ENTRANCE SKIN DOSE MEASUREMENTS FOR PAEDIATRIC CHEST X-RAYS EXAMINATIONS IN BRAZIL

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1 ENTRANCE SKIN DOSE MEASUREMENTS FOR PAEDIATRIC CHEST X-RAYS EXAMINATIONS IN BRAZIL Mohamadain, K.E.M. 1 ; Azevedo, A.C. P. 2 ; da Rosa L.A.R. 3 ; Goncalves O.D. 4 ; Guebel, M.R.N. 5 and Mota, H. C. 3 1 Sudan University of Science and Technology, Faculty of Sciences, Physics Department, Sudan. (On leave for Ph.D. sandwich program in Brazil) 2 Departamento de Radiología, Faculdade de Medicina, UFRJ e SES do Rio de Janeiro, Brazil. 3 Departamento de Física Médica, Instituto de Radioprotecáo e Dosimetría, Av. Salvador Allende s/n, , Rio de Janeiro, RJ, Brazil. 4 Departamento de Física Nuclear, Instituto de Física, UFRJ, Rio de Janeiro, Brazil. 5 Instituto de Pediatría e Puericultura Martagáo Gesteira, UFRJ Radiation protection in paediatric radiology deserves special attention since it is assumed that children are more sensitive to radiation than adults. The aim of this work was to estimate the Entrance Skin Dose (ESD) and the scattered dose in different organs (thyroid, gonad, ovary) for the frontal and lateral chest X-ray exposure to paediatric patients and to compare this result with the criteria of the European Commission for radiation dose to patients. Three examination techniques were used, PA, AP and lateral positions. This study was carried out in the paediatric unit of the University Hospital of the Federal University of Rio de Janeiro. For patient measurements two different TL dosimeters were used, namely LIF:Mg,Ti and CaSO^Dy. The age intervals considered were 0-1 year, 1-5 years, 5-10 years and years. The results obtained with both dosimeters are similar and the ESD values evaluated for the different age intervals considered are comparable with the values found in Sweden, Germany, Spain and Italy. For dose measurements due to scattered radiation, important values are found only in case of new-borns, probably due to the field size considered. Introduction Quality Assurance Programmes and Quality Control initiatives in general diagnostic radiology have been developed in several countries in the past 16 years, mainly in 4) Europe'. However, the need for special QAP for paediatric patients were first realised early in the 1980s (56). The main goals were to improve the diagnostic information and to reduce the patient dose to a minimum; the ALARA principle^'. The efforts towards QA in paediatric radiology were at first dominated by the principle of justification and also by the concepts of "efficacy/efficiency" (8 9). The WHO Report 757 compiled such principles for a number of common diseases in paediatrics and emphasised the term "rational use of diagnostic imaging" <10). The second important principle of "optimisation"' 11) is contemplated by the document "Quality Criteria for Diagnostic Radiographic Images in Paediatrics"' 12 ' and an earlier developed document for adults, "Quality Criteria for Diagnostic Radiographic Images" <13>. In 1998 the Brazilian Sanitary Surveillance and the Ministry of Health of Brazil published the decree 453 (14> establishing radiation protection guidelines for diagnostic radiology in medicine and odontology. Among the legal exigencies contained in the decree, it is mandatory the implantation of QAP at all institutions that use ionising radiations. In the field of odontology, the Instituto de Radioprotecáo e Dosimetría (IRD), Brazil, has been developing a very important programme since 1980 (15) with good results. Quality assurance in paediatric radiology is still more important, since it is i

