Iranian Journal of Medical Physics
Volume:19 Issue: 5, Sep-Oct 2022

The present study aimed to assess the reduction of breast surface dose, breast radiation-induced cancer incidence, and mortality risks when the lead apron shielding was positioned on the chest regions during head computed tomography (CT).
In this study, routine head CT scans were performed on 28 female patients with a mean body mass index (BMI) of 25.2 ± 2.8 kg/m2. The common lead aprons (0.5 mm thicknesses) were folded and positioned in the chest regions. The breast surface doses were measured using six thermoluminescent dosimeters (TLD-100), three TLDs were located above the apron and three ones positioned under the apron. Breast radiation-induced cancer incidence and mortality risks were estimated using the Biological Effects of Ionizing Radiation (BEIR-VII) model. Finally, the measured doses and cancer/mortality risks were compared using Paired sample T-Test in SPSS software.
The breast surface doses under and over the apron were obtained at 0.18±0.06 and 0.49±0.13 mGy, respectively, (P-value<0.05). Although all cancer/mortality risks for both groups (over and under the apron) were very low, using the lead apron could decrease (significantly) breast cancer incidence risk ([1.24±0.32]×10-3 % over the apron vs. [0.46±0.15] ×10-3 % under the apron) and mortality risk ([0.30±0.08]×10-3 % over the apron vs. [0.11±0.04] ×10-3 % under the apron) about 63% in all patients.
The use of common lead aprons in the chest regions for patients undergoing head CT scans could significantly reduce the breast surface doses and radiation-induced cancer/mortality risks.

Interfractional set-up variations may cause deviation of the delivered dose from the planned dose distribution. This study aimed at calculating random and systematic set-up errors using an electronic portal imaging device (EPID) to set the optimum planning target volume (PTV) margins in patients with head and neck cancer who were under treatment with three-dimensional conformal (3DCRT) and intensity-modulated radiotherapy (IMRT).
In this study, 50 patients underwent 3DCRT along with weekly electronic portal image (EPI), and daily IMRT imaging was performed on 50 others. The EPIs were compared with Digitally Reconstructed Radiographs (DRRs) to quantify the systematic, random, and 3D vector length of set-up errors in three translational directions (X, Y, Z). The PTV margins were measured utilizing International Commission on Radiation Units and Measurements report 62, Stroom’s and van Herk’s models.
For 3DCRT and IMRT techniques, the overall mean 3D vector length of displacement was obtained at 3.9 and 2.7 mm, respectively. The maximum systematic and random errors were 1.3 and 1.9 mm for the IMRT technique and 2 and 2.9 mm for 3DCRT, respectively. PTV margins in the three acquisition directions were 2-7.2 mm.
It was found that a 7 mm extension of the clinical target volume (CTV) to PTV margin ensures that 90% of head and neck cancer patients have received 95% of the planned dose.

After lumpectomy, radiation therapy is used to control the tumor and increase patient survival. Following radiation therapy, the organs at risk are vulnerable to toxicity and secondary cancer.
Thirty-two patients with early-stage of left breast cancer were selected for this study. Intensity-modulated radiotherapy (IMRT) and three-dimensional conformal radiotherapy (3DCRT) were planned to deliver the prescribed dose to the target volume. Considering baseline risk of heart disease, the excess absolute risk (EAR) of heart disease was calculated using the Reynolds risk score for ages 50-70.
There was a significant difference in 10-year EAR of heart disease when comparing 3DCRT plans to IMRT (p <0.05). The 10-year EAR for IMRT in the low, median, and high-risk groups was superior to 3DCRT.  Among factors involved in baseline risk, by increasing the age, the impact of smoking on increasing EAR was clearer compared to a family history of heart disease. 
IMRT had a more uniform dose distribution and a better conformity-homogeneity index than 3DCRT. However, the mean heart dose and subsequently the risk of heart disease significantly were lower in 3DCRT. Considering baseline risk leads to accurate estimates of the heart disease risk after breast cancer radiotherapy.

To compare Patient-Specific Quality Assurance (PSQA) of 6 MV and 10 MV Volume Modulated Arc Therapy (VMAT) plans performed with Electronic Portal Imaging Device (EPID) kept at Isocenter 100 cm (Source to Imager Distance (SID)) using an Improved Gamma Evaluation algorithm. Previously treated patients with 6 MV IMRT for Pelvic cancers were planned, on Eclipse TPS, with 6 MV and 10 MV photon beams using VMAT technology. The PSQA was performed using EPID and investigated the effect on Area Gamma, Maximum Gamma & Average Gamma.
The mean Area Gamma passing rate (%GP±Standard Deviation(σ)) for 6 MV was 97.06±3.70, 95.42±5.31, 90.93±7.29, 86.55±9.10 and for 10 MV  97.14±6.08, 95.8±8.47, 94.62±9.45, 91.97±13.50 using the criteria 3%/3 mm, 3%/2 mm, 2%/3 mm, 2%/2 mm respectively.  Similarly, for mean Maximum Gamma value for 6 MV was 2.50±0.89, 2.72±0.94, 3.32±1.13, 3.56±1.02 and for 10 MV 2.17±0.62, 2.42±0.72, 2.84±0.90, 3.26±0.94 respectively. For mean average gamma, value for 6 MV was 0.36±0.09, 0.42±0.10, 0.45±0.12, 0.53±0.13 and for 10 MV was 0.27±0.16, 0.32±0.19, 0.34±0.20, 0.41±0.24.
There is a marked difference between Area Gamma Passing Rate of 6 MV and 10 MV photon beam. The gamma criteria of 3%/2 mm with a 5% Threshold limit and 95% Area Gamma Passing Rate can be used for PSQA using EPID at Isocenter for 6 MV and 10 MV photon beam. There is no marked significant difference in values of mean Maximum Gamma and mean Average Gamma for 6 MV and 10 MV photon beams PSQA

