Patient-specific treatment plans devised using images from a combination of single photon emission computed tomography (SPECT) and computed tomography (CT) may reduce radiation-induced lymph node damage without sacrificing treatment outcomes, according to a small study released at the San Antonio Breast Cancer Symposium this past weekend.
Because lymphedema is a common complication of breast cancer treatment, Cheville and colleagues sought a method to create individualized postsurgical irradiation plans that would spare as many axillary and supraclavicular lymph nodes as possible. First, for each of 22 patients the researchers identified the location of small, nonpathological but physiologically relevant lymph nodes (those which drain the arm after breast cancer surgery) by administering filtered 99mTc sulfur colloid followed by SPECT/CT scan. The patients had with early-stage low-risk breast cancer with no known positive lymph nodes or only micrometastasis to the lymph nodes.
The SPECT/CT images were loaded into the radiation planning software and the software instructed to contour the draining nodes to receive a maximum of 50% intensity, although, as the researchers noted, the maximum radiation threshold to preserve physiologic integrity is not yet known. The software also ensured that ≥50 Gy or biologic equivalent would be delivered to the target tissue.
The researchers then compared these treatment plans with ones developed using standard clinical practice. In total, they identified 53 draining lymph nodes, 54% of which would be inside the treatment field if standard practice plans were used but could be blocked if the SPECT/CT plan was used. With the standard practice plan, 62% of nodes would receive ≥10 Gy and 27% would receive ≥40 Gy. With the SPECT/CT plans, only 17% would receive ≥10 Gy and 6% would receive ≥40 Gy.
The patients will be followed for the development of lymphedema, to help determine the exposure threshold below which physiologic integrity is preserved.