Iranian Journal of Medical Physics
Volume:18 Issue: 3, May-Jun 2021

To study the impact of 6 MV and 10 MV flattened beam (FB) and flattening filter free (FFF) beam in whole brain radiotherapy (WBRT) by using volumetric modulated arc therapy (VMAT).
Twenty WBRTpatients were selected randomly. The dose prescription was 30 Gy, which was delivered in ten fractions. The planning target volume (PTV) and organs at risk (OARs) were contoured. Four VMAT plans, including 6 MV FB, 6 MV FFF, 10 MV FB, and 10 MV FFF beam plans, were generated.
The 6MV FB and FFF beam plans were statistically significant (p<0.05) in terms of the dose received by 98% of the PTV (D98%) (26.86 Gy vs. 27.31 Gy, P=0.006), the dose received by 95% of the PTV (D95%) (28.28 Gy vs. 28.52 Gy, P=0.038), 107% isodose (V107%) of the PTV (2.43% vs. 3.74%, P=0.001), D100% of the hippocampus (9.31 Gy vs. 9.16 Gy, P=0.009), and the Dmean scalp (16.7 Gy vs. 16.8 Gy, p=0.035). The 10 MV FB and FFF beam plans showed significant differences in the conformity index (0.9 vs. 0.85, P=0.01), V107% of the PTV (1.68% vs. 4.54%, P=0.001), D100% (10.08 Gy vs. 9.81 Gy, P=0.036), and Dmean of the hippocampus (12.78 Gy vs. 12.57 Gy, P=0.018). The 6 MV and 10 MV FFF beams showed homogeneous conformal plans, which required 18-19% more MUs, compared to the FB plans.
The 6 MV and 10 MV FB and FFFB spared the hippocampus and the scalp with acceptable target coverage in WBRT cases.

This study compared a three-dimensional conformal radiation therapy (3D-CRT) with a recently implemented intensity modulation radiation therapy (IMRT) technique performed in the irradiation of lung cancer. The objective of this study is to demonstrate the dosimetric advantages of IMRT in target coverage, dose homogeneity, and reducing toxicity.

Depth point doses were compared as calculated by the Varian Eclipse treatment planning system (TPS) on virtual created patient and experimentally measured by thermoluminescence (TL) dosimetry. For treatment planning the same lesion of the real case with different volumes and structures contouring details were created on Rando anthropomorphic phantom computed tomography (CT) data. Dose measurement was performed by calibrated thermoluminescent detectors.

The difference between experimental TL measured doses and calculated doses in both techniques show mean values of ~3% (IMRT) and ~1% (3D-CRT) for high dose (>0.55Gy) and ~7% IMRT and 6.5% (3D-CRT) for low dose (<0.55Gy). All IMRT optimized plans improved the heart (-28.3%), the spinal cord (-25.3%), and the left lung (-41.55%) sparing significantly, compared to the 3D-CRT plans. The optimized dose-volume histograms, the dose covering indices, and the dose profile across heterogeneity interfaces showed a significant improvement in dose conformity by IMRT.

These findings demonstrate well that TL dosimetry when combined with suitable point dose measurement procedures can efficiently be used as an external and independent dose audit for the comparison between 3D-CRT and IMRT. IMRT with its dose-volume optimization algorithm can achieve a treatment plan quality in lung cancer radiotherapy unachievable by 3D-CRT.

The current study aimed to compare linear accelerator-based three-dimensional conformal radiotherapy (Linac-3DCRT) technique with different techniques of the Radixact-X9 for the treatment of craniospinal irradiation (CSI).

Following a retrospective design, 22 CSI patients (Medulloblastoma) treated with Linac-3DCRT using the Novalis-Tx unit were selected for analysis. For each patient plan, additional sets of plans were generated using Helical, Direct-3DCRT, and Direct-intensity-modulated radiotherapy (Direct-IMRT) techniques of the Radixact-X9 unit. The dose prescription for brain planning target volume (brain PTV) and spine PTV were 36 Gy in 20 fractions and kept the same for all techniques. Planning time, patient setup time, homogeneity index (HI), and different dose-volume parameters for both PTV and organs at risk (OARs) were evaluated for comparison.

The Radixact-X9-Helical technique can generate a plan in a more comparable and better manner in respect of maximum and minimum doses for most of the organs. The Radixact-X9-Helical technique resulted in better PTV homogeneity in comparison with Linac-3DCRT, Radixact-X9-Direct-3DCRT, and Radixact-X9-Direct-IMRT. The values of HI were 3.57±0.77, 17.37±1.44, 8.15±1.02, and 8.62±0.98, respectively.

Not only administration of the Radixact-X9-Helical treatment technique is easier, but also can generate a better homogeneous plan than other treatment techniques like 3DCRT and IMRT regarding different parameters for comparisons like dose-volume received by OARs, patient setup time, move isocenter, and many more. So it can be an integral part of the radiotherapy department, according to their clinical needs like shorter treatment time with good sparing of critical OARs.

