R 333.5688 Annual medical physicist’s quality control tests.

Rule 688. Before the radiation machine is used on patients and at least annually thereafter, a stereotactic breast biopsy facility shall have the medical physicist perform all of the following quality control tests: (a) Collimation assessment that meets either of the following: (i) For screen-film systems, the x-ray field shall be contained within the image receptor on all 3 sides except the chest wall edge. The x-ray field shall not extend beyond the chest wall edge of the image receptor by more than 2% of the source-image receptor distance. (ii) For digital image receptors, the x-ray field may extend beyond the edge of the image receptor on all 4 sides, but no edge of the x-ray field shall extend beyond the image receptor by more than 5 millimeters on any side. Distances shall be measured in, or referred to, the plane of the digital image receptor. (b) Focal spot performance and system limiting spatial resolution. Assess consistency of system-limiting resolution over time and in comparison to acceptance testing results using a line pair test pattern. (c) Peak tube potential (kVp) accuracy and reproducibility. The tube potential shall be accurate to within 5% of the indicated or selected potential. The coefficient of variation of reproducibility of the potential shall be less than or equal to 0.02 at the most commonly used clinical settings. (d) Beam quality assessment. The half-value layer shall be greater than or equal to the value kVp/100 in units of millimeter of aluminum. (e) Automatic exposure control system or manual exposure performance assessment that meets either of the following: (i) For screen-film systems, the image optical density shall be within 0.15 of the mean optical density when thicknesses of a homogeneous material is varied over a range of 4 to 8 centimeters using the clinical techniques for each thickness. If the optical densities do not meet this criterion, the medical physicist shall develop a technique chart which meets this criterion. (ii) For digital systems, the signal value at the center of the digital field of view shall remain within 20% of the signal obtained for the 4 centimeter phantom when thicknesses of a homogeneous material is varied over a range of 4 to 8 centimeters using the clinical techniques for each thickness. If the signal values do not meet this criterion, the medical physicist shall develop a technique chart which meets this criterion. (f) Image receptor speed uniformity that meets 1 of the following: (i) For screen-film systems, the difference between the maximum and minimum optical densities of all the cassettes in the facility shall not exceed 0.30. (ii) For digital systems, the signal-to-noise ratios (SNR) measured in each corner of the image shall be within 15% of the SNR measured at the center of the field of view. (iii) For digital systems that are not equipped with region of interest signal measurements, the machine shall meet the receptor uniformity requirements specified by the manufacturer. (g) Breast entrance exposure, average glandular dose, and exposure reproducibility. The coefficient of variation for both air kerma and current-time product (mAs) shall not exceed 0.05. The average glandular dose delivered during a single exposure of a department-approved phantom simulating a standard breast shall not exceed 3.0 milligrays (300 millirads) per exposure. The dose shall be determined with technique factors and conditions used clinically for a standard breast. (h) Image quality evaluation. An image of a department-approved phantom shall achieve at least the minimum score established in R 333.5689. (i) Artifact evaluation. System artifacts shall be evaluated with a high-grade, defect- free sheet of homogeneous material large enough to cover the full area of the exposed image receptor on the breast support assembly. (j) Localization accuracy test. Using a phantom made of gelatin or similar material, the biopsy needle shall capture the intended object in the phantom.