Iranian Journal of Medical Physics
Volume:17 Issue: 2, Mar-Apr 2020

Internal exposure to radon gas progeny can lead to serious biologic damages to the lung tissue. The aim of this study was to evaluate the absorbed dose by lung tissue due to the exposure from short-lived radioactive products of radon (222Rn) decay using Monte Carlo simulation.

A lung equivalent phantom including 64 air sacs was simulated by MCNPX code. Then, the absorbed dose from short-lived radioactive products of radon decay chain including 218Po, 214Po, 214Pb and 214Bi was calculated for both suspended and deposited states of daughter nuclides inside the lung.

The results showed that alpha decay has more contribution to the lung absorbed dose in comparison with the beta and gamma decay. Furthermore, the received dose by the lung was higher when the radon progenies were deposited inside the lung so that the maximum received dose to lung was 100 times higher than that of calculated in suspended state.

Short-lived daughter radionuclides of radon decay chain, especially alpha emitter products, can be considered as dangerous internal radiation sources. The biological effects of these daughter radionuclides is more severe when are suspended inside the respiratory system.

There are some routine two-dimensional sequences, including short tau inversion recovery (STIR), T2-weighted fast-spin echo (T2W-FSE), and proton-density fast spin-echo for diagnosing osteoarthritis and lesions of the knee cartilage. However, these sequences have some disadvantages, such as long scan time, inadequate spatial resolution, and suboptimal tissue contrast which results in loss of image details, as well as missing the visualization of knee cartilage lesions. Three-dimensional (3D) sequences, such as the double-echo steady-state (DESS) sequence can decrease and overcome these problems to the smallest possible amount.

A total of 15 volunteers with knee pain were examined by a 1.5 Tesla magnetic resonance imaging.The contrast-to-noise ratio (CNR) and thickness values of the knee articular cartilage were measured. The CNR and thickness values were comparedby the Friedman test and the Wilcoxon signed-rank test.

The obtained results showed significant differences between sequences in CNR and thickness values. The DESS sequence with a flip angle of 40°showed the best CNR values and 3D fast low-angle shot (FLASH) showed the worst results. In addition, the results showed no significant differences between FLASH, 3D DESS 40° and 90° in terms of cartilage thickness. However, thickness values of these sequences were much higher than that of the PD, T2, and STIR sequences.

The 3D DESS sequence with two flip angles of 40°and 90° are the best sequences for visualizing the cartilage and the synovial fluid. Because they provide the best contrast between the cartilage and the synovial fluid, it is recommended to use DESS sequences in the evaluation of cartilage defections.

Development of higher energy modalities such as positron emission tomography/computed tomography (PET/CT), has led to more complex shielding problems. This is due to several factors, such as the radiopharmaceutical relatively high-administered activity, high patient throughput, and high energies of 511 kilo-electron volt (keV) positron annihilation photons. Therefore, this study aimed to compare three different methods used to determine the required shielding thicknesses of PET/CT facilities.

The required shielding thicknesses for three facilities were determined by using three different shielding methods, i.e. narrow beam, broad beam and Monte Carlo approximation. The design goal was chosen as 6 mSv/year for radiation workers and 1 mSv/year for the public. In addition, occupancy factors (T) were established, and all calculations had a use factor (U) of 1. The workload (W) of facilities and thicknesses of all barriers were then calculated for the three facilities.

For narrow beam approximation the average required thicknesses obtained were 6.16 mm lead, 5.12 cm concrete and 2.95 cm iron. Broad beam approximation required an average of 7.55 mm lead, 8.01 cm concrete and 2.96 cm iron thicknesses. Monte Carlo approximation required 7.62 mm lead, 10.59 cm concrete and 2.94 cm iron thicknesses.

The narrow beam approximation demonstrated the least shielding thickness required for the materials used in this study, which can lead to under-shielding. The broad beam and Monte Carlo approximations demonstrated higher required shielding thickness although there were discrepancies between these two approximations for lead, concrete, and iron.

