Strategies for the reduction of exposure of medical staff in the CT operating room

Transcription

1 Strategies for the reduction of exposure of medical staff in the CT operating room Poster No.: C-3025 Congress: ECR 2010 Type: Educational Exhibit Topic: Radiographers Authors: M. Körner, U. Linsenmaier, M. F. Reiser, S. Wirth; Munich/DE Keywords: CT-guided interventions, Radiation protection, Dosimetry DOI: /ecr2010/C-3025 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 31

2 Learning objectives Exposure doses in the CT scanning room dramatically vary according to characteristic isodose curves. Knowledge of "safe" points where radiation dose is minimal. Distance to the isocenter should be optimized according to the inversesquare law. Limit the presence of medical staff in the scanning room. Regular education of staff results in significant reduction of exposure. Background During CT-guided interventions or in examinations of patients that are critically ill, ventilated, or instable, physical presence of medical staff such as technicians, radiologists, or anesthetists in the examination room is inevitable. When radiation is applied, the persons in the room are exposed to scattered radiation even when wearing protective gear. The absorbed dose is very variable and depends mainly on the dose applied to the patient, the distance from the source of radiation, and the protective gear worn [1-5]. Although the average staff doses are reported to be quite low in a range of several µsv per examination, these doses will accumulate considerably in persons that frequently are present during such examinations and interventions. Radiation for the staff being present in the room during CT examinations can be reduced significantly by using personal protecting gear or by simply keeping distance from the gantry [6-8]. However, a representative study with non-radiologist physicians showed that about two thirds underestimated the radiation dose produced by a CT examination [9]. With that knowledge it seems quite obvious that the dose from scattered radiation will also be underestimated by staff from other departments being present in the scanner room, resulting in insufficient protection or keeping inefficient distance from the radiation source. Usually, persons that have to be present during CT-guided interventions have to wear protective gear. Even if this rule is mostly strictly followed, it is quite common that aprons are not handled with enough care (Fig. 1 on page 3), resulting in partial (Fig. 2 on page 3) or complete material failure (Fig. 3 on page 4). Even when protection is used, one has to be aware that X-rays are only attenuated by absorbing material (Figs. 4 on page 5 and 5 on page 6). Absorption is dependent of the materials and the thickness of the shield (Fig. 6 on page 7). Page 2 of 31

3 Distance to the source of radiation is another method to reduce exposure of the staff. Knowledge of the distance-square law helps to further reduce personal exposure (Fig. 7 on page 8). CT devices produce charcterist patterns of dose distribution, so called isodose curves (Fig. 8 on page 9). Staff should be introduced to this fact to know where points of low radiation are located in the room to cover there when radiation is applied. In the following section we provide data from our institution how to keep staff alert and informed about most of these facts. Images for this section: Fig. 1: These image show aprons being "stored" after interventions. Page 3 of 31

4 Fig. 2: Example of partial material failure. Page 4 of 31

5 Fig. 3: In this glove one hole was large enough to fit a complete thumb. Page 5 of 31

6 Fig. 4 Page 6 of 31

7 Fig. 5: Image obtained of a ruler with lead marks. The detector was covered with a lead apron. The marks are clearly visible even the shield was applied. Page 7 of 31

8 Fig. 6 Page 8 of 31

9 Fig. 7 Page 9 of 31

10 Fig. 8: Typical isodose curves for the CT installed at our institution. Page 10 of 31

11 Imaging findings OR Procedure details 1. Dose measurements The first step was to determine the places in the CT operating room that are frequently occupied by staff (Figs. 1 on page 12 and 2 on page 13). The locations were marked on the floor (Fig. 3 on page 14). For simulation of scattered radiation produced by a patient, an anthropomorphic phantom was placed on the CT table (Fig. 3 on page 14). The dose was measured with ionization chambers that were placed on the floor marks at a height of 120 cm from the floor (Fig. 4 on page 15). We used a standard abdomen scan protocol (scan range: 492 mm. CTDIvol: mgy, mean DLP: mgy*cm (SD: ± 0.13). The results from the dose measurements are displayed in Figure 5 on page 16. Even if using an apron reduces the dose by over 90%, it is quite remarkable that the best protection in the CT room is not distance and personal protective gear but moving into the "shadow" of the gantry (points 1 and 2), where we measured the lowest dose even when no apron is worn. This is an important fact to be taught to the staff and should be always remembered when being present in the CT room during examinations. As expected, the dose was highest next to the gantry bore. This implicates that only the persons directly involved should stand here, and only for a limited time. This is also important when residents or students are present during interventions. When radiation is applied (e.g. fluoroscopy), the operator should tell the anesthetist to seek cover. In most cases, manipulation of the patient can be stopped for this period. 2. Questionnares For evaluation of the level of knowledge about radiation protection we developed a simple questionnaire and gave them to staff from the departments of anesthesiology, surgery, and radiology (Fig. 6 on page 17). The questions were: Age and gender? (Fig. 7 on page 18) Profession? (Fig. 8 on page 19) How often are you present during interventions? (Fig.9 on page 20) How often is your presence unavoidable? (Fig. 10 on page 21) Which is the major location of your presence? (Fig. 11 on page 22) Point at which you expect the highest exposure? (Fig. 12 on page 23) Point at which you expect the lowest exposure? (Fig. 13 on page 24) Page 11 of 31

