Louis K. Wagner

Potential Biological Effects Following High X-ray Dose Interventional Procedures

Some interventional procedures can result in very high x-ray doses. Potential biological effects of high x-ray doses are reviewed. Deterministic and stochastic effects in skin, bone, parotid glands, and lung are discussed. Threshold doses for the effects and relevant dosimetric principles are addressed. General principles for minimizing the potential for these effects are presented. Knowledge about these effects and the means to minimize radiation dose can assist the physician in the care of patients undergoing lengthy invasive radiologic procedures.

Fluoroscopically guided interventional procedures: a review of radiation effects on patients' skin and hair.

Most advice currently available with regard to fluoroscopic skin reactions is based on a table published in 1994. Many caveats in that report were not included in later reproductions, and subsequent research has yielded additional insights. This review is a consensus report of current scientific data. Expected skin reactions for an average patient are presented in tabular form as a function of peak skin dose and time after irradiation. The text and table indicate the variability of reactions in different patients. Images of injuries to skin and underlying tissues in patients and animals are provided and are categorized according to the National Cancer Institute skin toxicity scale, offering a basis for describing cutaneous radiation reactions in interventional fluoroscopy and quantifying their clinical severity. For a single procedure performed in most individuals, noticeable skin changes are observed approximately 1 month after a peak skin dose exceeding several grays. The degree of injury to skin and subcutaneous tissue increases with dose. Specialized wound care may be needed when irradiation exceeds 10 Gy. Residual effects from radiation therapy and from previous procedures influence the response of skin and subcutaneous tissues to subsequent procedures. Skin irradiated to a dose higher than 3-5 Gy often looks normal but reacts abnormally when irradiation is repeated. If the same area of skin is likely to be exposed to levels higher than a few grays, the effects of previous irradiation should be included when estimating the expected tissue reaction from the additional procedure.

Fetal dose from radiotherapy with photon beams: Report of AAPM Radiation Therapy Committee Task Group No. 36

Approximately 4000 women per year in the United States require radiotherapy during pregnancy. This report presents data and techniques that allow the medical physicist to estimate the radiation dose the fetus will receive and to reduce this dose with appropriate shielding. Out-of-beam data are presented for a variety of photon beams, including cobalt-60 gamma rays and x rays from 4 to 18 MV. Designs for simple and inexpensive to more complex and expensive types of shielding equipment are described. Clinical examples show that proper shielding can reduce the radiation dose to the fetus by 50%. In addition, a review of the biological aspects of irradiation enables estimates of the risks of lethality, growth retardation, mental retardation, malformation, sterility, cancer induction, and genetic defects to the fetus.

Managing Radiation Use in Medical Imaging: A Multifaceted Challenge

This special report aims to inform the medical community about the many challenges involved in managing radiation exposure in a way that maximizes the benefit-risk ratio. The report discusses the state of current knowledge and key questions in regard to sources of medical imaging radiation exposure, radiation risk estimation, dose reduction strategies, and regulatory options.

Clinical radiation management for fluoroscopically guided interventional procedures.

The primary goal of radiation management in interventional radiology is to minimize the unnecessary use of radiation. Clinical radiation management minimizes radiation risk to the patient without increasing other risks, such as procedural risks. A number of factors are considered when estimating the likelihood and severity of patient radiation effects. These include demographic factors, medical history factors, and procedure factors. Important aspects of the patients medical history include coexisting diseases and genetic factors, medication use, radiation history, and pregnancy. As appropriate, these are evaluated as part of the preprocedure patient evaluation; radiation risk to the patient is considered along with other procedural risks. Dose optimization is possible through appropriate use of the basic features of interventional fluoroscopic equipment and intelligent use of dose-reducing technology. For all fluoroscopically guided interventional procedures, it is good practice to monitor radiation dose throughout the procedure and record it in the patients medical record. Patients who have received a clinically significant radiation dose should be followed up after the procedure for possible deterministic effects. The authors recommend including radiation management as part of the departmental quality assurance program.

