Iranian Journal of Medical Physics
Volume:18 Issue: 4, Jul-Aug 2021

Quality assurance is necessary for every IMRT plan.‎Octavius 4D-1500 detector phantom is ‎one of the new phantoms for ‎determining the treatment plan quality‎.‎ This study aimed to examine the IMRT plans using the ‎Octavius 4D-1500‎‏ ‏‎to determine if ‎it is a reliable, ‎dependable, and durable. 

IMRT QA conducted for 30 cases: HN and pelvis. The Monaco TPS used for treatment planning. The treatment plans ‎were then applied ‎to the Octavius 4D-1500 phantom (virtually and actually), ‎‎the γ-index was calculated in VeriSoft program to evaluate the IMRT plans.

Significant differences were observed between the ‎‎‎measured and calculated dose distributions for HN and pelvic plans, while the treatment ‎sites did not affect the GP rate. The results of the global Gp ‎ were higher than the local GP, ‎regardless of the study criteria. The ‎HN plans ‎showed a more significant difference ‎than the pelvic plans. The HN plans, ‎a ‎strong significant correlation was found between the total ‎fields’area and %GP in both global ‎‎and local analyses, while in the pelvic plans, there was only a significant association with the ‎local %GP.

The measured dose distributions significantly different from calculated distributions. The relationship between the ‎‎fields’ ‏‎ area ‎and ‎‎‎%GP was inverse. In the HN plans, a ‎significant correlation found between the total ‎‎fields’ ‎area ‎and %GP in both global and ‎local, while only local %GP in the pelvic plans was significant correlation. Overall, the Octavius 4D-1500 detector phantom ‎might be applicable for ‎assessing the QA of IMRT plans.

Cancer patients receive radiation therapy (RT) as part of their treatment as monotherapy or as part of a combination treatment. Radiation therapy uses high-energy radiation such as photons and strong ions. Nanoparticles (NPs) are used for magnetic hyperthermia, which increases the efficacy of RT and generates heat to kill cancer cells by destroying their DNA.           
Nanoparticles were prepared using the co-precipitation method and characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffractometer. Fifty-six male mice were housed under similar environmental conditions. The animals were injected into the right flank with 0.25 mL of 106 cells/mL Ehrlich tumor suspension. When tumors reached 5-10 mm in diameter, the mice were randomly divided into eight groups as follows: 1st group: used as the control group injected with 25 μL of phosphate buffer saline without treatment, 2nd group: injected with Fe3O4-NPs, 3rd group: injected with Fe2O3-NPs, 4th group: injected with methotrexate (MTX), 5thgroup: injected with MTX, Fe3O4, and Fe2O3-NPs, 6th group: as the 5th group with microwave hyperthermia, 7th group: as the 5th group then treated with high-energy photons, and 8th group: as the 5th group and exposed to electron beam therapy. Tumor volume and weight were measured after 15 days. Tumor apoptosis was studied using histopathology, and the tumor's side effects on the biological systems were investigated.
The results indicated that magnetic hyperthermia with microwave and linear accelerator treatment coupled with drugs was suitable for cancer treatment. A significant decrease in tumor size, tumor necrosis, and fibrosis was observed.
It was found that Fe3O4 and Fe2O3-NPs coupled with MTX and exposure to photon and electron beam therapy and microwave radiation are the best methods for cancer treatment.

