Iranian Journal of Medical Physics
Volume:16 Issue: 5, Sep-Oct2019

Radioactive material is always present in the environment, and the largest contribution to the inhalation exposure comes from the short half-life decay products of radon. Accordingly, the concentrations of radon were measured in the milk and tea samples collected from Misanmarkets in Iraq. A total of 20 samples were taken to the laboratory in the School of Physics for sample preparation and then determined using LR-115 detector. The concentrations of radon measured in milk samples were observed to vary from 32.0 to 180.4 Bq/ m3 in Celia 1 and Primer samples, respectively, with a mean value of 109.92Bq/ m3. However, the obtained results of radon concentration in the tea samples were noticed to vary from 40.0 Bq to 220.0 Bq/ m3 in aeroplane and appeared samples, respectively, with a mean value of 158.64Bq/ m3. The radon concentration in the tea samples was higher than that in the milk samples. The result showed the radon concentration varied according to different kinds of samples depending on the source of samples. The concentrations were below than the action levels of 200-600 Bq/ m3 as recommended by the International Commission on Radiological Protection. According to the results, the collected samples did not pose any major threats.

The risk of radioactivity addresses human life directly. The natural rock radioactivity is mainly due to 232Th, 238U), and 40K series. Activities involving blasting, crushing, and processing of rocks into numerous pieces lead to release of radionuclides into the atmosphere in the form of dust particles. Sixteen soil samples were collected from various locations of the Al-Samawah desert, Al-Muthanna Governorate, Iraq. The specific activities of 238U, 232Th, and 40 K were measured using NaI(Tl) 3''x3'' gamma-ray spectroscopy. It is demonstrated that 238U, 232Th, and 40K were 11.53±0.76, 8.70±0.43, and 319.27±4.4 Bq/kg, respectively. The specific activity values were lower than the recommended United Nations Scientific Committee on the Effects of Atomic Radiation values. The Hex with the mean of 0.131 ranged from 0.094 to 0.171. The range for D, Raeq, and total AEDE were obtained as 17.468-30.967 nGy/h, 34.956-63.173 Bq/kg, and 0.02-0.038 mSv/y, respectively. Moreover, the means of dose rate, radium equivalent activity, and AEDE were 23.893 nGy/h, 48.549 Bq/kg, and 0.029 mSv/y, respectively. The low mean of Hex, is found to be < 370 Bq/kg. Results showed that the mean specific activity of 238U, 232Th, and 40K nuclides were lower than the worldwide recommended values. Furthermore, the Hex values for all the soil samples were lower than unity and Raeq as another good indicator was below the value considered as hazard (370 Bq/kg).

One of the useful standard quality assurance techniques in radiation therapy is monitoring entrance doses in in-vivo dosimetry. An overall tolerance limit of 5% of the absorbed radiation dose has been recommended by the International Commission of Radiological Units. The implementation of an in vivo dosimetry still remains as a challenge to clinical medical physicists. As a result, the practice of constant monitoring of patients undergoing radiation therapy in most of the radiotherapy departments in Africa has not been given much attention. The study aimed at the evaluation of in-vivo entrance dosimetry using diodes to verify the accuracy of the radiation delivered to patients, compared to prescribed doses.

In this paper, a protocol for in vivo dosimetry using a two flat surface Sun Nuclear Corporation diode in a radiotherapy department has been implemented in equinox Cobalt 60 beams. A water phantom calibrated was performed using the International Atomic Energy Agency standards (TRS 398). Calibration coefficients were determined with diodes using a Perspex phantom to derive correction factors. A total number of 137 patients’ doses were measured with the diodes during the treatment of 4 different sites.

The average deviation between the measured and expected entrance dose performed by the phantom studies was 5% (0.34±1.8%) in almost all cases.

The developed protocol in this study indicates that in vivo dosimetry using silicon diodes is reliable, which can be adopted as a universal quality assurance tool in the radiotherapy departments. Moreover, measurements with diodes can be acquired online which produces an instant readout and is relatively cheaper as compared to the ion chamber.

The evaluation of X-ray and light field coincidence in linear accelerators as a quality control test is often performed subjectively, involving the manual marking of films and their visual inspection following the irradiation. Therefore, the present study aimed to develop an objective method for the performance of this test leading to the increased levels of accuracy, precision, and speed for the measurement of X-ray and light field coincidence.

The new method involved a portable, lightweight, and inexpensive device containing optically-shielded and non-shielded photodiodes to detect the location and dimensions of the light and X-ray fields. The obtained results were analyzed using purpose-written user-friendly software.

On the basis of the results, this system could be a reliable method to measure the coincidence of the two fields with the accuracy of 0.5 mm and average field size standard deviations of Elekta Presice and Siemens Primus are 22.47 mm2 and 22.36 mm2, respectively. The result was well within the tolerance recommended by the American Association of Physicists in Medicine task group report number 142.

The proposed method allows accurate and precise measurements through a largely automated process. Therefore, the measurement results benefit from the reduced level of subjectivity or human error, compared to the standard film-based technique.

