ABSTRACT
On 28th August 2007 the Cardiac and Cardiothoracic departments at King’s College Hospital London began jointly providing a trans-catheter aortic valve intervention (TAVI) service. This service provides treatment for aortic stenosis in high risk patients turned down for conventional aortic valve surgery. Due to the treatment being new and involving a multi-disciplinary team not all of whom are used to working with radiation, we decided to complete a radiation dose audit looking at the radiation doses received by various staff groups in the laboratory during procedures. The main finding was the much higher leg doses that were being received by staff standing on the left side of the table (from the patients’ perspective), compared to staff standing on the patients’ right.
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BACKGROUND
Aortic stenosis can be caused by calcific sclerosis, scarring caused by rheumatic fever when young, and bicuspid aortic valve disease (1). Calcific aortic stenosis is most common in patients over 60 years old, but symptoms often do not appear until 70 or 80 years of age. Symptoms can include angina, feeling faint, dizziness, fatigue, heart palpitations and swollen ankles/feet. Echocardiography is the gold standard assess tool to confirm diagnosis and severity of the disease. Once diagnosed, and if turned down for conventional valve surgery, patients being worked up for treatment also have an aortogram, and both a coronary and aorto-iliac angiogram. They also have a CT scan.
There are two methods of insertion for the Edwards Lifesciences valves used at King’s College Hospital. The transfemoral approach is performed by a Cardiologist with the assistance of a Cardiac Surgeon. The new valve is inserted via the iliac artery and aorta (see above left). A transapical approach is performed by a Cardiac Surgeon with assistance from a Cardiologist (see above right).
Either approach presents problems with regards to radiation protection due to both the number of staff that are required to be in the lab during the procedure, and the close proximity some of them need to be to the patient undergoing the procedure.
With a trans-femoral approach, the Cardiologist who is leading the procedure can do all of his work from the level of the patient’s groin, allowing him to keep a greater distance between himself and the x-ray beam than can the Cardiothoracic Surgeon when leading on a trans-apical approach, due to the need to access the patients’ heart direct to introduce the valve catheter with the trans-apical approach.
With both trans-apical and trans-femoral procedures there is at least one Echo Specialist performing a trans-oesophageal echo to produce both 2D and 3D imaging to help position the new valve in the most optimal position. Due to equipment design they also have to stand on the patients left in very close proximity to the primary beam.
Due to the fact that trans-catheter aortic valve insertions (TAVI’s) were a new procedure for us at King’s, it was decided to do a radiation dose audit to highlight any dose issues with the procedure, and get some baseline measurements. After advice from a Medical Physicist we decided to do the audit over 10 procedures, 5 trans-apical and 5 trans-femoral. The following staff were monitored as described below:
CARDIOLOGIST: Whole body (WB), leg, left ring finger (LR), right ring finger (RR).
CARDIOTHORACIC SURGEON: WB, leg, LR, RR.
ECHO SPECIALIST: WB, leg, LR, RR.
CARDIOLOGY SCRUB NURSE: WB.
SURGERY SCRUB NURSE: WB.
ANAESTHETIST: WB.
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DISCUSSION
Perhaps the two standout readings when analysing the doses are the Surgeon and Echo leg readings of 6.73mSv and 7.03mSv respectively. We have always had under-table lead shielding in the labs on the table side to the patients right, but never on the table side to the patients left. Both the Surgeon and the Echo Specialist stand at the side of the table to the patients left. We now have under-table shielding for the left side of the table that we fit for these procedures.
Of note is that the Surgeon RR reading is 3.17mSv and LR 1.87mSv. This is more than the Cardiologist RR 0.71mSv and LR 1.47mSv. This is in part due to the Surgeons being in closer proximity to the primary beam that the Cardiologists whilst doing procedures, due to the access point of the catheter for respective procedures (femoral artery for Cardiologists, apex of heart for Surgeons).
Both Echo ring readings (LR 1.31 mSv, RR 1.43mSv) were higher than the Cardiologist RR reading of 0.71mSv. This is in part due to the need to manipulate the echo probe in close proximity to the primary beam, and also to the lack of under table lead shielding on the table at that time of the trial.
The Cardiologist WB dose was higher than expected at 4.82mSv. This is significantly higher than both Surgeon and Echo WB readings of 0.65mSv and 0.28mSv. At the end of one of the cases it was noticed that the Cardiologist had the WB badge tucked into the front pocket of his lead coat. The pocket itself is not lead protected. It is considered that this practice (unsure for how many cases) was the reason for the aberrant reading.
Other dose readings showed no significant dose was being received by other staff in the room during the procedure.
CONCLUSIONS
The new TAVI procedures being performed are being done with due consideration to safe radiation protection practices.
The leg doses being received on the left side of the table should reduce significantly now there is under-table lead shielding fitted to both sides of the table during these procedures, although even the study levels would still come in under the annual permissible limits
Finger doses being received are well under national annual limits, but Cardiologists, Surgeons, and Echo staff should give due consideration to the primary beam when operating in the vicinity of it.
RECOMMENDATIONS
The study should be re-run now the new lead shielding is in place to ensure leg doses have reduced.
All centres that are performing TAVI Procedures should have under-table shielding fitted to both sides of the x-ray couch.
Appropriate radiation protection advice and training should be given to all staff involved with the procedures whom have otherwise not had training.
REFERENCES
Edwards Lifesciences
THE LEAFLET
Special Referral Edition: For Physicians Treating Aortic Stenosis January 2008
THANKS
To King’s College Hospital NHS Trust Radiation Protection Advisory Dr Neil Lewis and his team in the Medical Physics Department for advice and guidance both before, during and after the study.
For all the staff who faithfully wore the respective monitoring badges during the trial.