Measurement of indoor radon concentration and its determining factors is crucial for improving public health and developing proper methods that can reduce indoor radon concentrations. This study aimed to measure the indoor radon concentration and to examine its variations in relation to variables, such as the construction materials, ventilation, and age of buildings.

Indoor radon concentrations were measured using solid-state nuclear track detectors (SSNTDs) during winter. Each detector was mounted 50-90 cm above the surface flooring of bedrooms and living rooms. After three months of exposure, the detectors were collected and transferred to a laboratory. They were then etched in 6.25 N NaOH solution in a bath at a constant temperature of 90°C for 240 minutes. Next, the detectors were washed with distilled water and dried. The alpha particle tracks were counted using an automatic alpha track counting system.

The mean radon concentration was 53.20 Bq/m3,and 94% of the samples had a radon concentration 3, which is the action level proposed by the World Health Organization (WHO). The annual effective dose varied from 0.25 mSvy-1 to 3.05 mSvy-1, with a mean dose of 0.91 mSvy-1. The results showed that the type of constructed materials and ventilation influence the indoor radon concentration in winter.

The annual effective dose in the study area was below the global average of 1.15 mSvy-1. Therefore, local residents must be informed about the health risks of high radon concentrations and understand the role of improved ventilation in reducing the indoor radon levels.

To study the effect of the International Atomic Energy Agency (IAEA) TRS-483 recommended beam quality correction factor in reference dosimetry and to examine the recommended field output correction factor for relative dosimetry of 6-MV flattening filter free (FFF) small fields, used in a Varian TrueBeam linear accelerator (LINAC).

The beam quality and field output correction for 6-MV FFF beams were adopted from the TRS-483 protocol. Monte Carlo (MC) simulation of the output factor was performed using the PENELOPE-based PRIMO software and compared with the TRS-483 corrected output factors. Two analytical anisotropic algorithm (AAA) models in the EclipseTM treatment planning system (TPS) were created; one with an output factor taken as the ratio of meter readings and one with an output factor obtained by multiplying the TRS-483 correction factor by the ratio of meter readings. Besides, box field and dynamic conformal arc (DCA) plans were created for both AAA models for verification and validation. The patient-specific quality assurances (QA) for ten different targets were performed, and deviations between the measured and TPS-calculated point doses in both models were examined.

Separate beam quality correction factors for FFF beams in the TRS-483 protocol only resulted in an improvement of 0.1% in reference dosimetry. The TRS-483 corrected output factor was in a better agreement with the MC-calculated output factor. For a patient-specific QA of DCA plans, the output factor-corrected AAA dose calculation algorithm showed a better agreement between the measured and simulated doses. Also, there was a smaller deviation (1.2%) for the smallest target of 0.23 cc (8 mm equivalent sphere diameter) used in this study.

The field output factors for the LINAC small beams can be improved by incorporating the TRS-483 correction factors. However, the extent of improvement that can be expected depends on the source model of the calculation algorithm and how these well-generalized corrections are suitable for user beams and detectors.

The 28-day rule is utilized as a precautionary measure for irradiating the fetus at an early stage of conception for abdominal and pelvic radiography. There is a probability of the women being pregnant if the 28-day rule is applied for this examination and thus irradiating the conceptus. It is difficult to convince people that low radiation doses during early pregnancy will not cause any harm to the conceptus. As such this study was to ascertain whether the 28-day rule can be used safely for abdominal radiography in women of reproductive age.

The experimental study was conducted at the Radiography Laboratory, International Islamic University Malaysia, Kuantan using an anthropomorphic PBU-50 phantom. The entrance surface dose (ESD), organ dose and effective dose (ED) were estimated using CALDose_X 5.0 software, based on the exposure parameters and tube output of the x-ray unit.

The mean ESD for AP abdominal radiographic examination of 3.162 mGy is within that recommended by radiation protection regulatory bodies. Additionally, the mean organ dose of 0.468 mGy is lower than the threshold value of 100 mSv for the “all-or-none” phenomenon to happen. Further, the mean ED of 0.73 mSv is within the recommendation of the International Atomic Energy Agency (IAEA) and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR).

This study indicated that the 28-day rule is safe to be used for abdominal radiography for a woman of reproductive age.

Most women with left-sided breast cancer are at an increased risk of heartmorbidity and mortality from the adjuvant radiotherapy due to an increase in heart absorbed dose during radiotherapy treatment. This study aimed to compare free-breathing intensity-modulated radiotherapy (FB-IMRT) and three-dimensional conformal deep inspiration breath-hold (3DCRT-DIBH) techniques in terms of the cardiac dose.

In total, 15 women with left-sided breast cancer underwent FB and DIBH computed tomography (CT) scans in the same supine position. For DIBH CT, 3D-CRT plans were created using two opposing wedged tangential fields and for FB-CT, 4-5 IMRT optimized tangential fields were created. All plans were evaluated using the dose-volume histogram. The data were analyzed in SPSS software version 20 (IBM, IL).

