Iranian Journal of Medical Physics
Volume:20 Issue: 5, Sep-Oct 2023

During computed tomography examinations variation of dose for pediatric and adults has been increasing widely, even when automated exposure control is used. Hence, the objective of this study was to assess the computed tomography head local diagnostic reference levels in the Amhara region. Active computed tomography scanners in the Amhara region were identified and then both retrospective and prospective technique was used to collect data for pediatric and adult head examinations. Scan parameters, patient profiles, and CT dose indicators were collected from 334 patients.  Pediatric patients were grouped into three age (years) groups of (1-5, 5-10, and 10-15). The local diagnostic reference levels were established from third quartile values of computed tomography dose index and dose length product. SPSS software version 26 and Microsoft Excel 2016 were used for the entire data analysis. The calculated 3rd quartile values  of computed tomography dose index and dose length product, for adult head examinations, were 49 mGy and 1806 mGy.cm respectively. Similarly, for pediatric head CT scan, computed tomography dose index (mGy) and dose length product (mGy.cm) values for age (years) groups (1-5, 5-10, and 10-15) were (30, 2015); (35, 1221); and (43, 2051) respectively.The investigated 3rd quartile values of computed tomography dose index and dose length product were higher than other national and international reported values. For all pediatric and adult patients , there are differences in the local diagnostic reference levels between the CT centers and the same scanners, indicating the need for dose optimization.

Accurate temperature and thermal lesion prediction is very important for high-intensity focused ultrasound (HIFU) in the treatment of tumors. The traditional focal temperature and thermal lesion prediction methods usually use constant acoustic and thermal parameters. However, HIFU irradiation of biological tissue will cause its temperature rise and change the tissue characteristic parameters, which will affect the sound field and temperature field. The constant acoustic and thermal parameters, dynamic acoustic and thermal parameters, constant acoustic and dynamic thermal parameters, dynamic acoustic and constant thermal parameters were used for simulation by Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation and Pennes biological heat transfer equation (PBHTE), and their effects and differences on the focal temperature and thermal lesion of biological tissue were compared and analyzed. The focal temperature predicted by constant acoustic parameters was less than that predicted by dynamic acoustic parameters, and the thermal lesion area predicted by constant acoustic parameters was also smaller than that predicted by dynamic acoustic parameters. On the premise of using dynamic acoustic parameters, the focal temperature predicted by dynamic thermal parameters was higher than that predicted by constant thermal parameters. When the acoustic parameters remained constant, the focal temperature predicted by dynamic thermal parameters was lower than that predicted by constant thermal parameters, but their predicted thermal lesion areas were almost the same. The temperature-dependent acoustic and thermal parameters should be considered when predicting focal temperature and thermal lesion of biological tissue, so that doctors can use the appropriate thermal dose in the surgical treatment of HIFU.

Patient repositioning in treatment radiotherapy is one of the main factors that increase error of target irradiation. However additional margin is necessary to consider the uncertainties created along and around X, Y and Z-axis. Set-up and random errors were calculated in translational and rotational axis for a sample of 20 prostatic patients; using daily IGRT-CBCT method. The aim of this study was to determine the additional margin that should be added from clinical target volume (CTV) to prevent toxicity and increase the irradiation precision in radiotherapy. The van Hark formula (PTV margin =2.5Σ +0.7σ) was used for all patients to perform PTV margin for prostatic localization. The research performed for a sample of 20 consecutive patients. With respect to systematic error along the lateral axis, longitudinal and anterior-posterior was 2.32, 2.42 and 3.54 respectively. The Random error was 1.82, 2.19 and 1.76° along lateral axis, longitudinal and anterior-posterior respectively. The rotational systematic error was 1.49, 2.04 and 2.14° around lateral, longitudinal and anterior-posterior axis respectively. The Random error was 1.78, 1.75 and 1.63° around lateral, longitudinal and anterior-posterior axis respectively. The calculated safety margin to cover clinical target volume (CTV) taking the prostate variability into account measured 7.55, 8.08 and 10.79 mm for lateral, longitudinal and anterior posterior respectively and 7mm would be enough in the posterior side. Rotational set-up errors for almost 95% of patients were between -2° and 2°. The calculated safety margin in all direction was smaller than 1 cm except in anterior side that was 1 cm or more.

Mobile phone users and base stations have increased exponentially in recent decades. These expansions have extended worries about the potential risk of long-lasting Radiofrequency Electromagnetic Fields (RF-EMF) exposure on human health and environmental quality. The current study was designed to explore the cytogenetic consequences of subjecting two biological systems to RF-EMF at a frequency of 1800MHz and a specific absorption rate of 0.27 W/kg.
Chromosome aberration test (onion meristematic cells) and micronucleus assay (mouse erythrocytes) were used to evaluate the potential cytotoxic and genotoxic effects of the in vivo exposure to RF-EMF at a frequency of 1800 MHz. The two living systems were subjected to RF-EMF for 0, 0.5, 1, 2, and 4 hours daily for seven successive days. We recorded the percent aberrant cells (%Abc), the percentage of micronuclei formation in erythrocytes (%MN), and the percentage of micronucleated polychromatic erythrocytes (%MNPCE).
It was demonstrated that the short- and intermediate-term exposure to RF-EMF may cause a gradual time-dependent boost in root growth. However, significant growth inhibition was observed following 4-hour exposure. Exposure to RF-EMF did not change mitotic indices of onion meristematic cells. Significant increases in Abc, MN, and MNPCE percentages were recorded.
The outcome of this study proposes that unlimited exposure of living organisms to RF-EMF may lead to adverse effects. Therefore, unnecessary use of mobile phones should be avoided.