12 8. How often could you move to point of lowest exposure when radiation is applied? (Fig. 14 on page 25) 9. What is your level of knowledge about radiation protection? (Fig. 15 on page 26) 10. Would floor marks be useful to show areas of high exposure? (Fig. 16 on page 27) The analysis of the questionnaire showed that most of the staff is at a younger age and most of the female employees are in their reproductive age. Only a minority is present more than once a week. Nevertheless, dose will accumulate over time. Most of the staff thinks that presence during interventions can be limited and is unavoidable in only a minority of cases, depending on the profession (interventionalists need to stay in the room most of the time). Over 94% of the staff knows where the highest exposure can be expected. About 78% of the staff correctly identified the places with lowest exposure, which is a good amount but less than in the prior question. More 66% of the people think that moving to a place with less exposure is possible in 50% and more. However from personal experiece before the questionnaire was handed out, we observed that the staff stayed at one location for the whole intervention without seeking cover. A large majority of staff has only basic or less knowledge about radiation protection which strongly indicates the need for continuous education and information about this topic. Almost all of the persons asked stated that floor marks on the floor would help to identify the areas with high exposure. 3. Floor marks During the installation of the CT at our institution, gray floor marks were installed to show the isodose curve with the highest exposure (Fig. 17 on page 28). These marks were introduced to the staff with an oral presentation similar to this exhibit. To our experience, the floor marks help the staff that is not always working in the radiology department to remember the locations with high exposure and to quickly find a place with low exposure. Images for this section: Page 12 of 31

13 Fig. 1: Image was taken during a vertebroplasty showing typical location of staff. Page 13 of 31

14 Fig. 2: This scheme represents the CT room with the installed device. Points that are relevant for location of the staff are marked as follows: 1. Next to gantry (potential cover) 2. Lateral and sligthly behind gantry (potential cover) 3. In front of the bore (interventionalist) 4. Point far awy from gantry (potential cover) 5. Behind the bore (anesthesiology) Page 14 of 31

15 Fig. 3: Left side: Floor markers at the points shown in Fig. 2. Right side: Anthropomorphic phantom in the gantry bore. Page 15 of 31

16 Fig. 4: Dose measurements were performed at the specified points in the room without and with apron in front of the dosimeters. Page 16 of 31

17 Fig. 5: Results from dose measurement in the CT room. Page 17 of 31

18 Fig. 6: Number and profession of persons that returned the questionnaire. Page 18 of 31

19 Fig. 7: Question 1 Page 19 of 31

20 Fig. 8: Question 2. Page 20 of 31

21 Fig. 9: Question 3. Page 21 of 31

22 Fig. 10: Question 4. Page 22 of 31

23 Fig. 11: Question 5. Page 23 of 31

24 Fig. 12: Question 6. Page 24 of 31

25 Fig. 13: Question 7. Page 25 of 31

26 Fig. 14: Question 8. Page 26 of 31

27 Fig. 15: Question 9. Page 27 of 31

28 Fig. 16: Question 10. Page 28 of 31

29 Fig. 17: During the installation of the CT device, marks were placed on the floor to show the isodose curve with the highest exposure. Page 29 of 31

30 Conclusion Analysis of the questionnaires has shown that radiation protection is a very important issue (young staff, only limited knowledge). Regular training and education has to be done to improve level of knowledge. Dose measurements are quite useful to illustrate how exposure varies at specified points (over 250-fold). Floor marks can help the staff to avoid or at least lower their personal exposure. Personal Information References 1. Al-Haj AN, Lobriguito AM, Lagarde CS. Occupational doses during the injection of contrast media in paediatric CT procedures. Radiat Prot Dosimetry 2003; 103: Komemushi A, Tanigawa N, Kariya S, Kojima H, Shomura Y, Sawada S. Radiation exposure to operators during vertebroplasty. J Vasc Interv Radiol 2005; 16: Nawfel RD, Judy PF, Silverman SG, Hooton S, Tuncali K, Adams DF. Patient and personnel exposure during CT fluoroscopy-guided interventional procedures. Radiology 2000; 216: Paulson EK, Sheafor DH, Enterline DS, McAdams HP, Yoshizumi TT. CT fluoroscopy-guided interventional procedures: techniques and radiation dose to radiologists. Radiology 2001; 220: Theumann NH, Verdun FR, Valley JF, Capasso P, Schnyder P, Meuli RA. Radiation doses delivered to radiologists during contrast-enhanced helical-ct examinations. Eur Radiol 1999; 9: Fujibuchi T, Kato H, Hashimoto M, Ochi S, Yanagawa N, Morita F. [Shielding effect of protective seats during CT examination]. Nippon Hoshasen Gijutsu Gakkai Zasshi 2004; 60: Irie T, Kajitani M, Itai Y. CT fluoroscopy-guided intervention: marked reduction of scattered radiation dose to the physician's hand by use of a lead plate and an improved I-I device. J Vasc Interv Radiol 2001; 12: Page 30 of 31

31 8. Neeman Z, Dromi SA, Sarin S, Wood BJ. CT fluoroscopy shielding: decreases in scattered radiation for the patient and operator. J Vasc Interv Radiol 2006; 17: Heyer CM, Peters S, Lemburg S, Nicolas V. [Awareness of radiation exposure of thoracic CT scans and conventional radiographs: what do non-radiologists know?]. Rofo 2007; 179: Page 31 of 31