The study aimed to provide the dose accuracy effects between the Anisotropic Analytical Algorithm (AAA) and the deterministic solver Acuros XB (AXB) that are available on Eclipse TPS (Varian Medical Systems, Palo Alto, CA) treatment planning system (TPS).  The purpose is to investigate the difference between the AAA and Acuros XB Algorithm, The difference is due to the electron transport difference in the case of small fields.
For the study of non-small cell lung cancer (NSCLC) patient Computed tomography (CT) scans are used to do retrospective stereotactic body radiosrgery (SBRT) plans via AAA and recalculated by AXB dose calculation algorithms using the Eclipse treatment planning system. The main dosimetric comparison parameters are Conformity index (CI), Homogeneity Index (HI), Gradient Index (GI), Target mean dose, and calculation time. The Statistical analysis done by the gamma index comparison.
Based on the results, the CI is (1.45±0.55) to (1.85±0.7) (P<0.05). The HI are (0.15±0.07) and (0.13±0.08) (P<0.05), the GI for AAA was (4.8±2.6) and for AXB reaches (7.4±3.8) (P<0.05) and the maximum dose for Planning target volume (PTV) is differed about 2.3% to 4.5%, mean dose is differed about 2.4% to 3.8% and the calculation time 153±43sec and 185±76sec for AAA and AXB respectively.
The findings using the deterministic solver AXB in the calculation for the case of low density like lung cases is more accurate than AAA calculation Algorithm in SBRT treatment.

This research is a preliminary study of the development of Artificial Intelligence (AI) as a conversion tool from the pixel value of Cine a-Si 1000 Electronic Portal Imaging Device (EPID) images to dose. It also investigates the relationship between the Monitor Unit (MU), dose rate, number of frames, and beam profile of Electronic Portal Imaging Device (EPID) images to facilitate further mathematical correction that must be added to create accurate dosimetry by Cine EPID images. Homogeneous and inhomogeneous phantom was irradiated in a Linear Accelerator (Linac) 6 MV with different techniques, field size, and phantom thickness. The Cine a-Si 1000 EPID images were taken and compared to dose distribution data derived from the Eclipse treatment planning system (TPS) at Source Axis Distance 100 cm or isocenter field. The AI model training process begins with the augmentation of EPID and TPS images from homogeneous phantom so that 1152 images are obtained. These images are then split randomly into training and testing data 7:3, and validation is done using gamma index 3%/3mm. An AI model based on Convolutional Neural Network (CNN) with 6 layers has been successfully created that can convert EPID pixel values into dose distribution without any mathematical correction. The best results from validation with a gamma index of 3%/3mm compared to TPS calculations reached 92.40% ±28.14%. An AI model has been successfully created that can convert EPID pixel values into dose distribution but need improvement by considering the characteristics contained in the EPID image and the number of datasets.

Exquisite soft tissue contrast of magnetic resonance images (MRI) and the new combined radiotherapy system of MR-Linac have been the main impetus for applying MR imaging in radiotherapy. One limitation of MR-based radiotherapy is the geometric distortion of MR images that can generate errors in the contouring and dosimetry stages. This study aimed to evaluate and correct geometric distortion for radiotherapy applications.
A large field of view (FOV) phantom develop using Perspex sheets and 325 plastic pipes. The quantification and correction of MR images' system-related geometric distortion are conducted for HASTE protocol by MATLAB and 3D slicer software in phantom and patient images. The effect of MRI images geometrical distortion was evaluated for ten patients undergoing body radiotherapy treatment.  CT images were used as a primary dataset to estimate the distortion map.
The phantom investigation results indicate that in radial distances of < 13 cm (or FOVs < 25 cm), the amount of distortion is under 2 mm. Still, at more considerable radial distances, distortion may increase up to about 3.5 cm. MR images of Patients with lateral (LAT) and anterior-posterior (AP) diameters of more than 38 cm and 25 cm respectively, need to be corrected for geometric distortion.  
MR images' geometric precision in large FOVs is not sufficient for MRI only treatment planning of radiotherapy and further corrections are required. The B-spline deformable registration method can correct the MR geometric distortion until an acceptable range of 2 mm for radiotherapy applications.

The importance of estimating patient-sized adjusted radiation dose for pediatric computed tomography (CT) has long been accepted. High doses of ionizing radiation to children are often common in chest CT examinations, as the volume CT dose index (CTDIvol) is measured by a 32 cm phantom. Our study aimed to evaluate the effectiveness of size-specific dose estimate (SSDE) to compensate for the underestimated pediatric absorbed dose.       CTDIvol and dose-length product (DLP) of 320 pediatric chest CT (<1, 1-5, 5-10, 10-15 years) were obtained from Picture-Archiving and Communication System (PACS) in a hospital affiliated with the Shiraz University of Medical Sciences. CTDIvol was converted to SSDE based on the patient's effective diameter. The Statistical Package for Social Science (SPSS) was used for data analysis.    The variations between standard phantom (32cm) and the patients' mean effective diameter were approximately 65%, 57%, 47%, and 38%, across   <1, 1-5, 5-10, 10-15 year age groups, respectively.  The mean of SSDE for each age group was significantly higher than the corresponding CTDIvol values. Also, mean CTDIvol and SSDE values differed between age groups significantly (p<0.001). Results showed a strong correlation between age and the two-dose indicators, CTDIvol (0.361) and SSDE (0.184), with p<0.05.  Pediatrics receive radiation doses comparable to the dose for adult-sized patients in chest CT protocol if the dosimetry procedure is not individualized. Thus, applying a size-based conversion coefficient is paramount in estimating the absorbed dose in pediatric chest CT.