In radiotherapy treatment of head and neck (H&N) cancers, more complex quality assurance checks and patient-specific dosimetry are required to ensure accuracy in modern technology. In this paper, a new cost-effective human tissue equivalent H&N phantom was designed to serve as an economical and adaptable tool for assessment and assurance of precise radiotherapy dose delivery.
The phantom was designed using locally available paraffin wax and tissue-equivalent materials. Computed tomography (CT) images of the phantom were acquired using a conventional CT simulator and were registered with the images of a real patient having approximately similar physical dimensions. The geometric and attenuation properties of the structures in the phantom were studied and compared to the structures of the real patient. 
Hounsfield unit (HU) values of different structures of the phantom were compared to the values obtained from the CT images of a real patient and were found to be in good agreement. HU values obtained for the right, and left eye, brain, larynx, and bone shell were 7(±10) HU, 6(±9), 30(±14) HU, -984(±6) HU and 873(±214) HU in phantom. Structures simulated in phantom agreed well on comparison regarding both their design and radiation properties with respect to real patient human tissues. Gamma analysis was performed for the axial dose plane at plan isocenter for both the calculated dose distribution in H&N phantom and the patient agrees for 98.79% passing rate for 3% /3mm criteria.
The designed phantom depicts human anatomy and meets the requirements of tissue equivalence. The result shows that phantom has proved to be a cost-effective and valuable tool for accurate verification of dose distributions in regions of clinical and dosimetric interests.

This study quantifies the dosimetric impact of lateral and longitudinal positioning errors on left-sided breast cancer during 3D conformal radiation therapy, employing both mono isocenter (MIT) and double isocenter technique (DIT) irradiations, and explores the frequency dependence of these errors.
The study includes 10 left breast cancer patients, with two reference treatment plans created for each using both MIT and DIT techniques. Positioning errors of 2mm and 4mm in the right and inferior directions were simulated across varying error repetition scenarios (1 time, 5 times, 10 times, and 25 times) throughout the 25-fraction treatment period. Statistical analysis employed paired samples Student t-tests with a significance level of α<0.05.
Dosimetric impact was observed in MIT and DIT-TG (breast isocenter) plans for the heart, and in MIT and DIT-SC (supraclavicular isocenter) plans for the spinal cord. DIT-SC, being close to the spinal cord, demonstrated sensitivity to small lateral isocenter movements, impacting spinal cord dosimetry. Similarly, the heart and isocenter position in DIT-TG plans were susceptible to right-directional errors, affecting dosimetric parameters of these organs-at-risk.
Even minimal errors, measured in millimeters, can significantly influence heart and spinal cord dosimetry, potentially leading to heightened post-treatment toxicities, particularly when reference plan doses are close to recommended limits. The study advocates for vigilant repositioning accuracy control in DIT plans during each treatment session. Encouraging the use of MIT, when feasible, emerges as a crucial consideration to mitigate dosimetric variations and enhance treatment precision.

Machine-learning models have been widely used to predict dose distribution in therapy planning such as Intensity Modulated Radiation Therapy (IMRT). Random-forest is one of the machine learning models which can reduce output bias by using the average value all of estimators. Planning data in Digital Imaging and Communications in Medicine (DICOM) format is exported to Comma Separated Values (CSV). Then, used to random-forest algorithm that will be trained using 7-fold validation and then the model will be evaluated with new data, i.e., data that the model has never seen before. The data evaluated were the parameters to obtain Homogenety Index (HI) for the target organ, whereas the mean and max dose for organs at risk (OARs) were evaluated. Statistical analysis were also carried out to assess the significant difference between the predicted value and the true value. Random-forest was able to predict the true value with errors evaluated using Mean Absolute Error (MAE) on Planning Target Volume (PTV) features D2 (0.012), D50 (0.015) and D98 (0.018) as well as at OAR features (Dmean and  Dmax) of the right lung (0.104 and 0.228), left lung (0.094 and 0.27), heart (0.088 and 0.267), spinal cord (0.069 and 0.121) and (V95) Body (0.094). Based on the results of statistical tests, p >0.05, there is no significant difference between the two data. Random-forest regressor is able to predict the dose value with the smallest difference in PTV features.

It is necessary to understand the importance of different energies in Fractionated Stereotactic Radiotherapy (FSRT) plans for better outcome. The study objective is to compare FSRT plans with Flattening Filter (FF) and Flattening Filter Free (FFF) beams. Twelve patients with primary Brain Metastasis (BM), were selected and given 25 Gy in five fractions for which 6FF beams were angled in double arc. The Planning Target Volume (PTV) and Organs at Risk (OARs) were assessed using dosimetric indices after each plan was replanned with 6 FFF, 10 FF, and 10 FFF energies. Treatment time (TT) and Monitor Units (MUs) were also compared. Additionally, we compared portal dosimetry for dose agreement across all plans using the gamma analysis criterion. PTV parameters of created plans showed better values when compared to 6 FF plans, where the most significant is with FFF plans which include D98%, D80%, D2%, D50% and Dose Gradient Index values of 6FFF plans. Among OARs, the most significant is the V10 value of (Brain-PTV) as (46.77±43.9) and maximum dose values of optic chiasm, brainstem, and left lens in 6FFF plans. Among technical parameters, the 6FFF plan showed significant TT value of (3.06±1.0) with p-value 4.13E-05. Better gamma analysis passing rates were achieved with FFF beams. Linear accelerator-based FSRT delivery of BM using 6 FFF beam results in better dosimetric indices, OAR sparing, fastest treatment delivery, and energy conservation with reduced peripheral and out-of-field dose for higher treatment modalities like Rapid arc.