CT acquisition parameter selection in the real world: impacts on radiation dose and variation amongst 155 institutions.

OBJECTIVE: Quantify the relationship between CT acquisition parameters and radiation dose, how often parameters are adjusted in real-world practice, and their degree of contribution to real-world dose distribution. Identify discrepancies between parameters that are impactful in theory and impactful in practice. METHODS: This study analyses 1.3 million consecutive adult routine abdomen exams performed between November 2015 and Jan 2021 included in the University of California, San Francisco International CT Dose Registry of 155 institutions. We calculated geometric standard deviation (gSD) for five parameters (kV, mAs, spiral pitch, number of phases, scan length) to assess variation in practice. A Gaussian mixed regression model was performed to predict the radiation dose-length product (DLP) using the parameters. Three conceptualizations of "impact" were computed for each parameter. To reflect the theoretical impact, we predict the increase in DLP per 10% (and 15%) increase in the parameter. To reflect the real-world practical impact, we predict the increase in DLP per gSD increase in the parameter. RESULTS: Among studied examinations, mAs, number of phases, and scan length were frequently manipulated (gSD 1.52-1.70); kV was rarely manipulated (gSD 1.07). Theoretically, kV is the most impactful parameter (29% increase in DLP per 10% increase in kV, versus 5-9% increase for other parameters). In real-world practice, kV is less impactful; for each gSD increase in kV, the DLP increases by 20%, versus 22-69% for other parameters. CONCLUSION: Despite the potential impact of kV on radiation dose, this parameter is rarely manipulated in common practice and this potential remains untapped. CLINICAL RELEVANCE STATEMENT: CT beam energy (kV) modulation has the potential to strongly reduce radiation over-dosage to the patient, theoretically more so than similar degrees of modulation in other CT acquisition parameters. Despite this, beam energy modulation rarely occurs in practice, leaving its potential untapped. KEY POINTS: • The relationship between CT acquisition parameter selection and radiation dose roughly coincided with established theoretical understanding. • CT acquisition parameters differ from each other in frequency and magnitude of manipulation, with beam energy (kV) being rarely manipulated. • Beam energy (kV) has the potential to substantially impact radiation dose, but because it is rarely manipulated, it is the least impactful CT acquisition parameter affecting radiation dose in practice.

A time-resolved clonogenic assay for improved cell survival and RBE measurements.

Purpose: The in vitro clonogenic assay (IVCA) is the mainstay of quantitative radiobiology. Here, we investigate the benefit of a time-resolved IVCA version (trIVCA) to improve the quantification of clonogenic survival and relative biological effectiveness (RBE) by analyzing cell colony growth behavior. Materials & Methods: In the IVCA, clonogenicity classification of cell colonies is performed based on a fixed colony size threshold after incubation. In contrast, using trIVCA, we acquire time-lapse microscopy images during incubation and track the growth of each colony using neural-net-based image segmentation. Attributes of the resulting growth curves are then used as predictors for a decision tree classifier to determine clonogenicity of each colony. The method was applied to three cell lines, each irradiated with 250 kV X-rays in the range 0-8 Gy and carbon ions of high LET (100 keV/µm, dose-averaged) in the range 0-2 Gy. We compared the cell survival curves determined by trIVCA to those from the classical IVCA across different size thresholds and incubation times. Further, we investigated the impact of the assaying method on RBE determination. Results: Size distributions of abortive and clonogenic colonies overlap consistently, rendering perfect separation via size threshold unfeasible at any readout time. This effect is dose-dependent, systematically inflating the steepness and curvature of cell survival curves. Consequently, resulting cell survival estimates show variability between 3% and 105%. This uncertainty propagates into RBE calculation with variability between 8% and 25% at 2 Gy.Determining clonogenicity based on growth curves has an accuracy of 95% on average. Conclusion: The IVCA suffers from substantial uncertainty caused by the overlap of size distributions of delayed abortive and clonogenic colonies. This impairs precise quantification of cell survival and RBE. By considering colony growth over time, our method improves assaying clonogenicity.

