Abstract
Radiation injury can occur after chronic total occlusion intervention, hence strategies to minimize radiation exposure are critical and should be applied from the outset of the procedure. The total air kerma (AK) radiation exposure should be carefully monitored throughout the case and the operator should consider stopping the procedure if crossing is not achieved after 7–10 Gy. Low frame rate (6 or 7.5 frames per second) and low magnification (25 cm) fluoroscopy should be strongly considered. Collimation should be employed whenever possible and the image intensifier should be rotated to minimize the exposure of each area of the skin. Additional shielding should be used to minimize radiation scatter. Patients who receive >5 GyAK dose should be educated about the potential adverse effects of radiation and carefully followed up to detect any radiation skin injury.
Keywords
Air kerma, Chronic total occlusion, Fluoroscopy, Gray, Image intensifier, Radiation, Shielding, Skin injury
Radiation skin injury ( Fig. 10.1 ) is a rare complication of any invasive cardiac procedure, but is more likely to occur in the setting of complex procedures, such as chronic total occlusion (CTO) percutaneous coronary intervention (PCI), where large doses of radiation are often used. Radiation skin injury can lead to severe consequences for the patient, such as painful, nonhealing ulcers that may require months or even years to heal and in some cases may even require surgical debridement and plastic reconstruction.
A plan for radiation dose management from the outset of all PCI cases, especially CTO PCI, is essential. Such a plan will not only lead to a lower radiation dose to the patient, but it will also reduce physician and staff dosing. Interventional cardiologists and staff are exposed to ionizing radiation on a daily basis over many years, which can increase their risk for developing cancer (such as, but not limited to, left-sided brain tumors ), cataracts, and other ailments, as well as orthopedic problems associated with protective garments.
Despite the obvious benefits in of limiting radiation exposure, observations from multiple cardiac catheterization laboratories have shown that sound radiation management practices are infrequently implemented, although progress has been documented by some programs. The goal of this chapter is to provide simple and practical tips and tricks for reducing both patient and operator radiation exposure.
10.1
Why Radiation Management Is Important
- 1.
To prevent radiation injury to the patient.
- 2.
To prevent radiation injury to the operator and the cardiac laboratory staff.
- 3.
To prevent medico–legal consequences, since significant radiation exposure (>15 Gy air kerma (AK) dose) is considered a sentinel event by the Joint Commission for Hospital Accreditation.
- 4.
Because there is increasing public and medical community concern about radiation exposure during medical procedures, regarding an individual procedure as well as the lifelong cumulative radiation exposure of patients.
10.2
Essentials of Radiation Dose Management
It is recommended that operators wishing to develop a CTO (or any complex PCI) program consult with their institution’s radiation officers to implement strict radiation management protocols and safe radiation management practices. It is then essential that these protocols, in conjunction with appropriate established thresholds, be incorporated into the cath lab quality assurance/quality improvement program.
There are two ways to minimize radiation during CTO PCI procedures:
- 1.
By acquiring the skill sets and expertise to perform safe and efficient CTO PCI procedures (as described throughout this text).
- 2.
By implementing safe radiation management practices.
The rest of this chapter focuses on radiation management practices.
- 1.
Dose Assessment: Understand how radiation is measured in the cardiac cath lab and which radiation measure should be looked at .
Assessment of radiation dose in the cardiac cath lab is much more than fluoroscopy time (FT, measured in minutes). FT has several limitations, the most obvious of which is its failure to include cine imaging; hence, FT alone is not adequate to assess patient radiation dose. The actual administered radiation dose depends on many other factors, such as the weight of the patient, the use of collimation, the positioning of the table and image intensifier, and the imaging angles. For this reason, since 2006, all fluoroscopic equipment sold in the United States have additional parameters to measure patient dose that are recorded and displayed during the procedure.
There are two standard parameters reported on interventional fluoroscopic equipment: cumulative AK at the interventional reference point (measured in Gray [Gy]) and dose area product (DAP, measured in Gycm 2 , also called AK area product) ( Fig. 10.2 ). DAP is used to monitor the potential for genetic defects or cancer risk over time, called stochastic effects, and is not used for intraprocedural radiation dose monitoring in the United States.
Figure 10.2
Screenshot from an X-ray machine screen, highlighting the fluoroscopy frames per second ( yellow box : 15 fps in (A) vs. 7.5 fps in (B)). Also, the air kerma (494 mGy or 0.494 Gy) and the dose area product radiation dose are highlighted .
