Evaluation of Eye Lens Dose Reduction Technics in Head CT

The purpose of this study is to find the best protocol to reduce the X-ray dose to the eye lens during head diagnostic computed tomography (CT) without decreasing image quality in the organs of interest according to the type of scanner. The lens of the eye is one of radiosensitive tissues in the body. Radiation induced cataract has been demonstrated among staff involved in interventional procedures using X-rays. This study compares the absorbed dose and image quality of several dose reduction technics to the eye lens during head CT exam namely bismuth shielding, organ-based dose modulation, tube current modulation, tube voltage modulation and the combination of a number of these techniques. Compared to the reference scan (Fixed tube current without bismuth shielding), the dose to the eye lens was reduced by 29.91% with bismuth shield, 14.55% with tube current modulation, 37.76% with tube current modulation and bismuth shield. The combination of organ-based dose modulation with tube voltage modulation reduced the dose by 44.93% that of tube current modulation with tube voltage modulation reduced by 19.03% and that of tube current modulation with tube voltage modulation and shield by 46.73%. The combination of organ-based dose with tube voltage modulation provided superior image quality than that of tube current modulation with tube voltage modulation and shield while similarly reducing dose to the eye lens.

Bismuth Pelvic X-Ray Shielding Reduces Radiation Dose Exposure in Pediatric Radiography

Background. Radiation using conventional X-ray is associated with exposure of radiosensitive organs and typically requires the use of protection. This study is aimed at evaluating the use of bismuth shielding for radiation protection in pediatric pelvic radiography. The effects of the anteroposterior and lateral bismuth shielding were verified by direct measurements at the anatomical position of the gonads. Methods. Radiation doses were measured using optically stimulated luminescence dosimeters (OSLD) and CIRS ATOM Dosimetry Verification Phantoms. Gonad radiographs were acquired using different shields of varying material (lead, bismuth) and thickness and were compared with radiographs obtained without shielding to examine the effects on image quality and optimal reduction of radiation dose. All images were evaluated separately by three pediatric orthopedic practitioners. Results. Results showed that conventional lead gonadal shielding reduces radiation doses by 67.45%, whereas dose reduction using one layer of bismuth shielding is 76.38%. The use of two layers of bismuth shielding reduces the dose by 84.01%. Using three and four layers of bismuth shielding reduces dose by 97.33% and 99.34%, respectively. Progressively lower radiation doses can be achieved by increasing the number of bismuth layers. Images obtained using both one and two layers of bismuth shielding provided adequate diagnostic information, but those obtained using three or four layers of bismuth shielding were inadequate for diagnosis. Conclusions. Bismuth shielding reduces radiation dose exposure providing appropriate protection for children undergoing pelvic radiography. The bismuth shielding material is lighter than lead, making pediatric patients more comfortable and less apt to move, thereby avoiding repeat radiography.

Assessment of Thyroid Cancer Risk After Cervical Computed Tomography: The Impact of Bismuth Shielding

Background: Computed tomography (CT) is vastly applied in X-ray procedures because of its high quality in detecting the anatomical structures of the body. However, it leads to an increase in patient dose, resulting in carcinogenesis. In the head and neck CT, the thyroid is the most important at-risk organ. The aim of this study was to estimate thyroid cancer risk in cervical CT with and without a bismuth shield. Materials and Methods: After obtaining permission from the authors, data related to the thyroid dose of patients undergoing cervical CT in the study by Santos et al (2019) were used, and then thyroid cancer risk was calculated for different ages at exposure in male and female patients using the biological effects of the ionizing radiation (BEIR) VII model. Results: Using bismuth shielding reduced thyroid dose by 37% and 39% in male and female phantoms, respectively. Thyroid cancer estimation demonstrated that the risk was nearly two-fold in females compared to males. Finally, bismuth shielding reduced 40% of cancer risk, and it decreased in both genders by increasing age at exposure. Conclusion: According to our findings, excess relative risk (ERR) up to 0.06% was associated with cervical CT. Although ERR amounts were low, the effect of radiation on thyroid cancer risk should not be neglected. Accordingly, it is suggested that future trials use bismuth shielding to reduce thyroid cancer risk.

Analysis of thyroid absorbed dose in cervical CT scan with the use of bismuth shielding

The Computed Tomography (CT) has become an important tool to diagnose cancer and to obtain additional information for different clinical questions. Today, it is a very fast, painless and noninvasive test that can be performed high quality images. However, CT scan usually requires a higher radiation exposure dose than a conventional radiography examination. The aim of this study is to determine the dose variation deposited in thyroid and in nearby radiosensitive organs, such as: lenses, pharynx, hypophysis, salivary gland and spinal cord with and without the use of bismuth shielded. A cervical CT scan was performed on anthropomorphic male phantom model Alderson Rando, using a GE scanner, Discovery model with 64 channels. Dose measurements have been performed by using radiochromic film strips to register the individual doses in the organs of interest. The results show us that the thyroid received the highest dose, 24.70 mGy, in the phantom, according to the incidence of the primary X-ray beam.

COMPARISON OF ORGAN-BASED TUBE CURRENT MODULATION AND BISMUTH SHIELDING IN CHEST CT: EFFECT ON THE IMAGE QUALITY AND THE PATIENT DOSE

The aim of the study was to compare the absorbed doses and image quality of organ-based tube current modulation (OBTCM) and bismuth shielding of breasts and thyroid against regular tube current modulation in chest CT scan. An anthropomorphic phantom and MOSFET dosemeters were used to evaluate absorbed doses. Image quality was assessed from HU and noise. Relative to the reference scan, the average absorbed dose reduction with OBTCM was 5.2% and with bismuth shields 24.2%. Difference in HU values compared to the reference varied between −4.1 and 4.2 HU in OBTCM scan and between −22.2 and 118.6 HU with bismuth shields. Image noise levels varied between 10.0 to 26.3 HU in the reference scan, from 9.6 to 27.7 HU for the OBTCM scan and from 11.9 to 43.9 HU in the bismuth scan. The use of bismuth shields provided greatest dose reduction compared to the investigated OBTCM.