Evaluation of Dose-Painting in the Dominant Intraprostatic Lesions by Radiobiological Parameters using 68Ga- PSMA PET/CT.

Background: Patients diagnosed with dominant intraprostatic lesions (DIL) may need radiation doses over than 80 Gy. Dose-painting by contours (DPC) is a useful technique which helps the patients. Dose-painting approach need to be evaluated. Objective: To evaluate the DCP technique in the case of boosting the DILs by radiobiological parameters, tumor control probability (TCP), and normal tissue complication probability (NTCP) via PET/CT images traced by 68Ga-PSMA. Material and Methods: In this analytical study, 68Ga-PSMA PET/CT images were obtained from patients with DILs that were delineated using the Fuzzy c-mean (FCM) algorithm and thresholding methods. The protocol of therapy included two phases; at the first phase (ph1), a total dose of 72 Gy in 36 fractions were delivered to the planning target volume (PTV1); the seconds phase consisted of the application of variable doses to the PTV2. Moreover, two concepts were also considered to calculate the TCP using the Zaider-Minerbo model. Results: The lowest volume in DILs belonged to the DIL1 extracted by the FCM method. According to dose-volume parameters of the rectum and bladder, by the increase in the PTV dose higher than 92 Gy, the amounts of rectum and bladder doses are increased. There was no difference between the TCPs of DILs at doses higher than 86 Gy and 100 Gy for ordinary and high clone density, respectively. Conclusion: Consequently, our dose-painting approach for DILs, extracted by the FCM method via PET/CT images, can reduce the total dose for prostate radiation with 100% tumor control and less normal tissue complications.

Impact of Low-Dose Computed Tomography on Computed Tomography Orders and Scan Length.

Background: New techniques have reduced the radiation dose delivered from a computed tomography (CT) examination. These techniques do not affect the number of scans ordered, the number of phases in each examination, or the scan length, as these parameters are controlled by ordering providers and CT technologists. The purpose of this study was to determine if deploying low-dose CT resulted in an increase in radiation exposure because of more liberal ordering habits or more liberal scanning ranges. Methods: We identified the most frequent CT examination types through a retrospective study of billing data from 2013. A campaign for low-dose CT scans was implemented, and data from 2 months prior and 2 months after were collected (n=797; average age=51.0 years ± 20.5; range, 4 to 97 years) and analyzed for differences in radiation dose, overall area scanned, and number of phases requested using unpaired t tests. Results: According to the billing data, the largest category of CT scans was the abdominal CT (31% of all CT examinations). After the low-dose campaign was implemented, we observed no difference in the number of examination phases ordered (1.2 ± 0.5 vs 1.3 ± 0.6, P=0.15), no increase in length of the scan (45.1 ± 7.5 cm vs 43.7 ± 10. 4 cm, P=0.08), and an overall decrease in dose (1,069 ± 634 mGy*cm vs 676 ± 480 mGy*cm, P<0.001). Conclusion: A campaign alerting staff to the availability of low-dose CT did not cause an increase in CT examination ordering and did not impact the area scanned by technologists.

Volume effects of radiotherapy on the risk of second primary cancers: A systematic review of clinical and epidemiological studies.

As modern radiotherapy, including intensity-modulated techniques, is associated with high dose gradients to normal tissues and large low-to-moderate dose volumes, the assessment of second primary cancer (SPC) risks requires quantification of dose-volume effects. We conducted a systematic review of clinical and epidemiological studies investigating the effect of the irradiated volume or dose-volume distribution to the remaining volume at risk (RVR) on SPC incidence. We identified eighteen studies comparing SPC risks according to the irradiated volume (i.e., in most studies, the size or number of fields used), and four studies reporting risk estimates according to the dose distribution to the RVR (after whole-body dose reconstruction). An increased risk of SPCs (mainly breast and lung cancers) with extended radiotherapy was observed among patients treated for Hodgkin lymphoma or childhood cancers. However, normal tissue dose distribution was not estimated, limiting the interpretation of those results in terms of volume effects on organs at risk. Studies considering whole-body exposures quantified dose-response relationships for point dose estimates, without accounting for dose-volume distributions. Therefore, they disregarded possible tissue effects (e.g. bystander and abscopal effects, stem cell repopulation) which may play a role in the induction of SPCs. Currently, there is no clinical or epidemiological information about a possible role of high dose gradients in surrounding organs, or increasing volumes of distant tissues exposed to low doses, in the risk of SPCs. Opportunities for future research nevertheless now exist, since methods and tools for estimating individual whole-body dose-volume distributions in large patient populations have been developed.

