TH-AB-201-10: A New Technique for Fluoroscopic Radiation Field Size Confirmation

Abstract

Purpose: The confirmation of congruence between the radiation field and displayed image is an important part of routine fluoroscopic quality assurance testing. However, this test can be challenging, inaccurate, wasteful, or involve unnecessary staff exposure. This work describes a simple, accurate, inexpensive, and safe technique to complete this measurement. Methods: This technique relies on two easily-constructed custom components: (1) radiochromic film strips made from blank film sheets and a laser printer, and (2) a lead blocker fabricated from lead sheets and a CR-type cassette housing. A standard collimation test tool is positioned near the fluoroscopic image receptor and imaged with an open collimator. Based on this image, small radiochromic film strips are positioned on the collimation tool at the edges of displayed image. Without moving the collimation tool or film strips, the 1/8-inch lead blocker is slid in between the collimation tool and image receptor. The blocker protects the image receptor and simultaneously drives the system to maximum output, which rapidly darkens the radiochromic film strips. The deviation between the radiation field and displayed image is recorded using the millimeter scale printed on directly on the film strips. Results: The efficacy of this technique was demonstrated on over 50 fluoroscopy systems in the Henry Ford Health System (including both fixed and mobile C-arms, classic R&F rooms, and both image intensifier and flat panel detector systems). The test was performed with the operator in control room or behind mobile radiation shield. The total cost of disposable materials for each test was less than $1. Accuracy within 1–2 mm was achieved for each edge of the radiation field. Conclusion: An accurate, economical, and safe technique was successfully implemented to measure the congruence of the radiation field and displayed image in fluoroscopy systems.