Management of Patient Skin Dose in Fluoroscopically Guided Interventional Procedures

PURPOSE To simulate dose to the skin of a large patient for various operational fluoroscopic conditions and to delineate how to adjust operational conditions to maintain skin dose at acceptable levels. MATERIALS AND METHODS Patient entrance skin dose was estimated from measurement of entrance air kerma (dose to air) to a 280-mm water phantom for two angiographic fluoroscopes. Effects on dose for changes in machine floor kVp, source-to-skin distance, air gap, electronic magnification, fluoroscopic dose rate control settings, and fluorographic dose control settings were examined. RESULTS Incremental changes in operational parameters are multiplicative and markedly affect total dose delivered to a patients skin. For long procedures, differences in doses of 8 Gy or more are possible for some combinations of operational techniques. CONCLUSIONS Effects on skin dose from changes in operational parameters are multiplicative, not additive. Doses in excess of known thresholds for injury can be exceeded under some operating conditions. Adjusting operational parameters appropriately will markedly reduce dose to a patients skin. Above all other operational factors, variable pulsed fluoroscopy has the greatest potential for maintaining radiation exposure at low levels.

Quality improvement guidelines for recording patient radiation dose in the medical record.

From the Department of Interventional Radiology (D.L.M.), National Naval Medical Center, Bethesda, Maryland; Department of Medicine (S.B.), Lenox Hill Hospital, New York; Department of Radiology (L.K.W.), University of Texas Houston Medical School, Houston, Texas; Department of Radiology (J.F.C.), SUNY–Upstate Medical University, Syracuse, New York; Section of Vascular and Interventional Radiology (T.W.I.C.), Department of Radiology, Hospital of the University of Pennsylvania; Department of Radiology (R.B.T.), Children’s Hospital of Philadelphia, Philadelphia; Department of Radiology (D.S.), Reading Hospital and Medical Center, Reading, Pennsylvania; Department of Radiology (C.D.N.), Inova Mount Vernon Hospital; Department of Radiology (K.S.R.), Inova Alexandria Hospital, Alexandria, Virginia; Radiology Associates of Central Florida (M.S.S.) Leesburg, Florida; and Department of Radiology (T.L.S.), Marshfield Clinic, Marshfield, Wisconsin. Received January 23, 2004; accepted January 23. Address correspondence to SIR, 10201 Lee Highway, Suite 500, Fairfax, VA 22030.

Radiation injuries after fluoroscopic procedures.

Fluoroscopically guided diagnostic and interventional procedures have become much more commonplace over the last decade. Current fluoroscopes are easily capable of producing dose rates in the range of 0.2 Gy (20 rads) per minute. The dose rate often changes dramatically with patient positioning and size. Most machines currently in use have no method to display approximate patient dose other than the rough surrogate of total fluoroscopy time. This does not include patient dose incurred during fluorography (serial imaging or cine runs), which can be considerably greater than dose during fluoroscopy. There have been over 100 cases of documented radiation skin and underlying tissue injury, a large portion of which resulted in dermal necrosis. The true number of injuries is undoubtedly much higher. The highest dose procedures are complex interventions such as those involving percutaneous angioplasties, stent placements, embolizations, and TIPS. In some cases skin doses have been in excess of 60 Gy (6000 rads). In many instances the procedures have been performed by physicians with little training in radiation effects, little appreciation of the radiation injuries that are possible or the strategies that could have been used to reduce both patient and staff doses. Almost all of the severe injuries that have occurred were avoidable.

Analysis of variations in contrast detail experiments

Three sources of variability in a contrast-detail (CD) experiment have been quantitated: within-observer variance, between-observer variance, and sample variance. It is concluded that (1) it is more efficient to increase the numbers of replicated images and observers than to increase the number of readings; (2) sampling and between-observer variations are approximately equal; (3) one can expect approximately 10% standard errors in the measured value of threshold detail or threshold contrast in a CD experiment which employs four observers, four replicate image samples, and one reading per observer.

Characteristics of radiation detectors for diagnostic radiology

The use of X-rays for diagnosis has been significant since its discovery. A measurement of the X-ray dose is the main determinant for risk vs benefit of these examinations. Radiation detectors are important for dose measurement. A description of these detectors, including the most frequently used ionization chamber, aids in the understanding necessary for their use. Proper and accurate use of detectors depends on an understanding of their calibration and their characteristics. Detectors such as ionization chamber, including specialized chambers, and solid detectors, including luminescent detectors, are described. This is followed by a description of the calibration process. The precision of measurements can be greatly affected by an understanding of the detector in use.