The rate of cardiac diseases have increased among patients who underwent radiotherapy for left-sided breast cancer. The study’s aim was evaluate the dose to organs at risk in free-breathing 3-dimensional conformal (FB-3DCRT) against 3-dimensional conformal deep inspiration breath-hold (3DCRT-DIBH) in patients with left-sided breast cancer.
In total, 15th female patients diagnosed with left-sided breast cancer were included in this study from December 2017 to December 2018. All selected patients were subjected to FB and DIBH computed tomography (CT) scans. The 3DCRT plans were created on both DIBH and FB scans for each selected patient. Various doses were obtained from dose-volume histograms and then compared. The data were analyzed in SPSS software (version 20) (IBM; IL). P-value less than 0.05 was considered statistically significant.
The results obtained from the DIBH and FB conditions were compared. The average maximum dose and V95% for planning target volume  was approximate for both DIBH and FB, and the average mean doses to the heart, left anterior descending artery, and left lung were decreased by 40.50% (P=0.0003), 54.30% (P=0.02),and 18.50% (P=0.0002) in DIBH, respectively. Moreover, the heart V25% and V30% were decreased by 36% (P=0.06) and 35.8 % (P=0.03) in DIBH, respectively. Regarding the left lung, a decrease by 18.10% in V10% (P=0.0006) and 18% in V20% (P=0.0002) was also observed in DIBH.
The 3DCRT-DIBH for patients with left-sided breast cancer maintained the benefits of radiotherapy while minimizing cardiac risks. All patients completed their treatment smoothly.

Head scans are the most frequently performed computed tomography (CT) examinations worldwide. However, there is growing concern over the probability of increased cancer risks among the exposed populations. Diagnostic reference levels (DRLs) identify radiation dose that is not commensurate with clinical objectives. The aim of this study was to establish DRLs for CT head procedures and estimate effective dose (ED).
The dose absorbed by the head slice of a Rando Alderson phantom was measured using calibrated lithium fluoride thermoluminescent dosimeters (TLDs) exposed to a CT scanner operated on clinical parameters. The measurements were done at the periphery and center of the slice, and repeated twice with a new set of TLDs. The radiation dose absorbed by the TLDs was read using a Harshaw TLD reader, Model 5500. The measured doses were used to calculate the weighted CT dose index (CTDIw), CT dose index volume (CTDIv), and dose length product (DLP). Finally, the ED was calculated using the formula; ED = k × DLP, where k was considered as 0.0021.
The mean absorbed dose was 30.9 mGy, while the established CTDIv and DLP values for the head protocol were 40 mGy and 990 mGy.cm, respectively. Additionally, the ED was calculated as 2.1 mSv. These values compared well with some international values.
According to the results of the present study, the established CTDIv, DLP, and ED for head scan were well-compared with some international values, except in the cases using different scan lengths and scanner algorithms.

There are natural and artificial radioactive nuclei in our environment, as well as in the structure of the living organism. Currently, industrial and municipal pollution has also an impact on increasing the level of radiation. The present study investigated the effect of inlet water from Arak Wastewater Treatment Plant on international Meighan Wetland and assessed the radiological indicators of sediments and water samples in this area.
In this study, the specific activity of radionuclides in water and sediment samples taken from the water entry areas of the international Meighan wetland was determined using a high purity germanium detector (Baltic Scientific Instrument LTD, 005- Latvia). Radiological indices for collected samples were calculated, and the topographical maps of radiation dose distribution were plotted using Surfer software (version 13).
Specific activities of 226Ra, 232Th, 40K, and 137Cs in sediment samples were in the range of 14.44-26.58, 22.78-34.56, 360.84-447.79, and 0.7-13.03 , respectively.  The average values ​​of the external hazard index for sediment samples were calculated at 0.25.
According to the obtained results, it can be concluded that pollution is more embedded in the Treatment Plant's basin, and a small amount goes to the wetlands. Radioactivity in the research area is normal, and topographic maps show that the distance from the entrance reduces the activity of radium and increases the activity of cesium. Assessment of hazard indicators showed that radiation levels in this area are not dangerous to human health.

