Iranian Journal of Medical Physics
Volume:17 Issue: 6, Nov Dec 2020

The present study aimed to three frequently used pulse sequences of magnetic resonance imaging (MRI) to assess the image quality of theses pulse sequences at short acquisition time.
For the purpose of study two tissue equivalent gels were prepared. One gel was made from Polysaccharide and Agarose, whereas second gel was obtained from Ferrous Benzoic Xylenol Orange (FBX) which is tissue equivalent material. 6MV photons were used to irradiate FBX gel from linear accelerator with 25 Gray dose. Imaging parameters are performed in repetition time (TR) for experimental variations. The quantitative analysis included contrast-to-noise ratio (CNR) and signal to noise ratio (SNR).
As evidenced by obtained results at 1.5 Tesla, Fast Spin Echo (FSE) and Fast Fluid Attenuated Inversion Recovery (FLAIR) were most comparable in SNR although, acquisition time of FSE is 62%, 9 %, and 15% less than FLAIR at different values of 4000ms, 4200ms and 4600ms of TR. CNR of Conventional Spin Echo (CSE) was 143% and 93% better than FSE and FLAIR respectively. The time difference between CSE and FSE was 6 min and 34 sec while this difference was 6 min and 43 sec between CSE and FLAIR.
FSE and FLAIR produced optimal image quality for many tissues. Their reduced acquisition time could make them perfect option for patients who cannot tolerate longer imaging time. Nonetheless long acquisition time cannot undervalue importance of CSE since it has yielded significantly higher contrast and SNR in T2-weighted images among other pulse sequences of MRI.

Cadmium zinc telluride has recently been used as a compound semiconductor detector in a wide range of fields. The current study is a comprehensive investigation of the performance of this detector against the photon beam. Moreover, a comparative study was carried out with other common detectors using the Mote Carlo code by the implementation of the same strategy.

During the simulation by FLUKA code, a number of photons were regarded as primary particles. It is attractive to trace each incident photon uniquely considering all possible collisions and produced secondary particles at the microdosimetry scale. In the current study, the coordinate of three-dimensional collisions location was realized at detector sensitive volume. Moreover, energy deposition was considered at each unique collision and through all interactions, totally. In addition, the physical concepts of photon interaction with detector volume were assessed, numerically. Furthermore, the effect of gold foils implemented as electrode at both sides of the detector was taken into account.

The obtained results indicated the context of photoelectric and Compton scattering in photon interactions with CZT, including the number of interactions, the deposited energy, and three-dimensional collision coordinate, while the latter case is proposed as a new achievement.

As evidenced by the obtained results, the performance of this detector can be improved by changing material fraction and detector dimension to achieve optimum efficiency. In addition, the comparative results demonstrated that the efficiency of CZT covered by gold electrodes is superior to other common available semi-conductor detectors.

Due to out-of-field effects in radiation therapy, the determination and reduction of both unwanted photon and photoneutron doses are essential for the reasonable assessment of the risks to healthy tissues.

By the application of a multilayer shield throughout the phantom and using two models for photoneutron and photon sources, doses were estimated in a 15-MV linac in tissues and organs. Different neutron moderators were used, and the best materials, such as polyethylene, polystyrene, polyvinyl chloride, paraffin, and water, were reported for shielding purpose. Boron carbide and steel were utilized as neutron and gamma absorbents. Various lengths of the shield in line with phantom stature were also assessed in this study.

Except for the target organ, with the shield throughout the phantom, both photoneutron and photon doses approximately reduced by 57-89% and 88-95%, respectively. Extra photoneutron dose in the photon source was also reported due to the shield. Then, unwanted doses, especially photon dose remarkably decreased with increasing the steel thickness. The smaller dimensions of the shield caused also a considerable reduction of the photoneutron and photon doses in the phantom.

The application of a multilayer shield reduces the photon dose remarkably in healthy tissues. Therefore, it is recommended to use shielding materials to decrease photoneutron and photon doses, which can cause a reduction in the risk of secondary cancer. Due to the relatively high mass of the shield, it is necessary to design a proper device to maintain and move the structure.

The study was conducted to compare volumetric-modulated arc therapy (VMAT) with intensity-modulated radiation therapy (IMRT) in patients with locally advanced rectal cancer (LARC). Ten computed tomography (CT) scans were selected and for each CT scan, two plans were calculated (IMRT and VMAT). The average cumulative dose-volume histograms of VMAT plans for the planning target volumes (PTVs), organs at risk (OARs), and normal tissues were calculated and compared with those reported for the corresponding IMRT technique. Target coverage was equivalent for both techniques. For primary PTV, the average homogeneity index (HI) of IMRT was significantly lower than the VMAT plans (0.10±0.04 vs. 0.11±0.03; p <0.0001). The average conformity index (CI) values for IMRT and VMAT were 1.21 and 1.12, respectively, with a nonsignificant trend for better results with VMAT (p =0.1). For the PTV boost, there was a nonsignificant trend for better results with VMAT in average HI and CI. The VMAT was superior to IMRT in OAR sparing. For monitor units (MUs), VMAT plans required 70% less MUs than IMRT. For LARC patients, VMAT was able to deliver treatment plans dosimetrically equivalent to IMRT in terms of PTV coverage. The VMAT provided better OAR sparing and significant reduction of MUs in comparison to IMRT.

