Abstract P4-11-20: Integration of SPECT/CT Lymphoscintigraphy into Breast Cancer Radiation for Lymphatic Sparing

Abstract Lymphedema (LE) is a common complication of cancer treatment, and has been identified as the number one issue by breast cancer survivors with incidence as high as 70%. Given the long-term survivorship of these women, LE is a widely prevalent condition. Irradiation of axillary and supraclavicular lymph nodes increases a patient's risk of LE onset and progression by as much as 2-fold. It is anticipated that a more individualized approach to post-surgical irradiation of breast cancer patients may reduce radiation-induced lymph node (LN) damage without sacrificing control rates, although it is noted that a definitive radiation exposure threshold below which LNs physiological integrity will be preserved is currently lacking. To identify the locations of the small, non-pathological but physiologically relevant LNs which drain the arm after breast cancer surgery and incorporate them into radiation planning, filtered 99mTc sulfur colloid (TcSC) was administered and a SPECT-CT scan was acquired for 22 patients immobilized in the treatment position. These images were registered with the Radiation Oncology planning CT scan, and draining LN were contoured automatically using a threshold of 50% maximum intensity. Two treatment plans were generated for each patient, one per routine clinical practice (STD) and the other (MOD) with treatment fields modified to minimize dose to the LNs visible on SPECT/CT images while ensuringthat ≥50Gy or biologic equivalent is delivered to target tissues. 53 draining LN were identified, 54% of which were inside the STD plan fields but could be blocked in the MOD plan fields. 62% of LN in the STD plans vs. 17% in the MOD plans receiving a mean of ≥10Gy, and 27% in the STD plans vs. 6% in the MOD plans receiving a mean of ≥40Gy. Patient-specific LN dose reduction can be achieved through integration of SPECT/CT images into the radiation planning process. These patients will be followed for the development of LE, to estimate an exposure threshold below which LN preservation is assured. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-11-20.</jats:p