Treatment planning is the most important part of treatment. One of the important entries into treatment planning systems is the beam dose distribution data which maybe typically measured or calculated in a long time. This study aimed at shortening the time of dose calculations using artificial neural network (ANN) and finding the best method of training the ANN using Monte Carlo-N-particle (MCNP5) modeling.

Back-propagation learning algorithm was applied to design the neural network. The ANN was trained by MCNP5 calculations, and different kinds of methods were tested to determine the best method for training. In order to evaluate the accuracy of the ANN, the beam profiles and percentage depth dose (PDD) in the field size of 15×15 cm2 were anticipated by ANN using various training methods. Eventually, the results were compared with those obtained from the MCNP5 code.

There were good agreements between the results of comparing MCNP5 calculations with experimental measurements. Among the different training methods, Trainbfg had the least error for calculation of PDD and beam profile.

The best training method was found to be Trainbfg, and the results revealed the sufficient accuracy of the modeled ANN.

In vitro dosimetric verification prior to patient treatment plays a key role in accurate and precision radiotherapy treatment delivery. Since the human body is a heterogeneous medium, the aim of this study was to design a heterogeneous pelvic phantom for radiotherapy quality assurance.
A pelvic phantom was designed using wax, pelvic bone, borax powder, and water mimicking different biological tissues. Hounsfield units and relative electron densities were measured. Various intensity-modulated radiotherapy (IMRT) plans were imported to the pelvic phantom for verification and implemented on the Delta 4 phantom. The quantitative evaluation was performed in terms of dose deviation, distance to agreement, and gamma index passing rate.
According to the results of the CT images of an actual patient, relative electron densities for bone, fat, air cavity, bladder, and rectum were 1.335, 0.955, 0.158, 1.039, and 1.054, respectively. Moreover, the CT images of a heterogeneous pelvic phantom showed the relative electron densities for bone, fat (wax), air cavity, bladder (water), and rectum (borax powder) as 1.632, 0.896, 0.159, 1.037, and 1.051, respectively.The mean percentage variation between planned and measured doses was found to be 2.13% within the tolerance limit (< ±3%) .In all test cases, the gamma index passing rate was greater than 90%.
The findings showed the suitability of the materials used in the design of the heterogeneous phantom. Therefore, it can be concluded that the designed phantom can be used for regular radiotherapy quality assurance

This study aimed to measure the neutron contamination of flattening filter (FF) and flattening filter-free (FFF) 10-MV photon beams delivered by the Elekta InfinityTM accelerator.
The photoneutron spectrum produced by the Linac head was evaluated using a Monte Carlo (MC) simulation. The geometry and composition of the head Linac material were modelled based on information obtained from the manufacturer. In this simulation, MC N-Particle Transport Code software (MCNP6) was utilized to model the Linac head and simulate the particle transport. Evaluation of neutron contamination was carried out for the Linac with FF and without it (i.e., FFF). In this regard, the FFF beam was built by removing the FF from the Linac components. The scoring plane, as the neutron spectra calculation area for FF and FFF beams, was placed 99 cm from the target.
The neutron type produced by the head Linac Elekta InfinityTM 10-MV photon mode was mostly thermal and fast. Although there were differences in the neutron intensity of FF and FFF beams, the type of neutrons produced by these two modes had the same energy. Based on the photoneutron reaction energy threshold, it can be concluded that the neutrons produced from the head Linac were the result of photoneutron interactions of high-energy photons with molybdenum-96 and tungsten-184 isotopes.
The photoneutron quantity did not change for FF and FFF beams; however, a larger quantity of neutrons was produced in the FF beam.