexiglass phantom showed less than one percent radiation leakage to critical organs such as eyes and thyroid.

Conclusion: Stereotactic collimation assembly in conjunction with the rest of constructed equipments can be employed to set up SRS treatment, provided safety and to compensate operations are taken into account. Iran . J. Radiat. Res., 2004 2 (3): 135-140

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Background: ⁶⁶Ga (t_1/2=9.49 h, β⁺: 4.153 MeV, γ: 511, 834, 1039, 2752 keV) has a wide range of applications in different fields of medical sciences. Production of ⁶⁶Ga became one of our main interests, according to its increasing applications in nuclear medicine, particularly in PET imaging.

Materials and Methods: ⁶⁶ Zn (p,n)⁶⁶Ga reaction was determined as the best choice for the production of ⁶⁶Ga, according to the present facilities and conditions. The bombardment was
performed by 15 MeV protons in Cyclone 30-IBA accelerator with a current intensity of 180 μA for 67 min. ALICE nuclear code and SRIM nuclear program were used to determine the optimum energy and target thickness. Targets were prepared by electroplating of ⁶⁶Zn (>95%) on a copper backing. Chemical processing was performed by a no carrier added method consisting of ion exchange chromatography and liquid-liquid extraction. Anion exchange chromatography was used for the recovery of target material. Quality control of the product was carried out in two steps of chemical and radionuclidic purity control.

Results: The activity of ⁶⁶Ga was 2.41 Ci at the end of bombardment (E.O.B.) and the production yield was 12.04 mCi/μAh. The chemical separation yield was 93% and the yield of chemica l recovery of the target material was 97%. Quality control tests showed a radionuclidic purity of more than 97% and the amounts of chemical impurities were in accordance with standard levels.

Discussion: Our production yield was comparable with previous reports given in the literature. The chemical separation method used in this research was simple and brought up acceptable results. So, this process can be considered as one of the best choices for the production of ⁶⁶Ga. Iran . J. Radiat. Res., 2004 2 (3): 149-158