Inclusion of dosimetric data as covariates in toxicity-related radiogenomic studies : A systematic review.

PURPOSE: This systematic review evaluates the completeness of dosimetric features and their inclusion as covariates in genetic-toxicity association studies. MATERIALS AND METHODS: Original research studies associating genetic features and normal tissue complications following radiotherapy were identified from PubMed. The use of dosimetric data was determined by mining the statement of prescription dose, dose fractionation, target volume selection or arrangement and dose distribution. The consideration of the dosimetric data as covariates was based on the statement mentioned in the statistical analysis section. The significance of these covariates was extracted from the results section. Descriptive analyses were performed to determine their completeness and inclusion as covariates. RESULTS: A total of 174 studies were found to satisfy the inclusion criteria. Studies published ≥2010 showed increased use of dose distribution information (p = 0.07). 33% of studies did not include any dose features in the analysis of gene-toxicity associations. Only 29% included dose distribution features as covariates and reported the results. 59% of studies which included dose distribution features found significant associations to toxicity. CONCLUSION: A large proportion of studies on the correlation of genetic markers with radiotherapy-related side effects considered no dosimetric parameters. Significance of dose distribution features was found in more than half of the studies including these features, emphasizing their importance. Completeness of radiation-specific clinical data may have increased in recent years which may improve gene-toxicity association studies.

Constrictive Pericarditis 5 Months after Radiation Therapy in a 62-Year-Old Woman with Esophageal Cancer.

Most pericardial changes appear within a few weeks in patients who have undergone radiation therapy for thoracic neoplasms. Chronic pericardial constriction typically occurs decades later, consequent to fibrosis. Early constrictive pericarditis after chest irradiation is quite rare. We report the case of a 62-year-old woman who underwent radiation therapy for esophageal cancer and presented with constrictive pericarditis 5 months later. We searched the English-language medical literature from January 1986 through December 2015 for reports of early constrictive pericarditis after irradiation for thoracic malignancies. We defined "early" as a diagnosis within one year after radiation therapy. Five cases fit our criteria, and we summarize the findings here. To our knowledge, ours is the first definitive report of a patient with esophageal cancer to present with early radiation-induced constrictive pericarditis. We conclude that constrictive pericarditis can occur early after radiation for thoracic malignancies, albeit rarely. When planning care for cancer patients, awareness of this sequela is helpful.

Radiotherapy in desmoid tumors : Treatment response, local control, and analysis of local failures.

BACKGROUND: Desmoid tumors (aggressive fibromatosis) are rare soft tissue tumors which frequently recur after surgery. Desmoid tumors arise from musculoaponeurotic tissue in the extremities, head and neck, abdominal wall, or intra-abdominally. Our aim was to examine the outcome of radiotherapy of desmoid tumors in a single institution series. PATIENTS AND METHODS: We evaluated 41 patients with desmoid tumors treated with 49 radiotherapies between 1987 and 2012. Radiologic images for response evaluation were reassessed and responses to treatment registered according to RECIST criteria 1.1. For patients with local failures radiation dose distribution was determined in each local failure volume using image co-registration. Recurrences were classified as in-target, marginal, or out-of-target. Prognostic factors for radiotherapy treatment failure were evaluated. RESULTS: Radiotherapy doses varied from 20-63 Gy (median 50 Gy) with a median fraction size of 2 Gy. The objective response rate to definitive radiotherapy was 55% (12/22 patients). Median time to response was 14 months. A statistically significant dose-response relation for definitive and postoperative radiotherapy was observed both in univariate (p-value 0.002) and in multivariate analysis (p-value 0.02) adjusted for potential confounding factors. Surgery before radiotherapy or surgical margin had no significant effect on time to progression. Nine of 11 (82%) local failures were classified as marginal and two of 11 (18%) in-target. None of the recurrences occurred totally out-of-target. CONCLUSIONS: Radiotherapy is a valuable option for treating desmoid tumors. Radiotherapy dose appears to be significantly associated to local control.

