OBJECTIVE: The present study was aimed at: a) evaluating radiographic procedures and estimating entrance surface air kerma in preterm neonates submitted to chest and abdominal radiography at the unit of neonatology in a public hospital of Belo Horizonte, MG, Brazil; b) estimating the dose to organs and respective risks for cancer as a result from radiation exposure. MATERIALS AND METHODS: Records of patients admitted to the unit of neonatology of this hospital in the period between May and September 2004 were reviewed. Anthropometric data, admission/discharge dates and radiographic studies performed were recorded for each of the patients. The calculation of the entrance surface air kerma was based on the x-ray tube output and irradiation parameters adopted for examinations. Dose to organs was calculated with the aid of the software PCXMC, and the lifetime risk for cancer, with the software IREP. RESULTS: Mean entrance surface air kerma per examination was below the diagnostic reference levels recommended by the European Community. In the most severely irradiated patients, liver, breast and stomach were the organs at highest risk for cancer, with maximum excess relative risk of respectively 3.4%, 2.3%, and 1.7%. CONCLUSION: The present study demonstrated the need for optimization of radiographic procedures in order to reduce the risks for neonates that, in spite of being considered to be low as compared with the benefits, should be reduced to values as low as reasonably achievable.

Keywords: Patient dosimetry, Radiological protection, Pediatric radiology, Cancer risk

OBJECTIVE: The critical analysis of the methodology for evaluating the x-ray beam half-value layer was based on technical standards for radiological protection and quality control in medical and dental diagnoses. MATERIALS AND METHODS: Exposure parameters, experimental set-up, scattering materials, instrumentation, size of radiation field and methodology of data analysis have been taken into consideration for measurements of half-value layer. RESULTS: The half-value layer, in good geometry, measured 2.44 ± 0.02 mmAl. A maximum deviation of 4.1% was found under other geometry conditions. A 98.8% deviation was observed with a different ionization chamber, and scattering material, and 29.5% with another type of detector. CONCLUSION: Results showed that no relevant variation is observed in the half-value layer for different radiation field sizes. On the other hand, the influence of the radiation scattering on the half-value layer overestimation was clearly observed, as well as the half-value layer reduction in the presence of lead used as scattering material. The practical methodology adopted for half-value layer evaluation has shown to be quite reliable, besides evidencing remarkable discrepancies resulting from the adoption of inappropriate methodologies, emphasizing the necessity of establishing a standard procedure for measuring the half-value layer.

Keywords: Half value layer, HVL, Quality control, Diagnostic radiology

OBJECTIVE: The present study was aimed at evaluating the frequency of radiographic assessment of paranasal sinuses in pediatric patients in hospitals of Belo Horizonte, MG, Brazil. Additionally, aspects regarding radiation protection conditions and radiographic parameters were evaluated, and entrance air kerma and organ doses were estimated. MATERIALS AND METHODS: Patients' data and parameters of radiographic technique employed in the assessment of children in the age range between 1 and 16 years were collected in five examination rooms of four hospitals in Belo Horizonte, also taking into consideration the radiation protection aspects. Entrance air kerma calculation was based on the x-ray tubes output, and organ doses were estimated with the PCXMC software. RESULTS: Mean entrance air kerma values found in the five rooms were, respectively, 1398 µGy, 829 µGy, 877 µGy, 1168 µGy and 3886 µGy for patients with ages between 1 and 5 years. CONCLUSION: Most frequently, mento-naso and fronto-naso views are requested in conjunction in the majority of hospitals, which increases the radiation dose to the patients. It may be concluded that the risks for patients can be reduced by means of the utilization of an appropriate x-ray field, non-utilization of antiscattering grids, selection of high voltages and lower exposure times.

Keywords: Pediatric radiology, Patient dose, Organ dose

OBJECTIVE: To evaluate the feasibility of using radiochromic films as an alternative dosimeter to estimate the multiple scan average dose on the basis on kerma profiles. MATERIALS AND METHODS: The radiochromic films were distributed in cylinders positioned in the center and in four peripheral bores of a standard abdominal phantom utilized for computed tomography dosimetry. RESULTS: Values for multiple scan average dose values corresponded to 13.6 ± 0.7, 13.5 ± 0.7 and 18.7 ± 1.0 mGy for pitch of 0.75, 1.00 and 1.50, respectively. CONCLUSION: In spite of results showing lower values than the reference level for radiodiagnosis (25 mGy) established by the Brazilian regulations for abdominal studies, it is suggested that there is room to optimize procedures and review the reference level for radiodiagnosis in Brazil.

