Automatic Monitoring of Localized Skin Dose with Fluoroscopic and Interventional Procedures

This software tool locates and computes the intensity of radiation skin dose resulting from fluoroscopically guided interventional procedures. It is comprised of multiple modules. Using standardized body specific geometric values, a software module defines a set of male and female patients arbitarily positioned on a fluoroscopy table. Simulated X-ray angiographic (XA) equipment includes XRII and digital detectors with or without bi-plane configurations and left and right facing tables. Skin dose estimates are localized by computing the exposure to each 0.01 × 0.01 m² on the surface of a patient irradiated by the X-ray beam. Digital Imaging and Communications in Medicine (DICOM) Structured Report Dose data sent to a modular dosimetry database automatically extracts the 11 XA tags necessary for peak skin dose computation. Skin dose calculation software uses these tags (gantry angles, air kerma at the patient entrance reference point, etc.) and applies appropriate corrections of exposure and beam location based on each irradiation event (fluoroscopy and acquistions). A physicist screen records the initial validation of the accuracy, patient and equipment geometry, DICOM compliance, exposure output calibration, backscatter factor, and table and pad attenuation once per system. A technologist screen specifies patient positioning, patient height and weight, and physician user. Peak skin dose is computed and localized; additionally, fluoroscopy duration and kerma area product values are electronically recorded and sent to the XA database. This approach fully addresses current limitations in meeting accreditation criteria, eliminates the need for paper logs at a XA console, and provides a method where automated ALARA montoring is possible including email and pager alerts.

The authors of this paper appreciate the helpful and insightful comments of the reviewers.

Authors and Affiliations

1. School of Computing, Informatics and Decision Systems Engineering, Arizona State University, Tempe, AZ, 85281, USA

   Yasaman Khodadadegan, Muhong Zhang & Teresa Wu

2. Department of Radiology, Mayo Clinic Arizona, 13400 East Shea Blvd, Scottsdale, AZ, 85258, USA

   William Pavlicek, Robert G. Paden & Brian Chong

3. Department of Radiology, Mayo Clinic Rochester, 200 First St. SW, Rochester, MN, 55905, USA

   Beth A. Schueler & Steve G. Langer

4. Department of Cardiology, Mayo Clinic Rochester, 200 First St. SW, Rochester, MN, 55905, USA

   Kenneth A. Fetterly

Corresponding author

Correspondence to Muhong Zhang.

Appendix

A Point Calculation of Air Kerma to a 0.01 × 0.01 m² Radiated Region

The origin is the X-ray source, and the base of the solid angle (cone for XRII pyramid for digital detectors) occurs at the patient entrance reference point (PERP). For a square-shaped field, the irradiated area will (Figure 10) depict an arbitrary surface area of the virtual patient surrounded by a pyramid-shaped field of radiation. The base of the pyramid is at the PERP distance (modified to be the projected s). Step 1 determines the total surface area lying within the projected field. The PERP plane (base of the pyramid) passes through PERP. The goal is to locate the four triangular faces to delineate an irradiated area on the patient.

Inverted pyramid with base located at PERP. Each side of the pyramid intercepts the skin of the patient to parse those radiated sections of the skin.

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First, we find two orthogonal vectors at PERP area as follows,

where v ₁ and v ₂ are parallel to the edges of the square field.

We denote the length of the side of the radiated area at PERP with l. The calculation for the coordinates of the four corners of the area is:

With three points on each triangle face, we can construct the four faces of the pyramid such as \( Ax + By + Cz + D = 0 \), where A, B, C, D are coefficients. As an example, for the plane consisting of source, \( \left( {{x_{{c_1}}},{y_{{c_1}}},{z_{{c_1}}}} \right) \) and \( \left( {{x_{{c_4}}},{y_{{c_4}}},{z_{{c_4}}}} \right) \) coefficients of plane are as follows,

Coefficients of other planes can be computed accordingly.

A conically shaped field having a circular base (at PERP) has a similar approach (Figure 11).

Cone with circular base.

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The vector v ₃ from X-ray tube to PERP as in Figure 12 is

Checking a point whether it is inside the cone or not.

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Assume that (x, y, z) represents the coordinate of a point on the patient skin to be checked if it has been exposed or not. Figure 12 depicts the vector v ₄ and schematic of the feasibility method. The distance from this point to the source is computed as follows,

Here, \( \parallel \cdot {\parallel_2} \) means the l ₂ norm, that is, \( \parallel \left( {a,b,c} \right){\parallel_2} = \sqrt {{{a^2} + {b^2} + {c^2}}} . \)

The radius of the area at Patient Entrance Reference Point level;

For the two vectors, we have \( {v_3} \cdot {v_4} = \parallel {v_3}{\parallel_2} \times \parallel {v_4}{\parallel_2} \times {\hbox{ Cos}}\theta \), where θ is the angle between vector v ₃ and v ₄. Thus, any point on the patient skin, i.e., (x, y, z) satisfying

is inside the cone and would have been radiated.

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