A Questionnaire Cross-Sectional Study on Application of CBCT in Dental Postgraduate Students.

BACKGROUND: CBCT is a new emerging imaging technique which uses a cone-shaped radiation beam that is centered on a 2D detector. It is now routinely evaluated for oral and para-oral disorders. It has been widely accepted in practice in radiology in academic and hospital settings and included in the curricula of some countries. The present study aimed to evaluate the awareness of and knowledge on CBCT among postgraduates. MATERIAL/METHODS: After obtaining permission and ethical clearance from concerned authorities, an anonymous survey on CBCT was conducted in a dental college by using a close-ended validated questionnaire to get to know the knowledge on CBCT among postgraduates in a dental college in India. RESULTS: A total of 100 volunteers participated but only 88 postgraduates responded to the questionnaire. Among the respondents, 54.5% were not using CBCT for diagnostic purposes at their work place. A total of 68.2% of respondents were partially aware of common terminologies used in CBCT. Most of the respondents were unsure about radiation exposure of CBCT when compared to other types of imaging. Almost nobody had any idea on relative importance of image characteristics. Only half of the respondents were willing to attend a hands-on course on CBCT interpretations versus pathology. CONCLUSIONS: In the present study it was apparent that most of the respondents were lacking adequate knowledge on CBCT. Hence, there is an urgent need for more training programs on CBCT which would result in better diagnosis and treatment planning.

Radiation-induced mesothelioma among long-term solid cancer survivors: a longitudinal analysis of SEER database.

We investigated the association between external beam radiotherapy (EBRT) and pleural and peritoneal mesothelioma among long-term (>5 years) solid cancer survivors. We analyzed data from the US Surveillance, Epidemiology, and End Results (SEER) program (1973-2012). We fitted survival models adjusted by age, gender, race, year, surgery, and relative risk of primary mesothelioma in the county of residence (proxy for individual asbestos exposure). We estimated hazard ratios [HR] with reference to nonirradiated patients. We distinguished between scattered and direct irradiation to study the dose-response. We observed 301 mesotheliomas (265 pleural; 32 peritoneal; 4 others) among 935,637 patients. EBRT increased the risk of mesothelioma (any site; HR 1.34, 95% CI 1.04-1.77). We observed an increased risk of pleural mesothelioma (HR for EBRT 1.34, 95% CI 1.01-1.77), but we did not find signs of a dose-response relationship (HR for scattered irradiation 1.38; HR for direct irradiation 1.23). On the opposite, only direct peritoneal irradiation was associated with peritoneal mesothelioma (HR 2.20, 95% CI 0.99-4.88), particularly for latencies ≥10 years (HR 3.28, 95% CI 1.14-9.43). A competing risks analysis revealed that the clinical impact of radiation-induced mesothelioma was limited by the high frequency of competing events. The cumulative incidence function of mesothelioma after 40 years of observation was very low (nonirradiated patients 0.00032, irradiated patients 0.00055).EBRT might be a determinant of mesothelioma. Longer latency periods are associated with higher risks, while the dose-response seems nonlinear. The clinical impact of mesothelioma after EBRT for primary solid cancers is limited.

Reconstruction of paediatric organ doses from axial CT scans performed in the 1990s - range of doses as input to uncertainty estimates.