Elekta Versa HD linear accelerator is equipped with a universal wedge filter which is a single large physical wedge driven by motors; in other words, motorized wedge. It provides a nominal wedge isodose angle of 60° for the field size of 30×40 sq. cm. Motorized wedge isodose distribution generated is a combination of open and wedged beam segments. With this background in mind, the present study aimed to validate the planned wedge effective isodose angle.
The current study validated the planned wedge effective isodose angle for  15°, 30°, 45°, and 60°  with 6MV and 15MV for 10x10 sq. cm and 20x20 sq. cm field size. To this end, an analytical formula was applied against a 2D array detector using PTW MultiCheck software.
As illustrated by the obtained results, the calculated, measured, and planned wedge effective isodose angle in this work represented a maximum deviation from its pre-set angle (a nominal wedge angle) of  9° for a 6MV photon energy and 5° for 15MV for field sizes of 10×10 sq. cm and 20×20 sq. cm.
In the present study, we validated the planned wedge effective isodose angle for field sizes of 10x10sq. cm and 20x20sq. cm for 6MV and 15MV photon energies using an analytical method and 2D array detector with a reasonable agreement.

Volumetric modulated arc therapy (VMAT) is an advanced technique used for radiotherapy treatment using different optimization modes. The present study aimed to evaluate Multi-criteria Optimization (MCO) influence on VMAT for Craniospinal Irradiation.

Fifteen CSI patients treated with 23.4 Gy/13 fractions followed by a boost dose of 6-MV flattening filter-free beams were chosen for this study. Conventional VMAT (c-VMAT) plans were generated for Elekta Versa HD™ linear accelerator. Keeping all other parameters constant, c-VMAT plans combined with MCO (MCO-VMAT) were created for comparison. We compared homogeneity index (HI), conformity index (CI), planning target volume (PTV) dose coverage (D98%), organ at risk (OAR) dose, normal tissue integral dose (NTID), volume receiving ≥ 5 Gy and ≥ 10 Gy by normal tissue, delivery time (DT), monitor units (MUs), and calculation time (CT).

Our findings demonstrated that HI and CI improved slightly in MCO-VMAT, in comparison with c-VMAT (P>0.05). No significant dose difference was observed in D98% for PTV and volume receiving the dose of ≥ 5 Gy, ≥ 10 Gy, and NTID (P>0.05). A slight increase was found in maximum dose to PTV in VMAT-MCO, compared to c-VMAT (P>0.05). The mean dose, max dose, and dose received by OAR were significantly lower in VMAT-MCO as compared to c-VMAT (p <0.05). The MU, CT, and DT were noticed to be lower in c-VMAT than MCO-VMAT (P>0.05).

The MCO-VMAT can be used for CSI, without compromising target coverage, reduced OAR dose by accepting a slight increase of MUs, delivery and calculation time as compare to c-VMAT.

Radionuclides found in foods are harmful to human health. Wheat and bean are among the most important food ingredients in the world. Therefore, this study aimed to determine the specific activity of natural radionuclides in wheat and bean produced near the refinery complex plant.
In order to determine the specific activity of radionuclides, the gamma-ray spectrometry method was used employing a high-purity germanium detector with a relative efficiency of 80%.
Our findings showed that the specific activity of the 226Ra isotope of radium had the ranges <1.31-5.27 and <1-5.06 Bq/kg for wheat and bean samples, respectively. Moreover, the specific activity of the 232Th isotope of thorium was in the range of not detected (ND)-4.09 and ND-3.62 Bq/kg with the mean values of 2.19 and 2.69 Bq/kg for wheat and bean samples, respectively.The specific activity of the 40K isotope of potassium was obtained as 103.19-168.94 and 129.22-568.98 Bq/kg with the mean values of 142.21 and 458.37 Bq/kg for wheat and bean samples, respectively. The annual effective dose for wheat and bean intake was 0.11-0.52 and 0.02-0.18 mSv, respectively. Furthermore, the mean of excess lifetime cancer risk for wheat and bean samples was calculated as 1.06×10-3 and 0.11×10-3, respectively. The latter values are lower than the world average for bean samples.
According to the results of this study, the radiological parameters of wheat were higher than the global average and reference value, which may be due to ash dispersion in this area. For bean, these parameters were lower than the mean value. As a result, it could be concluded that bean is not considered as a threat to consumer health.

the present study aimed to evaluate the feasibility of boron neutron capture therapy (BNCT) for breast cancer (BC) incidence during pregnancy.

Computational models of pregnant women at 3- and 6- month gestational ages were used with two different simulated tumors in their left breasts. The Monte Carlo simulation of tumor irradiation by thermal and epithermal output beams of in-hospital neutron irradiator was performed in five directions. The optimum treatment plans as a combination of the irradiation directions and output beams were then assessed using an optimization code.