Nowadays, the absorbed dose of patients is on the rise due to the widespread use of computed tomography (CT) during the diagnosis process. Patients' doses for similar procedures are very different due to diversity in scanners and protocols. Hence, the purpose of this study was to determine the diagnostic reference levels for routine CT scan procedures in Kohgiluyeh and Boyer-Ahmad province, Iran. In this study, four common brain, sinus, chest and abdominopelvic procedures (overall 200 scans) in spiral mode were selected in five CT centers of Kohgiluyeh and Boyer-Ahmad province, Iran. Next, the doses were measured in head and body phantom, based on scan parameters of ten patients in each procedure at each centers (200scans). Then, the third quartile of CTDIw was considered as the diagnostic reference dose. Finally, considering the pitch factor and the mean scan length in each protocol, the diagnostic reference level values based on the third quartile of the dose length product (DLP) and volume CTDI (CTDIvol) were determined. The dose reference level values according to CTDIw third quartile in the brain, sinus, chest and abdominopelvic procedures were 39.82, 20.88, 14.10 and 17.07 mGy, respectively. In terms of dose length product, the diagnostic reference level values in the above procedures were determined to be 702.75, 243.90, 422.02, 865.62 mGy.cm, respectively. The DRLs of the CTDIW, DLP and CTDIvol of brain and sinus scans calculated in this study, were comparable to other provinces, national DRL and eight other countries. However, the same quantities for the chest and abdominopelvic scans showed higher values compared to the mentioned studies, suggesting lowering mAs and increasing pitch number for patient’s dose optimization. In some centers to preserve image quality, it is necessary to optimize radiation conditions, especially for chest and abdominopelvic scans.

Computed tomography dose index (CTDI) phantoms are used to optimize CT examinations in terms of image quality and the received dose. In this study, we aimed to develop cost-effective head CTDI phantoms from polyester-resin (PESR) materials as alternative phantoms. The PESR was mixed with methyl ethyl ketone peroxide (MEKP) as a catalyst. The ratios of MEKP to PESR were 1:150, 1:200, 1:250, and 1:300, respectively. The phantom dimensions were designed similar to the standard CTDI phantom, i.e., length of 15 cm and diameter of 16 cm with five holes (diameter, 1.31 cm). The CTDI measurements using the PESR-MEKP phantoms were compared with the CTDI measurements using the standard polymethyl methacrylate (PMMA) phantom. The results showed that the CTDI valuesof the PESR-MEKP phantoms were slightly higher (up to 6%) than the standard PMMA phantom. It was found that the CTDI measured by the PESR-MEKP phantom with a ratio of 1:300 had the least significant difference from the standard PMMA phantom; also, at this ratio, the phantom was the most homogeneous. The head CTDI phantoms based on PESR-MEKP materials were developed and evaluated in this study. It was found that the PR-MEKP phantom with a MEKP-to-PESR ratio of 1:300 was insignificantly different from the standard PMMA phantom. Also, the phantom was constructed easily at a more reasonable cost, compared to the standard phantom.

In yttrium-90 imaging, image quality is highly dependent on the selection of energy window and collimator design becausetheY-90 bremsstrahlung photons have a continuous and broad energy distribution. The current study aimed to optimize the bremsstrahlung energy window setting and collimator for the improvement of both resolution and sensitivity. In the present study, simulation of medical imaging nuclear detectors (SIMIND) Monte Carlo program was used to simulate Siemens Medical System Symbia. The SIMIND was utilized to generate the Y-90 bremsstrahlung single-photon emission computed tomography (SPECT) projection of the point source. Six energy windows settings and two collimators denoting medium energy and high energy were used in order to assess the effect of the energy window on the resolution. The experimental measurements and simulation results showed a similar pattern in the point spread functions with the energy window. The simulation data indicated that the geometric component reached 73%for the energy window within the range of51-120keVusingthe high-energy (HE) collimator. In addition, the obtained results showed that the full width at half maximum (FWHM) and full width at tenth maximum (FWTM)(FWHM=7mm and FWTM=35mm)were higher in this window in comparison to those reported for other windows. According to the obtained results of the present study, the optimal energy window for Y-90 bremsstrahlung SPECT imaging was within the range of 51-120 keV. The obtained optimal energy window and optimal HE collimator had the potential to improve the image resolution and sensitivity of Y-90 SPECT images

In various radiotherapy techniques for breast cancer, the inclusion of internal mammary nodes (IMNs) in the target volume is important for selecting the most appropriate technique. This study aimed to compare three radiotherapy techniques with the inclusion of IMNs regarding the dose homogeneity index (DHI) of regional lymph nodes and the chest wall, besides the dose received by the heart and the left lung.