OBJECTIVE: To assess the range of doses in paediatric CT scans conducted in the 1990s in Norway as input to an international epidemiology study: the EPI-CT study, http://epi-ct.iarc.fr/ . METHODS: National Cancer Institute dosimetry system for Computed Tomography (NCICT) program based on pre-calculated organ dose conversion coefficients was used to convert CT Dose Index to organ doses in paediatric CT in the 1990s. Protocols reported from local hospitals in a previous Norwegian CT survey were used as input, presuming these were used without optimization for paediatric patients. RESULTS: Large variations in doses between different scanner models and local scan parameter settings are demonstrated. Small children will receive a factor of 2-3 times higher doses compared with adults if the protocols are not optimized for them. For common CT examinations, the doses to the active bone marrow, breast tissue and brain may have exceeded 30 mGy, 60 mGy and 100 mGy respectively, for the youngest children in the 1990s. CONCLUSIONS: The doses children received from non-optimised CT examinations during the 1990s are of such magnitude that they may provide statistically significant effects in the EPI-CT study, but probably do not reflect current practice. KEY POINTS: • Some organ doses from paediatric CT in the 1990s may have exceeded 100 mGy. • Small children may have received doses 2-3 times higher compared with adults. • Different scanner models varied by a factor of 2-3 in dose to patients. • Different local scan parameter settings gave dose variations of a factor 2-3. • Modern CTs and age-adjusted protocols will give much lower paediatric doses.

Knowing the Enemy: Health Care Provider Knowledge of Computed Tomography Radiation Dose and Associated Risks.

BACKGROUND: There is ionizing radiation and associated risk from many medical imaging examinations, especially computed tomography (CT). Unfortunately, health care providers often have limited knowledge regarding radiation dose levels and potential risk. RESEARCH OBJECTIVES: To assess knowledge of dose levels and risk among referring physicians, imaging technologists, and radiologists in Saskatoon, Saskatchewan, and to identify potential differences between and within those groups. MATERIALS AND METHODS: A survey was designed and administered to health care professionals. RESULTS: A total of 308 of 328 surveys were completed (91% response rate). Overall 73% of physicians, 97% of radiologists, and 76% of technologists correctly believed that there is a risk for cancer from an abdomen-pelvic CT scan. Although only 18% of physicians, 28% of radiologists, and 22% of technologists selected the most appropriate estimate of abdominal-pelvic CT dose in terms of chest x-ray equivalents, this is similar to other reported studies. Physicians and technologists who use CT were more likely to select the correct dose than those who do not. Most respondents (91% of physicians, 100% of radiologists, and 100% of technologists) felt that pregnant patients should always be informed about radiation dose as a risk. Although frequency of discussing risk decreased with increasing patient age, technologists were more likely to discuss risk at any age. A total of 93% of respondents expressed interest in receiving dose feedback from medical imaging procedures. CONCLUSIONS: Radiologists and technologists generally showed better knowledge than referring physicians. Among physicians and technologists, knowledge was better in those who use CT than those who do not.

Iterative reconstruction improves imaging quality of low er -radiation CT perfusion in patients w ith acute ischemic stroke / 国际脑血管病杂志

Objective To investigate w hether the iterative reconstruction (iDose 4 ) technique improves imaging quality of the low-radiation-dose w hole brain CT perfusion (CTP). Methods Thirty-five consecutive patients w ith clinical y suspected ischemic stroke w ere col ected. Bril iance 256 iCT w as used to perform low-radiation-dose w hole brain CTP, and the filtered back projection (FBP) and iDose 4 algorithm w ere used to conduct image reconstruction. The noise and signal to noise ratio of the 2 kinds of reconstruction algorithms, as w el as the imaging quality of each parameter map w ere compared. Results The effective dose of the w hole brain CTP w as 2.2 mSv. Compared w ith FBP, the noise of each region of interest in the iDose4 Tmax map was decreased significantly ( P<0.05) and the signal to noise ratio was increased significantly (P<0.05). The imaging quality scores (median, interquartile range) reconstructed by FPB group w ere significantly low er than by iDose 4 for cerebral blood flow (CBF) map ( 5.00 [3.00-6.00]vs. 6.00 [5.00-6.00]; Z= -2.784, P=0.005), cerebral blood volume (CBV) map ( 6.00 [5.00-6.00] vs. 6.00 [6.00-7.00]; Z= -3.674, P<0.001), and mean transit time (MTT) map (4.00 [3.00-5.00] vs. 5.00 [4.00-6.00]; Z=3.394, P=0.001). The proportions of the poor quality in CBF map ( 34.3%vs. 11.4%;χ2 =7.036, P=0.030), CBV map (11.4%vs.2.9%; χ2 =7.485, P=0.024 ) and MTT map (28.6%vs.11.4%;χ2 =5.318, P=0.070) reconstructed by FBP w ere significantly higher than by iDose 4 . Conclusions The iDose4 technique may improve imaging quality of low er-radiation-dose CTP.

