2007 International Nuclear Atlantic Conference - INAC 2007 Santos, SP, Brazil, September 30 to October 5, 2007 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-02-1 DOSE EVALUATION IN UROGRAPHY RADIOLOGICAL PROCEDURES Alessander S. do Carmo 1, Delson Braz 1 and Regina C. Barroso 2 1 Laboratório de Instrumentação Nuclear (LIN / PEN / COPPE / UFRJ) Centro de Tecnologia Bloco G Sala 206. Cidade Universitária, Ilha do Fundão. 21949-900 Rio de Janeiro, RJ Brasil. acarmo@con.ufrj.br delson@lin.ufrj.br 2 Instituto de Física (IF / UERJ) Rua São Francisco Xavier 524 Bloco B Sala 3020. 20550-900 Rio de Janeiro, RJ Brasil. cely@uerj.br ABSTRACT The aim of this study was to carry out the measurements of kerma-area product (KAP) with 47 patients during the urography examinations in two hospitals located in the city of Rio de Janeiro - Alpha and Bravo Hospitals - employing a KAP measurer. 16 out of 47 patients were within the biometric variations defined by the Decree Nº 453 of the Ministry of Health of Brazil on June 1 st, 1998, as being considered typical adult patients. The average values of KAP obtained through the measurer for intravenuous urography examinations for all radiographic projections and for AP projections were 3,937.71 cgy cm 2 and 3,596.56 cgy cm 2 in Alpha Hospital. In Bravo Hospital, the average values of KAP for the same examination for all radiographic projections and for AP projections were 641.81 cgy cm 2 and 586.44 cgy cm 2, and for uretrocistography examinations the average values of KAP were 576.32 cgy cm 2 for all radiographic projections and 288.16 cgy cm 2 for AP projections. This study shows the adequacy of the methodology to carry out the examinations once the KAP measurer is a very simple and important tool for dose measurements in patients to be established and/or compared with reference levels and quality control. 1. INTRODUCTION In the 1960s there were many proposals for dosimetric measurement in patients. However, the dose measurers in patients were more complex for they had to consider the types of tissues exposed to radiation, as well as the dose variation over the irradiated anatomic structure. On the other hand, when the dose is measured in one point, there is no notion of the irradiated or the volume area. In order to solve these problems several integrated instruments with distinct quantity indications were developed and among them, the kermaarea product (KAP). The kerma-area product is the most adequated quantity to measure the degree of the patient s exposition in radiodiagnostic and to express the reference levels. The KAP is a quantity that is connected with the risk of inducing from the radioinduced effects for it considers, besides the air kerma, the irradiated area which indicates the quantity of energy given to the patient [1].
Through the kerma-area product it is possible to evaluate the dose rate produced multiplied by the time and the field size of radiation as from the application of tension and current on the X-ray tube with a given filtration, Fig. 1. The focal distance is not considered because the dose reduces with the Inverse Squared Law and the radiation field size increases with the squared of the distance so that the product is kept constant. It is important to emphasize that the kerma-area product measurers are projected in such way that their response do not depend on the energy for the X-ray beams on the quality zone of radiodiagnostic. Figure 1. Principle of the measures of KAP and the events that influence the patient s exposition, being the relation among the distance, the area and the kerma [1]. In 1969, the ICRP included on its recommendations the employment of KAP measurers considering its importance to professional training of radiodiagnostic and thus restricting the field size of the radiation or the exposure time [1]. 2. MATERIALS AND METHODS Two devices of X-rays were used to accomplish the urography examinations in two hospitals located in Rio de Janeiro: CGR - model triplunix 5 (Alpha Hospital), and GE - model Proteus XR/a (Bravo Hospital). The dose measurements in the abdominal region (intravenous urography examinations) and in the symphysis pubis region (uretrocistography examinations) were carried out employing a kerma-area product measurer (PTW Freiburg, model DIAMENTOR M2, Fig. 2 on the left), connected to an ionization chamber (PTW Freiburg, model 57523, Fig. 2 on the right), with a size of 17 cm x 18.5 cm x 1.7 cm and a 70 % of transparency to the visible light fixed under the collimation system on the X-rays tube, Fig. 3. Its connection was made through a connector cable (PTW Freiburg, type K3S). The measurer
had to be recalibrated due to its installation in each one of the X-rays equipments used in this study [2] [3], through the employment of a dose measurer connected to an ionization chamber of reference duly calibrated (PTW Freiburg, model CONNY II). Decree Nº 453 published by the Ministry of Health of Brazil on June 1 st, 1998 defines the typical adult patient as an individual that presents biometric variations between 60 kg and 75 kg of corporal mass and 1.60 m and 1.75 m of height [4]. Moreover, the representative dose value given to the patients can be determined, among other methods, by the 3 rd quartile of distribution of dose in patients for each type of radiological exams. In Alpha Hospital, 9 out of 24 patients evaluated for intravenous urography examinations presented characteristics of typical adults. In Bravo Hospital, 5 out of 17 patients evaluated for intravenous urography examinations and 2 out of 6 patients evaluated for uretrocistography examinations also presented these characteristics. The measurements of KAP for all the projections (AP, PA and oblique) and AP projections were considered. Figure 2. On the left, the kerma-area product measurer PTW Freiburg DIAMENTOR M2; on the right, the ionization chamber PTW Freiburg 57523 [5]. Figure 3. On the left, the ionization chamber fixed on the X-rays tube collimation system; on the right, the assembly layout for the measurements of KAP in patients during the urography examinations.
