Good practices in interventional procedures

Frequently asked questions by the health professionals

» How can I know patient dose while using the C-arm in an operating theatre? 
» Should the X-ray tube be positioned closer to the patient or further away from the patient during fluoroscopy? 
» Does a patient’s physique have an effect on radiation dose to the patient and staff? 
» How effective is a reduction in fluoroscopy time in reducing dose to the patient and staff? 
» Is there a difference between a single long fluoroscopy and several shorter fluoroscopies with same total doses? 
» How should I select the pulse frequency in pulsed fluoroscopy? 
» Does the use of shielding have an effect on a patient’s radiosensitive organ dose? 
» Should termination of pregnancy be considered after a fluoroscopically guided procedure? 
» What is the magnitude of patient doses associated with fluoroscopically guided procedures? 
» Key points to remember in patient dose management in fluoroscopy. 

» How can I know patient dose while using the C-arm in an operating theatre?

By having a dose meter installed. The C-arm fluoroscopy systems commonly used in operating theatres might not be equipped with patient dose monitoring capabilities. In view of the high doses involved in many fluoroscopic procedures, users of such equipment should insist on having patient dose monitoring device retro-fitted after the purchase of a new unit or acquire systems equipped with a dose measuring system. Regulations in many countries do require this. When installed, these systems will provide real time display of dose while the procedures are being performed. A qualified and experienced medical physicist will be able to provide a meaningful interpretation of dose.

» Should the X-ray tube be positioned closer to the patient or further away from the patient during fluoroscopy?

As further away as possible. Increasing the distance of the X-ray tube from the patient means that the dose to the patient’s skin will decrease according to the inverse square law. On the other hand, placing the image intensifier (detector) as close to the patient as possible maximizes the intensity of radiation intercepted by the detector, resulting in reduction of radiation intensity produced by the X-ray source. It also leads to more efficient image acquisition and a possible overall decrease in fluoroscopy time and subsequent dose reduction for the patient. In conclusion, the operator should increase the distance of the X-ray tube from the patient as much as practicable and decrease the distance of imaging detector by as much as practically possible.

» Does a patient’s physique have an effect on radiation dose to the patient and staff?

Yes. All fluoroscopy systems which operate in automatic exposure control (AEC) mode require that a certain amount of radiation reaches the detector in order to produce clinically useful images. Most units are equipped with automatic exposure (or brightness) control (ABC) systems. When a thicker patient is positioned in the path of the X-ray beam, the AEC system increases the exposure factors (kV, mA) in order to compensate for the increased attenuation in the patient’s body and conversely the exposure factors decrease when a slim patient or thinner body part is in the beam. This could result in higher radiation dose and elevated risk of radiation injury to the skin of thicker patients. Dose to the staff would also increase as a result of an increase in exposure factors.

» How effective is a reduction in fluoroscopy time in reducing dose to the patient and staff?

Very effective. Fluoroscopy time is the easiest parameter to perceive and control. Minimization of fluoroscopy time has been proven to be one of the most effective ways of reducing radiation dose to the patient and staff during fluoroscopy. Experience has shown that a substantial reduction in patient dose may be achieved by limiting the fluoroscopy time. However, it is important to note that fluoroscopy time is not the only parameter which reduces the dose to the patient. Dose also depends on other factors such as thickness of the imaged body part, field of view, pulse frequency and dose level of fluoroscopy employed. The radiation exposure of the patient and staff are also dependent on cine images or frame acquisitions.

In some instances the contribution from fluoroscopy and from frame acquisitions may be almost equal. Reducing patient dose can also lead directly to a reduction in staff dose.

» Is there a difference between a single long fluoroscopy and several shorter fluoroscopies with same total doses?

No and yes. No, with respect to the total radiation induced cancer risk. Yes, with respect to skin injuries or other tissue reactions. A dose received in shorter time is more effective in causing tissue reactions than the same dose protracted in time. This is due to the fact that when dose is received during a longer period of time tissue cells have the time to repair themselves through cellular repair mechanisms between successive irradiations.

» How should I select the pulse frequency in pulsed fluoroscopy?

In contrast to continuous fluoroscopy, pulsed fluoroscopy aims to reduce the dose to patients and staff by using short pulses of radiation. The pulse frequency should be as low as possible provided that it is adequate to achieve the clinically desired results. Typically, for most non cardiac procedures, a pulse rate of 10 pulses/s or less should be adequate.

» Does the use of shielding have an effect on a patient’s radiosensitive organ dose?