Application of Different methods for Reducing Radiation Dose to Breast during MDCT

The increased use of computed tomography (CT) and its high radiation dose have led to great concerns about its potential for radiation induced cancer risks. Breast is a radiosensitive tissue based on tissue weighting factors assigned by the International Commission on Radiological Protection (ICRP). Moreover, the dose is maximal on the surface of the patient. Therefore, strategies should be taken to reduce radiation dose to the breast. The aim of this review is to introduce methods used for reducing radiation dose to breast in thoracic CT and review related performed studies. The literature indicates that bismuth shielding increases image noise and CT numbers as well as introducing streak artifacts. Tube current modulation (TCM) technique and iterative reconstruction algorithms can provide some levels of dose reduction to radiosensitive organs and superior image quality without the disadvantages of bismuth shielding. However, they are not available on all CT scanners, especially in low-income countries. Such centers may have to continue using bismuth shields to reduce the dose until these superior techniques become available at lower costs in all CT scanners. Furthermore, design and manufacture of new shields with the lower impact on image quality are desirable.

CT Thorax lavdose - En sammenligning av et organdosemodulerings program X-CARE og vismut beskyttelse

InnledningComputertomografi (CT) er en hyppig utført undersøkelse i Norge. Både mammae og thyroidea er strålefølsomme organer som eksponeres ved en CT thorax undersøkelse. For å få ned inngangsdosen (ESD) til slike strålefølsomme organer kan man enten benytte seg av en organspesifikk adaptiv dose reduksjons protokoll (X-CARE) eller isteden legge vismut beskyttelse over de strålefølsomme organene ved CT-undersøkelsen. I denne studien sammenligner vi huddosen (ESD) over mamma, samt bildekvalitet, ved bruk av disse to metodene ved en CT thorax lavdose undersøkelse?Material og metode30 spiral skanninger, hvorav ti standard lavdose, ti med vismut beskyttelse og ti med X-CARE, ble utført på et Alderson fantom, kombinert med Care Dose 4D, på en Siemens SOMATOM Definition Edge 128 CT maskin. ESD ble målt, CTDIvol og Dose-lengde-produkt (DLP) ble hentet ut fra doserapporten. Den objektive bildekvaliteten ble analysert, og vurdert ved hjelp av tre Region Of Interest (ROI), plassert hhv i luft, i lungeparenkymet og i pleura parietale. Signal til støyforhold (SNR) og kontrast til støyforhold (CNR) ble regnet ut ifra ROI verdiene.ResultaterESD til mamma viste dosereduksjon sammenlignet med en standard CT thorax lavdose; hhv 16,5 % dosereduksjon ved bruk av vismut beskyttelse, og 0,44 % ved X-CARE. Det var ingen forskjell i CTDIvol og DLP ved standard lavdose skanningen eller skanningen med vismut beskyttelse. Skanningen med X-CARE ga en økning i CTDIvol og DLP på omtrent 12 %. SNR og CNR i lungeparenkymet og pleura parietale var høyest ved standard lavdose undersøkelsen. Bildestøyen økte 48 % ved vismut og 26,4 % ved X-CARE.KonklusjonESD ble markant redusert ved CT thorax lavdose undersøkelsen med vismut beskyttelse, men ga samtidig en markant økning i bildestøyen. X-CARE reduserte ESD minimalt sammenlignet med standard lavdose skanningen, men ga økt bildestøy. Den mest effektive måten å oppnå en optimal lavdose undersøkelse på, er ved å utføre en standard CT thorax lavdose protokoll. AbstractIntroductionComputed tomography (CT) is a frequent examination conducted in Norway. Mammae and thyroid gland are both dose sensitive body organs, which are being exposed during a thoracic CT examination. Therefore, an optimization of protocols is necessary and X-CARE (organ-based tube current modulation) or bismuth protection may be applied during a CT examination. Will the two methods give a difference in the entrance surface dose (ESD) to mamma and the image quality of a low-dose thoracic CT examination?Materials and methodsThirty spiral CT scans of which ten was standard low-dose, ten with bismuth shielding and ten with X-CARE was performed on an Alderson phantom, combined with CARE Dose 4D and carried out on a Siemens SOMATOM Definition Edge 128. Measures as ESD, CTDIvol and Dose-length-product (DLP) were obtained from the dose report. The image quality was analysed objectively and assessed using three Region of Interest (ROI), placed in air, lung parenchyma and parietal pleura. Signal to noise ratio (SNR) and contrast to noise ratio (CNR) were calculated from the ROI results.ResultsESD to the mammary gland demonstrated a dose reduction compared to a standard thoracic CT low dose. Respectively; 16.5 % dose reduction with bismuth shielding and 0.44 % with X-CARE. There was no difference in CTDIvol and DLP between the standard low-dose scans and the scans with bismuth shielding. The CT scans with X-CARE gave an increase in CTDIvol and DLP by approximately 12 %. SNR and CNR in the lung parenchyma and parietal pleura were highest during the standard low-dose scans. Bismuth shielding increased the noise with 48 % and X-CARE with 26,4 %.ConclusionESD was significantly reduced during the CT thoracic low-dose examination using bismuth shielding, however notably the bismut increased the image noise. X-CARE reduced the ESD minimally compared to the CT low-dose scans, and it also increased the image noise. The most efficient way to achieve an optimal thoracic CT examination is to use a standard low-dose protoco