Keywords: Kerma profiles; Computed tomography; Radiochromic films; MSAD.

OBJECTIVE: To suggest a national value for the diagnostic reference level (DRL) in terms of activity in MBq.kg^-1, for nuclear medicine procedures with fluorodeoxyglucose (¹⁸F-FDG) in whole body positron emission tomography (PET) scans of adult patients. MATERIALS AND METHODS: A survey on values of ¹⁸F-FDG activity administered in Brazilian clinics was undertaken by means of a questionnaire including questions about number and manufacturer of the installed equipment, model and detector type. The suggested DRL value was based on the calculation of the third quartile of the activity values distribution reported by the clinics. RESULTS: Among the surveyed Brazilian clinics, 58% responded completely or partially the questionnaire; and the results demonstrated variation of up to 100% in the reported radiopharmaceutical activity. The suggested DRL for ¹⁸F-FDG/PET activity was 5.54 MBq.kg^-1 (0.149 mCi.kg^-1). CONCLUSION: The present study has demonstrated the lack of standardization in administered radiopharmaceutical activities for PET procedures in Brazil, corroborating the necessity of an official DRL value to be adopted in the country. The suggested DLR value demonstrates that there is room for optimization of the procedures and ¹⁸F-FDG/PET activities administered in Brazilian clinics to reduce the doses delivered to patients. It is important to highlight that this value should be continually revised and optimized at least every five years.

Keywords: Nuclear medicine; Positron emission tomography; Diagnostic reference level; Radiopharmaceutical ¹⁸FFDG.

OBJECTIVE: Aiming at contributing to the knowledge on doses in computed tomography (CT), this study has the objective of determining dosimetric quantities associated with pediatric abdominal CT scans, comparing the data with diagnostic reference levels (DRL). MATERIALS AND METHODS: The study was developed with a Toshiba Asteion single-slice CT scanner and a GE BrightSpeed multi-slice CT unit in two hospitals. Measurements were performed with a pencil-type ionization chamber and a 16 cm-diameter polymethylmethacrylate trunk phantom. RESULTS: No significant difference was observed in the values for weighted air kerma index (C_W), but the differences were relevant in values for volumetric air kerma index (C_VOL), air kerma-length product (P_KL,CT) and effective dose. CONCLUSION: Only the C_W values were lower than the DRL, suggesting that dose optimization might not be necessary. However, P_KL,CT and effective dose values stressed that there still is room for reducing pediatric radiation doses. The present study emphasizes the importance of determining all dosimetric quantities associated with CT scans.

Keywords: Pediatric computed tomography scans; Dosimetric quantities; Weighted dose index; Volumetric air kerma index; Air kermalength product.

OBJECTIVE: The present study was aimed at evaluating the effective radiation dose in patients submitted to PET/CT for the diagnosis of mild cognitive impairment. MATERIALS AND METHODS: TLD-100 detectors inserted into an Alderson Rando® anthropomorphic phantom were utilized to measure the absorbed dose coming from the CT imaging modality. The anthropomorphic phantoms (male and female adult versions) were submitted to the same technical protocols for patients' images acquisition. The absorbed dose resulting from the radiopharmaceutical injection was estimated by means of the model proposed by the ICRP publication 106. RESULTS: The effective dose in patients submitted to this diagnostic technique was approximately (5.34 ± 1.99) mSv. CONCLUSION: Optimized protocols for calculation of radioactive activity injected into patients submitted to this diagnostic technique might contribute to reduce the effective radiation dose resulting from PET/CT in the diagnosis of mild cognitive impairment.

Keywords: Dosimetry; PET/CT; Mild cognitive impairment.

OBJECTIVE: To evaluate the level of ambient radiation in a PET/CT center. MATERIALS AND METHODS: Previously selected and calibrated TLD-100H thermoluminescent dosimeters were utilized to measure room radiation levels. During 32 days, the detectors were placed in several strategically selected points inside the PET/CT center and in adjacent buildings. After the exposure period the dosimeters were collected and processed to determine the radiation level. RESULTS: In none of the points selected for measurements the values exceeded the radiation dose threshold for controlled area (5 mSv/year) or free area (0.5 mSv/year) as recommended by the Brazilian regulations. CONCLUSION: In the present study the authors demonstrated that the whole shielding system is appropriate and, consequently, the workers are exposed to doses below the threshold established by Brazilian standards, provided the radiation protection standards are followed.

Keywords: Dosimetry; Thermoluminescence dosimetry; PET/CT.