The use of shielding in fluoroscopy can be effective, but for procedures performed in operating theatres the feasibility of using patient shielding is a practical problem. Shielding, wherever possible is effective for protection of the patient’s radio-sensitive organs, such as the breast, gonads, eyes and thyroid. However, scattered radiation arising and propagating inside the patient’s body constitutes the main source of radiation dose to organs. Internal scatter can be managed by good technique.

» Should termination of pregnancy be considered after a fluoroscopically guided procedure?

Not invariably unless the primary beam passes through the fetus. If the X-ray beam is directed at body parts other than pelvic and lower abdomen region, it is unlikely that the dose received by the fetus would approach a level at which a termination would be considered (i.e. 100 mGy). If the primary beam irradiates the chest or upper abdomen region, only scattered radiation from within the patient’s body, mostly internal scatter, will reach the fetus. Estimates in such situations indicate that fetal radiation dose can be kept fairly low, typically below 1 mSv, with technique optimization.

However, the exposure of pregnant women to radiation is always a concern when the primary beam approaches the fetal area. In such situations, where the fetus is in or near the primary beam, the procedure should only be performed if this is essential for managing the patient’s condition. When such interventions are clinically justified on an individual basis, every optimization effort should be made to achieve the desired clinical result with the least possible exposure of the fetus. Fetal dose should be estimated as accurately as possible with the help of a medical physicist or radiation protection specialist; similarly before and after the procedure. The question of termination of pregnancy may not arise in a well planned and executed procedure. However, in situations of inadvertent fetal exposure, the considerations described in Pregnancy and Radiation Protection in Diagnostic Radiology should be taken into account.

» What is the magnitude of patient doses associated with fluoroscopically guided procedures?

Patient doses during fluoroscopically guided anaesthetic procedures such as epidural injections have been reported to range between 0.08 and 0.15 mSv per minute of fluoroscopy when pulsed fluoroscopy of 3-15 pulses per second is used. Typical dose values that might be imparted to patients during procedures in various operating theatres are given below. The doses are tabulated in terms of the mean effective dose, the mean dose area product (DAP) and the equivalent number of chest radiographs.

Table: Mean effective doses and DAP values from vascular surgical procedures

Read more:

• Mean effective doses and DAP values from urological procedures
• Mean effective doses and DAP values from orthopaedic procedures 

» Key points to remember for patient dose management in fluoroscopy

• Know your equipment;
• Maximize the distance of the X-ray tube from the patient to the extent possible;
• Minimize the distance of the detector from the patient; 
• Minimize the fluoroscopy time (FT). Keep a record of FT for each patient; 
• Use the lowest frame rate consistent with image quality; 
• Be aware that oblique projections and lateral views will result in higher patient dose; 
• Vary the position where the beam enters the patient; Avoid irradiating the same part of skin by using rotation;
• Keep a record of the patient dose (kerma area product (KAP) and cumulative air kerma (CAK) and skin dose); 
• Minimize the number frames of cine runs or frames (if applicable); 
• Do not use acquisition mode for fluoroscopy (if applicable); 
• Avoid using a large field of view or magnification; 
• Be aware that skin injury can happen when KAP>300 Gy.cm2 or skin dose>2 Gy or CAK>3 Gy. Advise the patient to keep a watch on skin and inform you in case of skin reaction.

For more information on techniques to minimize patient dose during fluoroscopy, click here.

References:

• Schmid, G., Schmitz, A., Borchardt, D., Effective Dose of CT- and Fluoroscopy-Guided Perineural/Epidural Injections of the Lumbar Spine: A Comparative Study, Cardiovasc Intervent Radiol 29 (2005) 84–91. 
• Weerakkody, R.A., Walsh, S.R., Cousins, C. et al., Radiation exposure during endovascular aneurysm repair, Br. J. Surg. 95 (2008) 699 – 702. 
• Geijer, H., Larzon, T., Popek, R., et al., Radiation exposure in stent-grafting of abdominal aortic aneurysm, Br. J. Radiol. 78 (2005) 906-912. 
• Storm, E.S., Miller, D.L., Hoover, L.J., et. al., Radiation doses from venous access procedures, Radiology 238 (2006) 1044-1050. 
• Miller, D.L., MD, Balter, S., Cole, P.E., et al., Radiation Doses in Interventional Radiology Procedures: The RAD-IR Study Part II: Skin Dose, J. Vasc. Interv. Radiol. 14 8 (2003) 977–990. 
• NATIONAL COUNCIL ON RADIATION PROTECTION AND MEASUREMENTS, 2007. Ionizing Radiation Exposure of the Population of the United States, Report 160, Bethesda, MD (2009).