Three radiotherapy techniques were planned for CT imaging of the RANDO phantom, including the wide tangent (WT); oblique parasternal photon (OPP); and oblique parasternal electron (OPE) techniques. The doses reaching the contoured organs were compared between the three techniques, using the data gathered from the thermoluminescent dosimetry and treatment planning system.

The OPE technique produced a lower absorbed dose for the left IMNs, compared to the other two techniques. In the OPP technique, the dose received by the left lung was higher than its tolerance, while the lung dose in the OPE technique was slightly lower than the WT technique. The absorbed dose by the heart was the lowest in the WT technique; also, the DHI value was better for this technique than the other two techniques.

The WT technique showed better results regarding the dose homogeneity distribution of IMNs and the chest wall, as well as protection of organs at risk.

In this survey, radiation-induced secondary cancer risks (SCRs) have been assessed in irradiated organs following three-dimensional conformal radiation therapy (3D-CRT) of breast cancer using the Biological Effects of Ionizing Radiation (BEIR) VII models.
Sixty patients with left-sided breast cancer, who were treated with a total breast dose of 50 Gy in 2 Gy fractions were chosen for this study. Differential dose volume histograms (dDVHs) were retrieved, and values of mean organs dose were computed. Second cancer risks for the heart, ipsilateral lung, liver, thyroid, and contralateral were estimated using both excess relative risk (ERR) and excess absolute risks (EAR) models as proposed by the BEIR VII committee of the U.S National Academy of Sciences.
The mean organ dose values of these 60 patients were 6.8, 15.9, 3.7, 4.5, and 1.5 Gy in the thyroid, ipsilateral lung, contralateral breast, heart, and liver, respectively. Based on the BEIR VII models, ERR was estimated to be 21.2, 5.0, 1.6, and 1.4 Gy-1 for the ipsilateral lung, thyroid, heart, and liver, respectively. In addition, excess absolute risks for cancer incidence were calculated as 105, 45.8, 15.8, and 4.35 Gy-1 for these organs, respectively.
In this survey, SCRs were quantitatively measured for various organs of breast cancer patients who received 3D-CRT. We observed that 3D-CRT treatment was associated with a relatively high SCR in the lung.

The success of radiation therapy depends critically on the accuracy of patient alignment in treatment position day after day. The primary use for Electronic portal imaging devices (EPIDs) is to monitor patient position during daily radiotherapy sessions. Recently the role of EPIDs has been expanded beyond patient imaging to become a useful tool for radiotherapy dosimetry.

To test another application of linac quality assurance (QA), 10×10 cm2 and 18×18 cm2 images of an open field were obtained. The epidermis was located at a fixed detector distance of 150 cm.

Wedge profile and wedge factors with a high level of accuracy demonstrated. The profiles acquired using EPID deviated in shape and magnitude by up to 16% from the ion chamber profiles. The use of EPID for linac QA can be simplified by improving the available software analysis tools, which will increase its efficiency. According to the findings, the EPID aSi500 has the potential to be used as a relative dosimeter, making it a straightforward and efficient tool for daily QA.

All EPID measurements were performed using the linear accelerator Varian DMX. Based on the physical characteristics, as an efficient tool, the SLIC-EPID can be used for daily QA.

Using the small field in modern radiotherapy, the present study aimed at measuring the relative dosimetry (scattering factor, percentage depth dose (PDD), and profile of penumbra) with ionization (FC65-G, CC13, CC01) and diode (razor) chambers.

Applying TRS-398 in Varian Clinac™ IX-5982 for 6 MV photon beams, the conditions (pressure, temperature, direction, polarity) were kept the same for a set of field sizes (1 × 1, 2 × 2, 3 × 3, 4 × 4, 5 × 5, 7 × 7, and 10 × 10 cm2), and relative dosimetry was performed at the North-East Cancer Hospital, Sylhet, Bangladesh.

During the output factor measurement in small fields, the razor showed better results than CC13. Taking CC01 as a standard in small fields, the data obtained from the study showed a good agreement with those of the previously published works.

Razor, with extremely small active volume, was very much suited for small field dosimetry, except for PDDs.