SPECT/CT dramatically cuts radiation dose in some breast cancer patients

Dose reduction at one time played second fiddle to image quality, but today it enjoys top billing. New algorithms are coming into play in CT, radiography, and fluoroscopy to maintain image quality at traditional levels by processing out the noise that sneaks in during low-dose exams. In some cases, fear of radiation has gotten so bad that patients forego CT and other sources of ionizing radiation all together.

But now the source of radiation fear may, at least in some cases, be the means for dramatically reducing it. Dr. Andrea Cheville, a consultant in physical medicine and rehabilitation, and colleagues at the Mayo Clinic in Rochester, MN, contend that SPECT/CT can actually reduce the net radiation dose for breast cancer patients.

The Mayo researchers used SPECT/CT to exactly identify and localize critical lymph nodes in the underarm area of 30 women with early-stage, low-risk breast cancer. In so doing, they were able to create individualized treatment plans that protected these patients against lymphedema, a swelling of tissue that occurs from radiation-induced damage.

“We took these SPECT/CT images and fused them with the CT images from radiation planning and were able to individually tailor-essentially personalize-the (treatment) fields for each of these women such that the tumor and tumor beds received adequate doses of radiation while the lymph nodes that drain the arm were maximally spared,” she said.

Cheville notes that there may be as many as 62 lymph nodes under the arm. But only a few perform the critically important function of draining fluid. SPECT/CT pinpointed the exact location of these nodes, 65% of which would have been located within the standard radiation treatment area. Identifying these nodes allowed the Mayo team to take steps to shield them from the radiation applied during treatment.

Not all critically important nodes could be completely shielded. But among the 25 patients with at least one critical lymph node within the radiation treatment field, at least some shielding was possible in each case. Cheville and colleagues estimate that the individualized plans and shielding reduced from 26% to 4% the number of lymph nodes that received a moderate dose of radiation.

The 30 subjects, who were participating in an ongoing prospective cohort study, had tumors surgically removed. Each was scheduled for radiotherapy to the affected breast. Either their lymph nodes tested negative for metastatic spread or had only micrometastasis. As a result, radiation to the lymph nodes in the armpit was not warranted in these patients.

Two treatment plans, a standard one and an individualized plan based on SPECT/CT data, were completed for each patient. These tailored plans were designed to spare lymph nodes, especially critical ones, from as much radiation as possible

Cheville estimates that if these patients’ lymph nodes had not been shielded from the radiation, their risk of developing lymphedema may have been as high as 50%. No cases of lymphedema have yet been reported in the cohort. But because lymphedema can take years to develop, the researchers are continuing to monitor the subjects.

“Sometimes that starts two, three, or five years after the radiation, so it’s a little harder to study,” she said. “But we can infer from (previous research) that if we are able to reduce the radiation that we deliver to critical nodes, we should reduce not only the risk of lymphedema, but also the risk of progressive and severe lymphedema.”