Due to nuclear interactions between the tissues and high-energy protons, the particles, including neutrons, positrons, and photons arise during proton therapy. This study aimed at investigating the dose distribution of proton and secondary particles, such as positrons, neutrons, and photons using the Monte Carlo method.
In this study, a beam of protons was utilized with the energies of 160 and 190 MeV, which are more popular for brain tumor treatment. This beam irradiated the brain phantom after passing through proton therapy nozzle components. This phantom has a tumor with a radius of 3 cm in its centre. The most important parts of the nozzle include magnetic wobbler, scatterer, ridge filter, and collimator.
The results show that while using protons with the energy values of 190 and 160 MeV, the equivalent dose fractions in tumor, brain, skull, and skin to the total equivalent dose in the head are 61.8 (62.4%), 10.4(10.9%), 6.07(3.69%), and 21.7(23%), respectively, regarding the primary and secondary particles.
According to the obtained results, in spite of the fact that most of the equivalent dose was inside the tumor volume, the skin of head has received the noticeable dose during proton therapy of brain which needs more concern.

An operational computed tomography (CT) scanner is a major source of human exposure to ionizing radiation. Exposure increases the risk of cancer and aplastic anaemia. All radiation exposures should be justified and optimized to meet the clinical objective. In order to avoid the administration of excessive radiation dose to patients, diagnostic reference levels (DRLs) were proposed. The DRLs identify unusually high radiation doses during CT procedures, which are not commensurate with the clinical objective. They have been successfully implemented in Europe, United States, some developed countries, and a few developing countries. In this regard, the present study aimed at establishing DRLs for the head, chest, and abdomen/pelvis CT procedures at a tertiary hospital in South Africa.
A retrospective analysis of volume CT dose index (CTDIvol) and dose length product (DLP) was performed on 100 randomly selected adult patients for each of the head, chest, and abdomen/pelvis CT procedures. The mean values of the DLP and CTDIvol dose parameters were calculated using SPSS, version 24.  
The established DRLs for CTDIvol were 32; 7, and 32 mGy for the head, abdomen/pelvis, and chest, respectively, while the DLPs for the respective protocols were 767, 386, and 593 mGy.cm.
The implementation of DRLs facilitates identifying CT doses that are not commensurate with the clinical objective, thereby lowering patients’ doses significantly.

Dose distribution can be affected by diverse parameters, such as beam orientations, and collimator angles. These parameters should respect and maintain the international recommended levels during the realization of the quality assurance protocols of linear accelerators. This study aimed at evaluating the dosimetric effects on treatment quality considering the mechanical error fluctuations in the recommended range.
This study included ten patients with head and neck cancer. All of them were treated using three-dimensional conformal radiotherapy with the simple 3-field classic technique. Initially, an optimized treatment plan was computed for each patient. Afterward, similar calculations were executed by varying isocenter position, gantry and collimator angles. Eventually, dosimetric evaluations based on dose-volume histograms were studied and analyzed by Wilcoxon signed rank test for each plan.
The analysis of the dose-volume histograms of tumor volumes and organs at risk, as well as the dosimetry calculation, revealed that the small errors of 0.5° in gantry and collimator angles have minimal effects on dose distribution. However, the variation in isocenter coordinating up to 1 mm may influence the patients’ treatment quality, particularly in the spinal cord and the brainstem, in which Wilcoxon's test showed significant effects in all plans.
According to the results, the quality of the treatment plans is almost insensitive to the errors of the gantry and the collimator angles of the order 0.5° though it is relatively sensitive to isocenter errors (1 mm). These should be reduced in order to avoid overdose when applying the conventional 3-field technique.

Previously, 186Re and 188Re radioisotopes have been produced through appropriate activities, and each of them has been used for therapeutic applications. The 186Re and 188Re have unique properties, which make them proper for the treatment of  tumors in different sizes. The long-range 188Re, is suitable for the annihilation of large tumors. In contrast, the short-range 186Re is desirable for the destruction of small tumors. The aim of this study was to find the suitable time for rhenium irradiation in order to simultaneously produce radionuclides with both appropriate and identical activities.
To reach 186Re and 188Re with appropriate activities to produce compositional radiopharmaceutical, we have investigated natural rhenium irradiation at different times to produce 186Re and 188Re simultaneously with appropriate and identical activities to reach compositional radiopharmaceutical. In this regard, the simultaneous production of 186Re and 188Re with appropriate activities were investigated analytically through natural rhenium irradiation in a reactor. The irradiation was assessed at different time intervals in order to reach appropriate activities for compositional radiopharmaceuticals.
On the basis of the findings, 186Re and 188Re could be produced simultaneously with suitable and almost equal activities with irradiating natural rhenium for 4 days and considering 1 day for cooling. Moreover, the obtained results of this study revealed that the generated impurities were negligible.
The optimization of natural rhenium irradiation time can help the simultaneous production of 186Re and 188Re with appropriate activities for compositional radiopharmaceuticals.

Digital radiography possesses a wide dynamic range and has a major advantage in producing an acceptable image of diagnostic value even though overexposure occurs. Lumbar spine (LS) radiography is the most common examinations that gives high radiation dose to patients and accounts for the highest collective population dose of any conventional radiographic examinations. As such, this study was carried out to ascertain the impact of image quality and entrance surface dose (ESD) with different exposure settings in the anteroposterior (AP) and lateral LS.