Based on the findings of the present study, the total irradiation time of ≤ 10 min was needed to deliver a prescribed dose of RX = 24.4 Gy-Eq to gross tumor volume (GTV) in a BNCT single fraction. The dosimetric properties and volume metrics of the optimized treatment plans were obtained and the dose-volume histogram (DVH)-based metrics, were compared to those from conventional radiotherapy. It has been shown that the dose to both target volume and organs at risk (OARs) were within clinically acceptable dose constraints throughout the course of a single- fraction BNCT. Moreover, the fetal dose (~4.8 mGy-Eq) was well below the threshold for secondary cancer incidence (10 mGy) in the first trimester of pregnancy, while for the second trimester of pregnancy, it was much higher (~35.5 mGy-Eq).

Regarding the DVH metrics for GTV, maternal OARs, and the fetus, the studied treatment modality was an appropriate alternative treatment, especially for BC incidence in the first trimester of pregnancy.

There has been a concern about the unintended doses to critical structures outside the treatment field due to the increased risk of radiation-induced second cancer following radiotherapy treatments. Today, Monte Carlo (MC) simulation is considered the most accurate method for dose calculations in different domains of medical physics.

The Geant4 Application for Tomographic Emission (GATE) code was used to create an MC model of 6MV Siemens Primus linac. Measurements were taken in a water phantom using an ion chamber to validate the MC model. Dose profiles outside the treatment field at 1.5 (dmax), 5.0 and10.0 cm depths for field sizes from 5×5 to 20×20 cm2 were measured in the present study. Out-of-field percentage depth dose (PDD) curves at 0.0, 5.0, and 7.5 cm off axis for field size 10×10 cm2 were investigated for both measurements and simulation. However out-of-field PDDs from 10 to 15 cm off axis for field size 10×10 cm2 were studied only by simulation.

The comparisons showed agreement between the measured and simulated doses for the out-of-field profiles along the in-plane direction for all considered field sizes and depths, as well as for the PDDs at 0.0 and 5.0 cm off axis, but with less agreement at 7.5 cm off axis. All the simulated out-of-field PDDs at distances ≥ 10 cm off axis had similar trend shapes.

The developed MC model is considered a good representation of 6 MV Siemens Primus linac for the out-of-field dose calculation in lieu of measurements.

In the Swimmer’s view, the C6 and C7 can be visualized as superimposed on the shoulders. This study aimed to explore the technique to demonstrate C1 to C7 in the lateral spine and improve the diagnostic value in that region.

An experimental study was carried out using a RANDO phantom to obtain images of the lateral cervical spine. Twelve radiographs were taken using different kVps at different centering points. The image quality of the radiographs was evaluated by two radiographers using the modified image quality criteria score sheet adapted from the Commission of European Communities on image quality. A dose area product meter was utilized to estimate the entrance surface dose (ESD); however, CALDose_X5 Monte Carlo software was used to estimate the effective dose.

The findings indicated that a higher centering point at 2 inches above the pinna of the ear can clearly visualize the lower cervical spine (C6/C7) and cervicothoracic junction (C7/T1). The results of the Kruskal-Wallis test revealed significant differences (p <0.05) in the image quality at different centering points. However, no significant differences were observed (p >0.05) in the ESD between different utilized centering points. The effective dose of the modified technique was reported to be lower, compared to that for the Swimmer’s view.

The modified lateral technique can be used to replace the Swimmer’s view to adequately demonstrate the lower cervical spine and cervicothoracic junction with a lower radiation dose while not harming the patient due to movement during positioning.

We investigated the usefulness of patient-customized cast type M3 wax bolus (MWB) in radiation therapy in scalp malignant tumor patients by 3D conformal radiation therapy (3D CRT) and intensity-modulated radiation therapy (IMRT).
A helmet-type polylactic acid (PLA) hollow model was fabricated using a 3D Printing, and the molten MWB was poured into the mold and allowed to harden. Subsequently, a solid MWB head cast was obtained by removing the PLA. The radiation volume was verified using a metal oxide semiconductor field-effect transistor (MOSFET) dosimeter and EBT3 film.
Radiation dose verification was performed at the anterior, right, and left angles of planning tumor volume. The error rate demonstrated a maximum value of 5.5% and an average of 3.3% using the MOSFET dosimeter, and a maximum value of 7.0% and an average of 5.4% applying the EBT3 film. The homogeneity indices of the treatment plans were obtained as 0.09 and 0.12 using 3D CRT and IMRT, respectively. Moreover, the conformity number of the treatment plans was reported as 0.79 using 3D CRT and 0.81 applying IMRT.
The density of the MWB head cast was 1.05 g/cm3 which is closer to that of the equivalent tissue than the existing helmet type bolus material. In addition, it reduces the processing time and associated pain during custom manufacturing and has little air gaps. Therefore, it can be considered an effective method for the treatment of patients with scalp malignant tumors.