Advantages of upright position imaging with medium-energy collimator for sentinel node lymphoscintigraphy in breast cancer patients

Abstract

Objective: To evaluate the advantage of upright position imaging with a medium-energy collimator for the detection of sentinel lymph node (SLN). Methods: Thirty-four patients with operable breast cancer underwent sentinel node lymphoscintigraphy with 99m Tc-tin colloid. Images were obtained in 5 different positions and paired images from the same patient were compared using side-by-side interpretation. Images were compared in 3 groups: group 1 (anterior view); supine (SAV) vs. upright (UAV), group 2 (oblique view); supine (SOV) vs. upright (UOV), and group 3 (oblique view); modified supine (MOV) vs. UOV. Image quality was evaluated using a 3-grade scale of clear, faint, and equivocal depiction, and correlated to 3 parameters: distance from injection site to lymph node (hot node), counts in hot node, and image contrast. Parameters in group 1 were compared by classifying the primary tumor site into 4 subregions. Results: Image quality in all 3 groups was more enhanced on the image obtained in the upright position than that in the supine position. Obtaining images in an upright position increased the mean distances by 1.5-3.2 cm, and mean contrasts were significantly increased by 0.13-0.31 (p < 0.05). It was shown that image quality was more greatly affected by image contrast than by counts in the hot node. Image contrast of 0.5 seemed an appropriate threshold level for detection of the hot node. On comparison of tumor sites, the upper outer quadrant (C) region of the 4 subregions demonstrated greater contrast enhancement on upright position images. Conclusion: Clinical images obtained in an upright position with a mediumenergy collimator were superior to those obtained in a supine position. Use of this procedure is recommended to enhance lymph node detection on sentinel node lymphoscintigraphy.

Evaluation of the subtraction method utilizing posterior view for improving visibility of the sentinel lymph nodes for lymphoscintigraphy in breast cancer

“…Tsushima et al [16] reported the appearance of star-shaped artifacts caused by septal γ-ray penetration, which could impair the visualization of SLNs located near the tumor. Based on this report, the routine imaging in authorial institution is using a LEGP with a thick septal to suppress the appearance of artifacts.…”

“…For example, several papers [8][9][10][11][12] reported that modifying the imaging position improved the accuracy of SLN detection. As these methods increased the distance between the C region and axilla by modifying the imaging position, scattering from the injection site could be avoided.…”

“…As these methods increased the distance between the C region and axilla by modifying the imaging position, scattering from the injection site could be avoided. In addition, other methods, including incorporation of a lead shield [7], changes in the acquisition energy window [18], and collimators [14][15][16], were reported in several papers. These methods were performed with the intent to directly reduce scattering at the injection site.…”

“…To address this disadvantage, multiple methods [7][8][9][10][11][12][13][14][15][16][17][18] have been developed to minimize the effects of scattering and to improve SLN visibility during lymphoscintigraphy imaging. However, the use of these methods requires a new imaging in addition to as the usual imaging.…”

The sentinel node in breast cancer

“…SPECT CT improves pre-operative localisation of draining nodes by detecting nodes missed by planar imaging, excluding non-nodal false positive sites of uptake and accurately localising axillary and extra-axillary nodes particularly in those who are overweight [55,56] . Upright imaging may also be advantageous [57] . Recent work has also shown the potential of the portable gamma camera in theatre over the hand-held probe [58] .…”