Distribution of natural and anthropogenic radionuclides and associated radiation indices in the Southwestern coastline of Caspian Sea

The distribution pattern of natural radionuclides (²²⁶Ra, ²³²Th, and ⁴⁰K) and anthropogenic radionuclide (¹³⁷Cs) in surface sediment samples from the southwestern coastline of the Caspian Sea were determined to estimate the radiation hazard indices using a high-purity germanium HPGe gamma-ray detector. The activity concentrations of the sediment samples ranged from 22.5 ± 1.0 to 47.4 ± 2.2 Bq kg^-1 dry weight (dw) for ²²⁶Ra, 6.5 ± 0.1 to 18.7 ± 0.7 Bq kg^-1 dw for ²³²Th, 559.9 ± 30.9 to 233.2 ± 19.4 Bq kg^-1 dw for ⁴⁰K, and 0.9 MDL (minimum detection limit) to 2.7 ± 0.1 Bq kg^-1 dw for ¹³⁷Cs. Based on the measured values, radiological risk indices were estimated. The mean values for absorbed dose rate, ambient dose equivalent rate, and excess lifetime cancer risk, were calculated as 35.7 nGy h^-1, 47.9 nSv h^-1, and 0.2, respectively.

WINDCATCHER VENTILATION COMPUTATION AND INDOOR 222RN CONCENTRATION IN TRADITIONAL ADOBE HOUSES

Radon-based radiation is a significant issue that can affect resident health as a contributory source of natural radiation from soil construction materials. This study investigates the effect of windcatchers on radon activity concentrations and radon exhalation rate from the soil surface in traditional adobe houses of Yazd, Iran. Radon concentrations were measured by passive detectors in 16 adobe houses. Computational fluid dynamics simulations were performed for different wind speed to calculate ventilation rate. The concentrations of 222Rn were in the ranges of 22 ± 1-117 ± 8 Bq m-3 with an average value of 50 ± 3 Bq m-3. The radon exhalation rates values were in the range of 8.3 ± 0.1 to 47.2 ± 0.5 Bq m-2 h-1. Radon concentration results in only one dwelling site were higher than the level recommended by the World Health Organization. The annual radon inhalation dose was found in seven sites higher than the worldwide average.

Evaluation of the ability of three commercially available dosimeters to detect systematic delivery errors in step-and-shoot IMRT plans

Background

There is limited data on error detectability for step-and-shoot intensity modulated radiotherapy (sIMRT) plans, despite significant work on dynamic methods. However, sIMRT treatments have an ongoing role in clinical practice. This study aimed to evaluate variations in the sensitivity of three patient-specific quality assurance (QA) devices to systematic delivery errors in sIMRT plans.

Materials and methods

Four clinical sIMRT plans (prostate and head and neck) were edited to introduce errors in: Multi-Leaf Collimator (MLC) position (increasing field size, leaf pairs offset (1-3 mm) in opposite directions; and field shift, all leaves offset (1-3 mm) in one direction); collimator rotation (1-3 degrees) and gantry rotation (0.5-2 degrees). The total dose for each plan was measured using an ArcCHECK diode array. Each field, excluding those with gantry offsets, was also measured using an Electronic Portal Imager and a MatriXX Evolution 2D ionisation chamber array. 132 plans (858 fields) were delivered, producing 572 measured dose distributions. Measured doses were compared to calculated doses for the no-error plan using Gamma analysis with 3%/3 mm, 3%/2 mm, and 2%/2 mm criteria (1716 analyses).

Results

Generally, pass rates decreased with increasing errors and/or stricter gamma criteria. Pass rate variations with detector and plan type were also observed. For a 3%/3 mm gamma criteria, none of the devices could reliably detect 1 mm MLC position errors or 1 degree collimator rotation errors.

Conclusions

This work has highlighted the need to adapt QA based on treatment plan type and the need for detector specific assessment criteria to detect clinically significant errors.

Gamma-Ray Protection Properties of Bismuth-Silicate Glasses against Some Diagnostic Nuclear Medicine Radioisotopes: A Comprehensive Study

This study aimed to perform an investigation for the potential implementation of bismuth silicate glasses as novel shield equipment instead of ordinary shields in nuclear medicine facilities. Accordingly, a group of Bi₂O₃ reinforced silicate glass system were investigated and compared with ordinary shields in terms of their gamma-ray attenuation properties in diagnostic nuclear medicine radioisotope energies emitted from ^99mTc, ¹¹¹In, ⁶⁷Ga, ¹²³I, ¹³¹I, ^81mKr, ²⁰¹Tl, ¹³³Xe. Mass attenuation coefficient (μm) results for glass samples were calculated comparatively with the XCOM program and MCNPX code. The gamma-ray attenuation parameters such as half value layer (HVL), tenth value layer (TVL), mean free path (MFP), effective atomic number (Z_eff) were obtained in the diagnostic gamma ray energy range from 75 to 336 keV. To confirm the attenuation performance of superior sample, obtained results were extensively compared with ordinary shielding materials. According to the results obtained, BISI6 glass sample with the highest Bi₂O₃ additive has an excellent gamma-ray protection.