The FB-IMRT plans were more homogeneous and had more dose coverage and fewer hotspots, than the 3DCRT-DIBH plans; however, the planning target volume V95% was clinically acceptable for both techniques. Furthermore, the 3DCRT-DIBH plans were much faster and require fewer monitor units. A significantly lower mean dose of heart, left lung, left anterior descending coronary artery, right lung, and V10% left lung were observed in 3DCRT-DIBH plans, compared to FB-IMRT plans. Moreover, FB-IMRT plans showed a significant further dose reduction in heart V25% and V30%.

The majority of the patients with left-sided breast cancer who treated with the DIBH technique were getting sufficient benefits of radiotherapy, and DIBH was a comprehensive strategy for reducing cardiac doses during radiotherapy treatment.

The pituitary gland is frequently irradiated during radiation therapy of head and neck tumors which can influence the quality of life of the patients after radiation therapy. This study aimed to estimate the normal tissue complication probability (NTCP) for the pituitary gland in head and neck cancers using two radiobiological models.

53 patients including 20 cases with nasopharyngeal cancer and 33 cases with brain tumor were studied. The dosimetric properties of each plan including minimum, mean and maximum doses were extracted from the dose-volume histogram curve. For estimation of pituitary gland response for each patient, the BIOPLAN software was used to calculate NTCP by LKB model and Matlab software was applied to calculate NTCP by equivalent uniform dose   (EUD) model. Models’ parameters including TD50, , and‘a’ were extracted from a previous study of radiobiological modeling of pituitary gland response to radiation therapy. For statistical analysis, the T-test was used to compare two models.

The average mean doses of 30.42 and 51.29 (Gy) of the pituitary gland were obtained for nasopharyngeal and brain tumor patients, respectively. The average NTCPs of the pituitary gland for nasopharyngeal patients estimated by LKB and Log-logistic models were 3.84 and 3.91%, respectively. In brain tumors, the average NTCP was 16.33% for LKB and 16.41% for Log-logistic models. The results showed that the log-logistic and LKB models provided comparable results and no statistically significant difference (P-value< 0.05) was found between two models.

The NTCP results indicated that the average NTCP of the pituitary gland for nasopharyngeal patients was approximately four times lower than that of brain tumors. Finally, implementation of follow up studies and modeling investigations are recommended for accurate estimation of pituitary gland complications following radiation therapy.

The occupational safety of nuclear medicine staff working with radioactive iodine (131I) has always been a major concern in nuclear medicine. Since 131I is a volatile substance, it may enter the body during respiration and be absorbed by the thyroid gland of the hospital staff, causing major health problems. This study aimed to develop a simple method for determining the activity concentration of absorbed 131I in the thyroid gland of nuclear medicine staff, using a home-made anthropomorphic neck-thyroid phantom. For this purpose, 131I, with an activity of 370 kBq, was injected inside the thyroid glands of the phantom. The dose rate was measured by placing a portable detector on the thyroid gland at the surface of the neck phantom. The measurements were repeated for two months. Next, a calibration curve was drawn for iodine activity inside the thyroid versus dose rate at the neck surface. The calibration curve was then used to estimate the absorbed activity in the thyroid of the staff in one of the main hospitals of Shiraz, Iran. Finally, a new software program was developed for assessing and recording the activity concentration of 131I accumulated in the thyroid gland. Every day, the dose rate was measured by placing the detector on the neck of the staff. The dose rates were converted to activity concentrations inside the thyroid, using the mentioned calibration curve. The results indicate that using the calibration factors for every detector, one can have the estimate of the radio-Iodine activity inside the thyroid. The method proposed in this study can be applied for internal contamination determination in normal working conditions and in accidents.

To study the impact of 6 MV and 10 MV flattened beam (FB) and flattening filter free (FFF) beam in whole brain radiotherapy (WBRT) by using volumetric modulated arc therapy (VMAT). Twenty WBRTpatients were selected randomly. The dose prescription was 30 Gy, which was delivered in ten fractions. The planning target volume (PTV) and organs at risk (OARs) were contoured. Four VMAT plans, including 6 MV FB, 6 MV FFF, 10 MV FB, and 10 MV FFF beam plans, were generated. The 6MV FB and FFF beam plans were statistically significant (p <0.05) in terms of the dose received by 98% of the PTV (D98%) (26.86 Gy vs. 27.31 Gy, P=0.006), the dose received by 95% of the PTV (D95%) (28.28 Gy vs. 28.52 Gy, P=0.038), 107% isodose (V107%) of the PTV (2.43% vs. 3.74%, P=0.001), D100% of the hippocampus (9.31 Gy vs. 9.16 Gy, P=0.009), and the Dmean scalp (16.7 Gy vs. 16.8 Gy, p=0.035). The 10 MV FB and FFF beam plans showed significant differences in the conformity index (0.9 vs. 0.85, P=0.01), V107% of the PTV (1.68% vs. 4.54%, P=0.001), D100% (10.08 Gy vs. 9.81 Gy, P=0.036), and Dmean of the hippocampus (12.78 Gy vs. 12.57 Gy, P=0.018). The 6 MV and 10 MV FFF beams showed homogeneous conformal plans, which required 18-19% more MUs, compared to the FB plans. The 6 MV and 10 MV FB and FFFB spared the hippocampus and the scalp with acceptable target coverage in WBRT cases.