The AK dose is the number that the CTO operator should constantly monitor to determine the risk that the patient will develop radiation skin injury and adjust the procedural plan accordingly. Total AK is the procedural cumulative X-ray energy delivered to air at the interventional reference point (i.e., 15 cm on the X-ray tube side of isocenter), the point at which the primary X-ray beam intersects with the rotational axis of the C-arm gantry. Kerma stands for Kinetic Energy Released in Matter. Although the AK dose is an approximation of the actual radiation that the patient receives during a procedure, it is a far better and physiologically relevant index as compared with FT. Deterministic radiation effects, such as skin injury, correlate directly with the AK dose to a particular skin area ( Fig. 10.1 ).
The following AK dose thresholds are important to remember :
>5 Gy : below this threshold skin injury is unlikely to occur.
>10 Gy : skin injury is likely, requiring physicist assessment of the case.
>15 Gy : considered a sentinel event by the Joint Commission for Hospital Accreditation and requires reporting to the regulatory authorities in the United States.
- 2.
Laboratory Environment
All cardiac cath labs should have a radiation safety program with active participation of physicians, staff, and physicists with reports regularly reviewed in the cath lab QA program. All interventional cardiologists should apply two basic principles of radiation protection to their practice: reduce radiation exposure to as low as reasonably achievable (ALARA), and ensure procedure justification, such that no patient receives radiation without potential benefit.
Although only certain states mandate fluoroscopy training, it is important that everyone receives radiation dose management and safety training commensurate to their responsibilities. The National Council on Radiation Protection recommends both didactic and hands-on training. The didactic program should include initial training with periodic updates covering the topics of radiation physics and safety. Hands-on training should be provided for newly hired operators and all operators on newly purchased equipment.
It is the individual’s responsibility to wear a dosimeter. Although a single dosimeter worn outside the collar can be used, two properly worn dosimeters—one at the waist under, and one at the collar outside, the protective garment—provide a better reflection of effective dose. However, one dosimeter worn correctly at collar height externally is better than two worn incorrectly. Protective garments stop approximately 95% of the scatter radiation. Radiation glasses must fit properly, have 0.25-mm lead equivalent protection, and have additional side shielding. Ceiling-mounted and below-table shielding are also effective; both should be used routinely.
Current fluoroscopic X-ray systems offer features for dose management including frame rate adjustment, virtual collimation, last image hold, X-ray store, and real-time dose display. Image quality is a function of multiple patient, procedural, and equipment variables. As a general rule, image quality and radiation dose are tightly woven with higher dose often improving image quality: achieving the acceptable image quality for a procedure at the lowest dose is key. Automatic dose rate controls increase dose for a specific patient size in a specific projection to achieve adequate image quality. Knowing the equipment and working with a qualified physicist are essential for dose optimization. Also several X-ray equipment vendors are willing to work with hospitals to optimize the settings of the installed systems to reduce radiation dose.
- 3.
Procedure-Based Radiation Dose Management
Table 10.1 provides a procedure-based dose management outline. Preprocedure planning is an essential component of radiation dose management. It is important to detect factors that place patients at high risk for radiation-induced skin injury, such as obesity or recent fluoroscopic procedures within the previous 30–60 days. Informed consent for CTO PCI should include radiation safety information.
Table 10.1
Procedure-Based Case Management of Radiation Dose
- I.
Preprocedure
- A.
Radiation safety program for catheterization lab
- 1.
Dosimeter use, shielding, training/education
- 1.
- B.
Imaging equipment and operator knowledge
- 1.
On-screen dose assessment (air kerma, dose area product)
- 2.
Dose saving: Store fluoroscopy, adjustable pulse and frame rate and last image hold
- 1.
- C.
Preprocedure dose planning
- 1.
Assess patient and procedure, including patient’s size and lesion(s) complexity; examine patient for potential skin injury from prior high-dose cases
- 1.
- D.
Informed patient with appropriate consent
- A.
- II.
Procedure
- A.
Limit fluoroscopy: Step on pedal only when looking at screen
- B.
Limit cine: Store fluoroscopy when high image quality is not required
- C.
Limit magnification, frame rate, steep angles
- D.
Use collimation and filters to the fullest extent possible
- E.
Vary tube angle when possible to change skin area exposed
- F.
Position table and image receptor: X-ray tube too close to patient increases dose; high image receptor increases scatter
- G.
Keep patient and operator body parts out of field of view
- H.
Maximize shielding and distance from X-ray source for all personnel
- I.
Manage and monitor dose in real time from beginning of case
- A.
- III.
Postprocedure
- A.
Document radiation dose in records (fluoroscopy time, K a,r , P KA )
- B.
Notify patient and referring physician when high dose delivered
- 1.
K a,r > 5 Gy, chart document; inform patient; arrange follow up
- 2.
K a,r > 10 Gy, qualified physicist should calculate skin dose
- 3.
PSD >15 Gy, Joint Commission Sentinel Event
- 1.
- C.
Assess and refer adverse skin effects to appropriate consultant
- A.
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