Quality Assurance of Personal Radiation Shield for Kilovoltage Photon: A Multicentre Experience

Purpose

To optimize the maintenance of radiation shields, this study aims to analyze annual inspection files to assess the integrity of radiation shields and their associated factors with regard to defects in radiation shields in clinical settings.

Methods

A multicenter cross-sectional study was conducted at hospitals in Saudi Arabia. The data from annual inspection files of 1019 clinical lead radiation shields were analyzed. The factors of shield shape, unit where a shield is used, shield thickness, short-term use and number of users were examined. In addition to the inspection file analysis, radiation attenuation measurements were obtained for a subset of shields to compare newly purchased shields with older shields. Statistical analyses were performed using Fisher's exact test and a t-test.

Results

The results show that the highest percentage of failing shields were found in the emergency unit, fluoroscopy unit and operation room with a failure of approximately 7.14%, 5.61%, and 3.98%, respectively, of these shields. Fluoroscopy and operation room units were statistically significantly associated with shield defects. There was no association between shield damage and shape of shield, shield thickness, short-term use or number of users. Radiation attenuation measurements were similar for new and older shields.

Conclusion

As fluoroscopy units and operating rooms have a higher percentage of damaged shields, it is recommended that the shields employed in these units should be regularly inspected more frequently than once a year. The study highlights that the shields' age, transmission measurements that confirm that the correct shields are purchased according to the required kVp, physical appearance, and cleanliness should be recorded in annual inspection files. This study highlights the need for uniform inspection files of radiation shields across hospitals. National and international organizations may apply these findings to develop appropriate recommendations.

A simple and efficient method to measure beam attenuation through a radiotherapy treatment couch and immobilization devices

We propose a simple and efficient method to measure beam attenuation in one or two dimensions using an amorphous silicon electronic portal imaging device (a-Si EPID). The proposed method was validated against ionization chamber measurements. Beam attenuation through treatment couches (Varian Medical Systems) and immobilization devices (CIVCO Radiotherapy, USA) was examined. The dependency of beam attenuation on field size, photon energy, thickness of the couch, and the presence of a phantom were studied. Attenuation images were derived by computing the percentage difference between images obtained without and with a couch or immobilization devices determining the percentage of attenuation at the center and the mean attenuation. The beam attenuation measurements obtained with an a-Si EPID and an ionization chamber agreed to within ± 0.10 to 1.80%. No difference was noted between the center and mean of an attenuated image for a small field size of 5 × 5 cm², whereas a large field size of 15 × 15 cm² exhibited differences of up to 1.13%. For an 18 MV beam, the a-Si EPID required additional build-up material for accurate assessment of beam attenuation. The a-Si EPID could measure differences in beam attenuation through an image guided radiotherapy (IGRT) couch regardless of the variabilities in couch thickness. Interestingly, the addition of a phantom reduced the magnitude of attenuation by approximately 1.20% for a field size of 15 × 15 cm². A simple method is proposed that provides the user with beam attenuation data in either 2D or 1D within a few minutes.

The Influence of Acquisition Mode on the Dosimetric Performance of an Amorphous Silicon Electronic Portal Imaging Device

AIMS

This study investigates the impact of cine acquisition mode on the dosimetric characteristics of a Varian aS500 amorphous silicon electronic portal imaging device (a-Si EPID).

MATERIALS AND METHODS

The performance of an a-Si EPID operated in cine mode was assessed and compared to its performance when operated in an integrated mode and dose measurements using an ionization chamber. This study was conducted at different photon energies and the EPID performance was assessed as function of the delivered dose, dose rate, multileaf collimator speed, field size, phantom thickness, and intensity-modulated radiation therapy fields.

RESULTS

The worst nonlinearity was observed at low monitor unit (MU) settings < 100 MU with the highest dose per frame. The nonlinearity of response at a low MU setting was attributed due to the loss of four cine images during each delivery. The EPID response with changing dose rate for 10 MU delivered had similar results to its performance in an integrated mode and ionization chamber. Despite the nonlinearity of response with low MU delivered, EPID performance operated in cine and integrated acquisition modes had comparable responses within 2%.

CONCLUSIONS

For EPID dosimetry application using cine mode, this study recommends the calibration of the EPID images to be undertaken at a large MU. There were no additional corrections that were required when the EPID operated in cine acquisition mode as compared to calibration in integrated mode.