Avaliação dos efeitos da radiação em procedimentos intervencionistas cardíacos / Evaluation of the effects of radiaton on cardiac interventional procedures

Objetivo - Procedimento intervencionista cardíaco é uma modalidade de exame que através de imagens em tempo real, o médico pode intervir sem que o paciente seja submetido a procedimentos cirúrgicos e riscos pós-operatórios. Esses procedimentos podem resultar em efeitos determinísticos e estocásticos para os profissionais que os realizam. O objetivo deste estudo foi avaliar se há indicativos dos efeitos causados pela radiação nos profissionais ocupacionais de uma instituição de saúde da cidade de São Paulo. Métodos - Foram analisados os dosímetros e hemogramas de dois profissionais. Resultados - As doses encontradas nos dosímetros dos dois profissionais foram 32,4 e 36,6 mSv e pequena variação nos componentes sanguíneos na análise dos hemogramas. Conclusão - Não houve indicativos de alteração causados por radiação ionizante nos profissionais analisados.

Objective - Cardiac interventional procedure is a type of exam that through real-time imaging, the physician can intervene without the patient to undergo surgical procedures and postoperative risks. These procedures can result in deterministic and stochastic effects for the professionals who perform them. The aim of this study is to assess whether there is evidence of the effects caused by radiation in a professional occupational health institution in São Paulo city. Methods - Dosimeters were analyzed and peripheral blood of two professionals. Results - Doses found in dosimeters of the two professionals were 32.4 and 36.6 mSv and a small variation in the blood components in the analysis of blood counts. Conclusion - There were no indications of change caused by ionizing radiation in occupational analyzed.

Dose-effect relationship between Q-switch ruby laser and skin pigmentation in Guinea pigs / 中华皮肤科杂志

Objective To investigate the dose-effect relationship between Q-switch ruby laser and skin pigmentation in Guinea pigs. Methods Ten Guinea pigs were included in this study, and the back of each pig was divided into 5 areas, negative control area receiving no UVB irradiation or laser treatment, positive control area receiving UVB irradiation but no laser treatment, low-, middle- and high-dose areas receiving UVB irradiation followed by the treatment with laser at an energy density of 1.5, 3.0 and 6.0 J/cm2 for 4, 2, and 1 session, respectively, with an interval of 1 week. Melanin content index (MCI) was determined, and confocal laser scanning microscopy (CLSM) and histopathology were performed to observe melanin granules and melanocytes in the skin tissue from Guinea pigs before the initial laser treatment, 2 and 4 weeks after the final laser treatment. Results The best response was observed in the low-dose areas, and there was a complete clearance of hyperpigmentation in these areas, which maintained 8 weeks without recurrence, while different degrees of skin pigmentation recurred in the middle- and high-dose areas. Moreover, the low-dose areas showed a significantly lower melanin content index (MCI) compared with the middle- and high-dose areas (F = 4.2,P < 0.05), together with a marked reduction in the extent of pigment deposition, melanin granules, melanocyte number and density. Conclusions The efficacy of Q-switched ruby laser on skin pigmentation in Guinea pigs is correlated with the energy density and treatment frequency, and, low intensity and high frequency are often associated with a better treatment outcome.

