Digital chest radiography: collimation and dose reduction

Transcription

1 Digital chest radiography: collimation and dose reduction Poster No.: C-1939 Congress: ECR 2015 Type: Scientific Exhibit Authors: J. Debess, K. Johnsen, K. Vejle Sørensen, H. Thomsen ; Aalborg Øst/DK, Viborg/DK Keywords: Radioprotection / Radiation dose, Thorax, Digital radiography, Dosimetry DOI: /ecr2015/C-1939 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 13

2 Aims and objectives Overall purpose: Quality improvement of basic radiography focusing on collimation and dose reduction in digital chest radiography. First aim: To evaluate the collimation of digital chest radiography; second aim to analyze the impact of collimation on dose to thyroid, breast and stomach. Methods and materials A retrospective study of digital chest radiography to evaluate the primary x-ray tube collimation of the PA and LAT radiographs was performed. Collimation data from one hundred eighty-six self-reliant female patients between 15 and 55 years of age were included in the study. In addition the dose area product (DAP) was recorded from the radiographs. The clinical research was performed between September and rd November 2014 where 3 year radiography students collected data in four Danish x-ray departments using identical procedures under guidance of clinical supervisors (Fig 1.) None of the data was personally identifiable. Correct collimation, two centimeters on all sides, was determined according to European (1) and regional Danish guidelines. The area between current and optimal collimation was calculated. The experimental research was performed in December 2014 on a Siemens Axiom Aristos digital radiography DR system. Chest exposures were 150 kv, 1,25-3,3 mas and SID of 180 centimeters using an anthropomorphic phantom (Alderson Radiation Therapy Phantom) and Thermo luminescent Dosimeter (TLD). The TLDs were prepared by and readings conducted at the University College of Northern Denmark, Department of Radiography, Aalborg Denmark using Rados RE-2000 and IR-2000 TLD reader with batch homogeneity < 5%. Eight control TLD tablets were used to record the background radiation, which was subtracted from the measurements. Absorbed point dose to risk organs right breast, thyroid and stomach were measured at different collimations with steps of two to four centimeters. For the PA position two TLD tablets were placed in the right breast: one in a lateral (I), (Fig. 2) and one in a medial centered position (II). Third TLD was placed in right thyroid (III) and the fourth in the place of curvature minor of the stomach (IV), (Fig. 3). The Alderson phantom was placed PA and central fan beam was centered on the middle of the seventh thoracic spine. The light beam measure was used to ensure the different collimations (Fig 4). Six exposures were conducted for each collimation with new TLD for Page 2 of 13

3 every exposure. The radiographs were evaluated with respect to DAP, positioning and exposure parameters at the workstation fig. 5. For the statistical analyses the SPSS software package was used (PASW Statistics 22 (version , SPSS Inc., Chicago, IL). Descriptive statistics included t-test for group differences with respect for different collimations. Images for this section: Page 3 of 13

4 Fig. 1: Guideline for measuring of collimation Page 4 of 13

5 Fig. 2: TLD placed in the right breast Page 5 of 13

6 Fig. 3: TLD placed in position: stomach Page 6 of 13

7 Page 7 of 13

8 Fig. 4: PA chest x-ray of Alderson Fig. 5: Image: PA chest Alderson excessive collimation Page 8 of 13

9 Results Clinical study Data included 186 PA chest radiographs of self-reliant women, mean age 2 40 years and mean DAP value 2,3 dgyxcm (min 1.0 -max 7.3). Only half of the PA radiographs were correct positioned (Fig. 6). The retrospective measurements of the original not post processed chest radiographs showed that 76 % to 90 % had excessive not collimated areas depending on side. Especially the not collimated area from sinus phrenico-costalis to border was large (Fig 7). Table 1. Radiation dose measured at different collimation Radiation absorbed point dose micro Gy: Mean (95%CL) Body parts Correct collimation + 2 cm collimation + 5 cm collimation + 8 cm collimation cm collimation Breast I NA NA ( ) ( ) ( ) NA NA ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) Breast II Thyroid III Stomach IV 11,2 ( ) Phantom study Table 1. shows the results from the experimental study showing a significant increase of 25% (p<0.01) in point absorbed dose to the stomach at 10.2 cm excessive collimation. No increased dose was found for the other organs, which may be the result of the position of the TLD tablets that already where very close to the collimation border at correct collimation. We found that DAP values increased with 54% (p>0.01) from correct to 10.2 cm excessive collimation. Page 9 of 13

10 Images for this section: Fig. 6: Percentiles og correct an incorrect positioned chest radiograph Page 10 of 13

11 Fig. 7: Collimation PA chest sinus phrenicus costalis Page 11 of 13

12 Conclusion Quality of basic radiography with respect to collimation and dose reduction in digital chest radiographs can be improved. From 76 % to 90 % of the evaluated radiographs had excessive collimation. Collimation should be reduced as chest x-ray is one of the most common examinations with 641,561 examinations performed on Danish departments of medical imaging in 2013 (2). Pervious studies evaluating lumbar spine radiographs found likewise larger collimation than acceptable (3,4). The radiation dose of 0.1 msv for the individual patient is relatively low, but due to the large number of examinations, the collective radiation dose can be significant (5,6). Therefore, a reduction of the dose for each patient focusing on the ALARA (as low as reasonably achievable) principle is important (6). It is especially essential to improve the collimation from sinus phrenicostalis to border as the TLD experiment showed a significantly increase in dose of 25 % to the stomach with lack of proper collimation. Correct positioning and collimation of digital chest radiographs can reduce the radiation dose to the patients significant and on that basis improve the quality of basic radiography. Personal information References 1. Blanc D. European guidelines on quality criteria for diagnostic radiographic images. Radioprotection 1998;32(1): Statens Serum Institut. Radiologiske ydelser Debess,J., Thomsen H, Conradsen J, Odgaard T. Billedkvalitet og billedevalueringskriterier for thorax og columna lumbalis. Kvalitetsog professionsudvikling i radiografien - med fokus på evaluering af "præbillede" og færdigt PACS billede, samt læring og faglig udvikling. Page 12 of 13

13 2011;1(1): Zetterberg, LG, Espeland. Lumbar spine radiography - poor collimation practices after implementation of digital technology. The British Journal of Radiology 2011; jun (84): Sundhedsstyrelsen. Strålingsguiden - ioniserende stråling. 2012;2.0:26. Bushberg JT, Seibert JA, Leidholt E,. Boone JM. The essential physics of medical imaging. 2nd ed. Philadelphia: Wolters Kluwer Health /Lippincott Williams & Wilkins, Page 13 of 13