2 known that children are more sensitive to radiation than adults. Therefore, in this case, closer attention should be paid to improve the diagnostic information, reducing the child dose as much as possible' 5,6 *. As a preliminary evaluation, the aim of this work was to estimate the Entrance Skin Dose (ESD) and the scattered dose in different organs (thyroid, gonad, ovary) for the frontal and lateral chest X-ray exposure to paediatric patients and to compare this result with the criteria of the European Commission for radiation dose to patients. Three examination techniques were used, PA, AP and lateral positions. This study was carried out in the paediatric unit of the University Hospital of the Federal University of Rio de Janeiro. For patient measurements, two different TL dosimeters were used, namely LiF:Mg,Ti and CaSO^Dy. The age intervals considered were 0-1 year, 1-5 years, 5-10 years and years. Materials and Methods The thermoluminescent (TL) dosimeters used were LiF:Mg,Ti and CaSO^Dy. The LiF:Mg,Ti was produced by Bicron, USA, as square chips, the so-called TLD-100, and the CaS0 4 :Dy was manufactured by the Instituto de Pesquisas Energéticas e Nucleares (IPEN), Brazil, as circular chips. Both dosimeters were evaluated in a TL reader Harshaw The individual relative sensitive factors and repeatability for all dosimeters used in this work were investigated for gamma radiation, 1 cgy, 1 Cs. TL dosimeter calibration factors were determined for different X-rays beams Kvp obtained with a Siemens Polymat 50 equipment. Dose evaluations for TL dosimeter calibration were carried out with a dosimetric system Radical, model 9015, with a 6 cc chamber 90 X. The X-rays kilovoltages used were 63, 66, 70, 73, 77, 81, 85, 90 and 96 kv. Control dosimeters having good repeatability, better than 1%, were always employed in order to detect possible TL system changes. The TL dosimeter intrinsic background was always taken in consideration for dose evaluation, since the dose levels investigated were usually low. Using TL dosimeters, the dose, D, during paediatric radiology was determined by formula (1) showed below. D = (L-L B g).fs.fcfcom (1) L is the TL reading in nc, Leg is the intrinsic background of the TL dosimeters in nc, f s is the sensitive factor, f c is the calibration factor and fcom is the factor generated by the control dosimeters. In the hospital, during examinations, the age, sex, weight and technical parameters of exposure (tube voltage, current, time product, SSD) were noted. Three individual TL dosimeters of each type were placed on the skin of each patient in different places. At the centre of the primary beam, two TL dosimeters were placed, one TLD-100 and a CaS0 4 :Dy. For scattered radiation, CaS0 4 :Dy dosimeters were placed close to gonads, thyroid and ovary. For examinations, the equipment used was a RORIX Type DR124/30/50. The energies used, according to the type of examination and the patient age, varied from 55 up to 77 kv for AP projection, from 57 up to 96 kv for PA projection and from 66 up to 109 kv for lateral projection. Results The TLD average, individual reproducibility was about 1%, for both materials, for a dose 1cGy due to 137 Cs irradiations. Of course, if very low doses are intended to be 2

3 measured, the repeatability will be worse due to the higher influence of the TL dosimeter intrinsic background. Results for AP, PA and Lateral examinations are presented in Tables I, II and III for different age intervals. Table I: Doses measured for AP examinations. TL dosimeters at the centre of the beam.(a) CaS0 4 :Dy TLD-100. (A) 0-1 0,06± 0,002 0,09±0,002 0,07±0, ±0,0007 0,18±0,008 0,07±0, ,039± 0,003 0,08±0,003 0,05±0, ±0,001 0,17+0,002 0,06+0,001 Table II. Doses measured for PA examinations. TL dosimeters at the centre of the beam.(a) CaS0 4 :Dy TLD-100. (A) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

4 Table III. Doses measured for Lateral examinations. TL dosimeters at the centre of the beam. (A) CaS0 4 :Dy TLD-100 (A) ± ±0, ± ± ± ± ± ± ± ± ± ± ±0, ± ± ± ± ± ± ± ± Figure 1 presents a comparison between the present results and the values obtained in different European countries. All values are compared with the reference level adopted in Europe. Doses values measured in Rio de Janeiro are at same levels of European results, excepting the values measured in Holland, that are very low and completely different from the other results. They do not represent the European situation. ESD for pediatric chest Xray (0-5) year For scattered radiation no significant dose values were measured, excepting in case of new-borns. Probably, in these cases, not only scattered radiation is measured, but also the direct beam, since new-borns bodies are very small and are almost completely irradiated during examination. Conclusions 4