Estudo experimental da aplicação retiniana do laser infravermelho via transescleral sob condições de baixa visibilidade / Transscleral infrared laser retinal photocoagulation experimental study under low visibility conditions

OBJETIVOS: Pesquisa experimental, com laser de diodo infravermelho, para estimar a segurança, a reprodutibilidade e a permeabilidade da parede ocular à sua atuação clínica, quando aplicado via transescleral, em condições de baixa visibilidade. MÉTODOS: Submetemos olhos de coelhos pigmentados da raça Nova Zelândia à fotocoagulação retiniana por laser de diodo infravermelho. No olho direito, realizamos fotocoagulação via transescleral sob parâmetros de potência e tempo pré-determinados clinicamente. No olho esquerdo, foram repetidos os mesmos valores da potência e tempo usados no olho direito, desta vez, via transpupilar. Imediatamente e após 2 meses, estudos clínicos baseados na retinografia e histopatológicos foram realizados. RESULTADOS: A permeabilidade da parede ocular, quando da aplicação do laser de diodo infravermelho via transescleral, variou entre 58,95 e 63,87 por cento. A média da permeabilidade da parede ocular a 300 mW (63,14 por cento) mostrou-se significativamente superior àquela da permeabilidade da parede ocular encontrada a 500 mW (59,11 por cento), (P<0,05). CONCLUSÕES: Este estudo sugere a existência da relação dose-resposta em relação aos parâmetros empregados na aplicação do laser de diodo infravermelho via transescleral, com permeabilidade da parede ocular mensurável e reprodutível. Nenhuma rotura, hemorragia ou descolamento da retina ou vítreo foi constatado aos exames subseqüentes às aplicações do laser de diodo infravermelho, o que torna o uso da fotocoagulação via transescleral, no modelo experimental, seguro, mesmo sob condições de baixa visibilidade dos meios.

PURPOSE: Retinal photocoagulation under poor visualization condition is often required. Transscleral infrared laser can be used as an alternative to regular transpupillary treatment. Based upon retinographic measurements, we proposed to estimate the reproducibility as well as ocular wall permeability rate for this treatment. Our primary goal was to evaluate whether this technique can deliver adequate photocoagulation at predetermined parameters without direct retinal visualization. METHODS: In New Zealand pigmented rabbits, optimal transscleral infrared diode laser settings were administered to the right eye. With the same parameters, transpupillary photocoagulation was repeated in the left eye. Retinographic and clinical examinations were performed immediately and two months later. RESULTS: Ocular wall permeability rate varied between 58.95 and 63.87 percent. Average permeability using a power of 300 mW (63.14 percent) was found to be higher than that encountered before its enhancement up to 500 mW (59.11 percent), (P<0.05). CONCLUSIONS: Setting parameters showed dose-response effect. No retinal hole or retinal detachment was noticed in any rabbit. Transscleral infrared photocoagulation appeared to be a reproducible and secure method in the experimental model.

The study of the effect on the image quality in low-dose CT of the paranasal sinuses / 中华放射学杂志

Objective To determine the effect of reducing mA on the diagnostic quality of images and the radiation dose to the lens in patients undergoing paranasal sinus CT. Methods Fifty patients undergoing paranasal sinus CT at 200 mA or 50 mA. The lens dose was measured using thermoluminescent dosemeters [LiF(Mg?Cu?P)]. Image quality was evaluated for six anatomical structures, including middle turbinate, uncinate process, maxillary ostium, ethmoid infundibulum, frontal recess, and cribriform plate. These anatomical structures were assessed as: not seen (0 points), demonstrated but not clearly visualized (1 points), or clearly demonstrated (2 points). Results Mean radiation dose to the lens was significantly reduced from 7.339 mGy (200 mA) to 1.108 mGy (50 mA). No significant difference of image quality between the two mA protocols was found in either rhinosinusitis group or non-rhinosinusitis group. And for rhinosinusitis the image quality showed no significant difference between high-resolution arithmetic and soft arithmetic. Conclusion CT scanning of the sinuses can be performed at greatly reduced mA without loss of diagnostic quality of the images. As far as the rhinosinusitis is concerned, high-resolution arithmetic can not improve the image quality and soft arithmetic is enough.