3. RESULTS All the 47 patients submitted to the urography examinations were evaluated with kerma-area product PTW DIAMENTOR M2 in the two hospitals. The total number of radiographic expositions carried out during the intravenous urography examinations in Alpha Hospital was 201. In Bravo Hospital, the total number of radiographic expositions in intravenous urography examinations was 159 and for the uretrocistography examinations the total number of radiographic expositions was 50. Figures 4, 5 and 6 show the graphics concerning to the patients expositions related to each one of the KAP values evaluated in the two hospitals. 2500 KAP (cgy cm2) 2000 1500 1000 500 0 F1 F2F3 F4 M2F5 F6 M3M4 M5 F7M6 M7 F13 M11 M12F14 M13 M14 M15 M16F15F16 M17 Figure 4. Graphic patients x KAP expositions for intravenous urography examinations in Alpha Hospital. KAP (cgy cm2) 350 300 250 200 150 100 50 0 FM1 FM3 FM5 FF3 FM6 FM7 FF4 FM8 FM9 FM10 FF7 FF8 FF9 FF6 FF10 FM14 FF13 Figure 5. Graphic patients x KAP expositions for intravenous urography examinations in Bravo Hospital.
250 KAP (cgy cm2) 200 150 100 50 0 FM2 FF1 FM11 FM12 FM13 FF11 Figure 6. Graphic patients x KAP expositions for uretrocistography examinations in Bravo Hospital. Analyzing the graphics it could be noticed a great variation in the values of kerma-area product for the same patient because the technical parameters, which were used during the measurements (kv, mas), were not kept constant. The same behavior was observed when the other patients were analyzed in the same hospital. Table 1 shows the results of average values and the 3 rd quartile of KAP for the patients submitted to urography examinations in both hospitals, taking into consideration all the radiographic projections and AP projections. Table 1. Average values and 3 rd quartile of KAP for urography examinations Hospital (Examinations) Alpha (Intravenous urography) Bravo (Intravenous urography) Bravo (Uretrocistography) Adults in general (n = 24) Typical adults (n = 9) Adults in general (n = 17) Typical adults (n = 5) Adults in general (n = 6) Typical adults (n = 2) KAP values (cgy cm 2 ) All projections 3 rd Average quartile AP projection 3 rd Average quartile 3,571.56 4,280.87 3,210.92 3,634.52 3,937.71 4,812.61 3,596.56 3,637.83 1,015.08 1,563.93 932.64 1,418.85 641.81 787.95 586.44 787.95 684.80 1,038.18 544.16 909.07 576.32 705.43 288.16 303.14
The average values of KAP obtained from the measurer for intravenouous urography examinations in typical adult patients for all the projections and for AP projections were 3,937.71 cgy cm 2 (3 rd quartile 4,821.61 cgy cm 2 ) and 3,596.56 cgy cm 2 (3 rd quartile 3,637.83 cgy cm 2 ) respectively, in Alpha Hospital with a difference of 8.66 %. For Bravo Hospital, the average values of KAP for the same examination in typical adult patients for all the projections and for AP projections were 641.81 cgy cm 2 (3 rd quartile 787.95 cgy cm 2 ) and 586.44 cgy cm 2 (3 rd quartile 787.95 cgy cm 2 ) respectively, with a difference of 8.63 %. The average value of KAP in intravenouous urography examinations in Alpha Hospital was 71.6 % greater than in Bravo Hospital, due to the fixed value of current-time product (60 mas) in all patients evaluated. This result was influenced by the X-ray equipment which was old and by the lack of training of the radiology professionals. For uretrocistography examinations in Bravo Hospital, the average values of KAP in typical adult patients were 576.32 cgy cm 2 (3 rd quartile 705.43 cgy cm 2 ) for all the projections and 288.16 cgy cm 2 (3 rd quartile 303.14 cgy cm 2 ) for AP projections, with a difference of 50 %. However, this exam was not carried out in Alpha Hospital over the dosimetric measurements with KAP measurer for its frequency was lower than the intravenous urography examinations. 4. CONCLUSIONS The number of typical adult patients evaluated on this study for the urography examinations in the two hospitals was very low in comparison with the rest of the patients who were out of the biometric variations. This study may help for future works with a greater number of typical adult patients to be evaluated in intravenous urography and uretrocistography examinations using KAP measurers, and also to improve the statistics in obtaining more significant results of measurements so that the reference levels can be evaluated. The method used in this study is appropriated to carry out the examinations once the KAP measurer is a very simple and an important tool for dose measurements in patients with the purpose of establishing or comparing the reference levels and quality control. REFERENCES 1. L.V. CANEVARO, Otimização da Proteção Radiológica em Fluoroscopia: Níveis de Referência de Diagnóstico, Doctorate Tesis, Rio de Janeiro State University UERJ, Rio de Janeiro, Brazil (2000). 2. IPSM, NRPB & CoR. National Protocol for Patient Dose Measurements in Diagnostic Radiology, Health Protection Agency, Chiltoon, UK (1992). 3. ICRU. Patient Dosimetry for X-Rays Used in Medical Imaging. Report Nº 74, Vol. 5 (December, 2005). 4. Decree Nº 453. Diretrizes de Proteção Radiológica em Radiodiagnóstico Médico e Odontológico, Ministry of Health, Brazil (1998). 5. PTW Freiburg DIAMENTOR M2 & ionization chamber, http://www.ptw.de (2006).