The torso of the PBU-50 phantom was exposed to medium and high kilovoltage peak (kVp). A total of 14 images for LS were obtained. Relative image quality was assessed using Leeds Test Objects TOR CDR whilst the ESD was ascertained using an optically stimulated luminescence dosimeter.

The results of Friedman test indicated a significant difference in image quality when using medium and high kVp. Wilcoxon signed-rank test also reflected a significant difference in ESD between the use of medium and high kVp for both AP and lateral LS.

Significant differences in image quality and ESD were obtained using medium and high kVp with medium kVp resulting in high contrast but low contrast sensitivity and vice versa. The findings of the present study indicated that the recommended kVp for AP LS was from 75kVp to 81kVp whilst for lateral LS the recommended kVp was from 85kVp to 90kVp for an average adult patient.

Long bone examination in standing position, as one of the diagnostic methods in plain radiography, is most commonly used in the field of medical diagnosis, especially leg length discrepancy. However, with regard to this examination, reproductive organs are exposed to radiation as they are placed in the adjacent area to the long bone. Due to the sensitivity of gonads to radiation, their exposure must be kept as minimal as possible to the extent to which proper diagnosis is feasible in order to reduce tumor growth in lower extremity examination. The purpose of this study was to optimize the radiation dose in the long bone examination in standing position.
This experimental study was conducted to evaluate the radiation exposure dose to a phantom and estimate effective doses and organ-specific doses (i.e., testes and ovaries) among patients using PC-based Monte Carlo program. 
A phantom examination in the posterior-anterior (PA) configuration produced a radiation dose nine and three times smaller than those in the anterior-posterior (AP) and AP with shielding configurations, respectively. In a patient study (PA configuration), the testes, ovaries and effective doses were estimated at 15, 1.2, and 2 times smaller than those in the AP configuration, respectively.
This study demonstrated that examinations in the PA configuration produce a smaller radiation dose than those in the AP configuration.

Geometric distortion, an important parameter in neurology and oncology. The current study aimed to design and construct a new three-dimensional (3D) phantom using a 3D printer in order to measure geometric distortion and its 3D reproducibility.

In this study, a new phantom containing 13,824 reference features (control points) was designed with AutoCAD software, fabricated with a 3D printer, and filled with vegetable oil. This phantom was tested on the Siemens 3 Tesla Prisma MRI model using a 64-channel head coil. Six-slice computed tomography (CT) scan images were used as a reference. Moreover, the reference features of MRI images were matched with those of CT scan images using a 3D reference model. The reproducibility of the phantom was investigated on three different days (three different imaging sessions per day).

The obtained 3D results indicated that the non-uniformity of field and nonlinearity of the gradients and imaging reproducibility could lead to geometric distortion. The mean Euclidean distance error for MRI volume was less than 1 mm. The maximum Euclidean error was 1.5 mm. Distortion in the whole volume was pronounced more specifically at the edges of the magnetic field.

The results showed that the amount of distortion in the middle of the field was less than at its sides. This phantom can be used to check the distortion filters on the device. Furthermore, this phantom can be used to study geometric distortion in scenarios that require a small study volume, such as prostate studies.

We aimed to dosimetrically compare three-dimensional conformal radiotherapy (3D-CRT) and volumetric modulated arc therapy (VMAT) in terms of planning target volume (PTV) coverage, organ at risk (OAR) sparing, and conformity index (CI).

Planning data of 26 high grade glioma (HGG) patients were used. Prescribed dose for 3D-CRT was 46Gy in 23 fractions to low-risk PTV (LR-PTV) and 14 Gy in 7 fractions to high-risk PTV (HR-PTV). VMAT plans were conducted using 46 Gy in 30 fractions to LR-PTV and 60 Gy in 30 fractions to HR-PTV.

Tumor locations were frontal, parietal, temporal, and multi-lobed in 27%, 15%, 23%, and 35% of cases, respectively. Histology was glioblastoma multiform in 89% of patients. Mean values of PTV D95 (dose received by 95% volume) in 3D-CRT and VMAT were 96.6% and 98.8% for the LR-PTV and 97.3% and 99% for HR-PTV (P<0.001), respectively. Mean values of CI in 3D-CRT were 0.96 and 0.97 for LR-PTV and HR-PTV and 0.98 and 0.99 for LR-PTV and HR-PTV of VMAT (both P<0.001), respectively. Mean Dmax of right optic nerve (maximum point dose received by the organ) for 3D-CRT and VMAT were 31.59 and 25.57Gy (P=0.02). Mean Dmax for left optic nerve and optic chiasm were 28.81 and 22.14 Gy (P=0.019) and 42.24 and 37.12 Gy (P=0.055) respectively for 3D-CRT versus VMAT. Doses to other OARs were not statistically different between 3D-CRT and VMAT.

VMAT achieved better coverage of the PTV and delivered fewer doses to bilateral optic nerve and chiasm.