by Dr.G.Justin Paul, Professor of Cardiology, Madras Medical College
X-rays are electromagnetic radiation, travelling in the speed of light in straight lines with high penetrating capacity, ionising the tissues along the path leading to harmful effects. These are of two types. Deterministic effects are related to the dose of radiation [eg: ocular and skin effects]. Stochastic effects are not directly dose related [eg: cancers, genetic defects]
High voltage direct current from a step up transformer, generates electrons from the cathode inside the Xray tube. These electrons travel in high velocity towards a rotating tungsten anode also inside the Xray tube, causing them to produce X-rays. These X-rays pass through filters and collimation blades and fall on the patient. Some of the X-rays are absorbed contributing to patient dose. Some X-rays are scattered contributing to staff radiation. Rest of them travel and reach the flat panel detector contributing to image formation.
Radiation exposure in the ambient air is measured in terms of air KERMA and is displayed in the monster in milligrays [mGy]. Tissue dose or absorbed dose is the dose the patient absorbs. The effective dose is the radiation dose exposure to the health care worker [measured in millisieverts]
Basic Principles of Radiation Protection: There are three basic principles of radiation safety
1.Justifiable exposure demands that the benefit of use of radiation in a given setting should outweigh the harm associated with it.
2. ALARA principle suggests that radiation exposure should be as low as reasonable achievable, to achieve a safe and successful procedure. ALARA principle is achieved by three basic tenets
- Time: As low time of radiation as possible
- Distance: As far away from the radiation source as possible
- Shielding: Shielding the patient and the staff from the radiation as much as possible
3.Dose limits: The permitted dose limits for the patient, the operator and the staff should be watched and never be exceeded.
The Ten Commandments of Radiation Safety
The practice of the ALARA principle is possible by following the ten commandments of radiation safety as mentioned below.
- Press the foot pedal as little as possible, only when the primary operators eye is actively looking at the fluoroscopy monitor. Do all steps that can be done with out radiation, before pressing the foot pedal.
- Collimate the Xray beam: Collimation reduces the volume of the irradiated tissue to the area of interest only, reducing the patient dose and scatter radiation, thus reducing the operator dose too. Perform collimation on the last image hold.
- Stay away from the patient and the X-ray tube. Radiation dose decreases in proportion to the square of the distance from the source. Staying outside the lab if our presence is not required and staying close to the walls, if we need to be inside the lab, are good principles to follow.
- Shield the patient and the operator and staff as much as possible. Use lead apron, thyroid collar, eye glasses, head shield, Roof shield, foot shield etc
- Keep the flat panel detector as close to the patient as possible. This will reduce the scatter and improve the image clarity.
- Keep the table as away [high] from the Xray tube as possible, as this will reduce the patient skin dose and thus the scatter.
- Avoid steep angles, as they lengthen the tissue path, increase the volume of irradiated tissues and increase scatter.
- Avoid magnification / zoom as they increase the tissue radiation dose.
- DSA has100 times more radiation and acquisition mode [cine] has 10 timed more radiation than fluoroscopy. So avoid DSA and acquisition mode.
- Monitor the radiation exposure of every health care worker with TLD badges.
Following these simple “10 COMMANDMENTS” in every catheterisation laboratory will contribute significantly in preventing radiation hazards and improving the patient and the staff health.
The author, Dr G Justin Paul is Professor of Cardiology at Madras Medical College, Chennai, He is presenting on the topic Radiation safety in Catheterisation laboratory: An often forgotten Issue at India Live 208