5 The results obtained with both dosimeters are similar and the dose values evaluated for the different age intervals considered are comparable with the values found in Sweden, Germany, Spain and Italy. The maximum doses evaluated in Brazil are higher than the European reference levels. However, these reference levels are not achieved by Sweden, Germany, Italy and Spain as well. For dose measurements due to scattered radiation,significant values are found only in case of new-borns, probably due to the field size considered. REFERENCES 1. BÁK. Leitlinien der Bundesárztekammer zur Qualitátssicherung in der Róntgendiagnostik. Deutsches Arzteblatt 86, (1989). 2. DIN 6868/1. Sicherung der Bildqualitát in Róntgendiagnostischen Betrieben; Allgemeines (Beuth Verlag GmbH, Berlin) (1985). 3. Stender, H-S and Stieve, F-E. Praxis der Qualitátskontrolle in der Róntgendiagnostik (Gustav Fischer Verlag, Stuttgart - New York) (1986). 4. Da Silva, E. T. Avaliacáo de Doses em Radiodiagnóstico Pediátrico M. Sc. Thesis COPPE / UFRJ / Brazil. In Portuguese. (1999) 5. Fendel, H., Schneider, K., Schófer, H., Bakowski, C. and Kohn, M. M. Optimisation in Pediatric Radiology: Are There Specific Problems for Quality Assurance in Pediatric Radiology? In: Technical and Physical Parameters for Quality Assurance in Medical Diagnostic Radiology: Tolerances, Limiting Values and Appropriate Measuring Methods. Eds B. M. Moores et al. BIR 18 (London: British Institute of Radiology). Pp (1985). 6. Fendel, H. Symposium: The Status of Paediatric Radiology in Europe. The Principles for Rational Use and Optimisation of Diagnostic Imaging in Paediatrics. 27 th Congress of ESPR, Munich (1990). 7. ICRP. Recommendations of the International Commission on Radiological Protection. Publication 26 (Oxford: Pergamon Press) (1977). 8. Fendel, H., Schneider, K., Bakowski, C. and Kohn, M. M. Die Auswirkung Diagnostischer Strahlenanwendungen in der Kinderheilkunde. 1. Bericht (Bonn: Bundesministerium des Innern) (1985). 9. Fendel, H., Schneider, K., Bakowski, C. Glas, J., Drews, K. and Kohn, M. M. The Efficacy of Diagnostic Radiation in Paediatrics. 2 n d Report (Bonn: Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit) (1986). 10. World Health Organisation - Study Group. Radional Use of Diagnostic Imaging in Paediatrics. WHO Technical Report Series 757 (Geneva: WHO) (1987). 11. Fendel, H., Schneider, K., Bakowski, C. and Kohn, M. M. Specific Principles for Optimisation of Image Quality and Patient Exposure in Paediatric Diagnostic Imaging. Optimisation of Image Quality and Patient Exposure in Diagnostic Radiology. Eds B. M. Moores et al. BIR 20 (London: British Institute of Radiology) pp (1989). 12.CEC. Quality Criteria for Diagnostic Radiographic Images in Paediatrics. Working Document No. XII/307/91 (June 1992). 13. CEC. Quality Criteria for Diagnostic Radiographic Images. Working Document No. XII/173/90, 2 n d edn (June 1990). 14. Diretrizes de Protecao Radiológica em Radiodiagnóstico Médico Odontológico, Portaria 453 do Ministerio da Saúde, D O U 103, 01/06/98. (1998). 15. Da Rosa, L. A. R., Maréchal, M. H. H., Carlos, M. T. e Feital, J. C. Calibration of TL Detectors for Skin Entrance Dose Postal Quality Control in Dental Radiology V Regional Congress on Radiation Protection and Safety, held in Recife, Pernambuco, Brasil, 29 / / 05 / Proceedings in compact disc. (2001). 5