When Is CT-Based Postoperative Seroma Most Useful to Plan Partial Breast Radiotherapy? Evaluation of Clinical Factors Affecting Seroma Volume and Clarity

Purpose: To evaluate the effect of the time from surgery and other clinical factors on seroma volume and clarity and establish the optimal time to use the computed tomography (CT)-based seroma to plan partial breast irradiation (PBI). Methods and Materials: A total of 205 women with early-stage breast cancer underwent planning CT after breast-conserving surgery. One radiation oncologist contoured the seroma volume and scored the seroma clarity, using a standardized Seroma Clarity Score scale, from 0 (not detectable) to 5 (clearest). Univariate and multivariate analyses were performed to evaluate the associations between the seroma characteristics and the interval from surgery and other clinical factors. Results: The mean interval from surgery to CT was 84 days (standard deviation 59). During postoperative Weeks 3–8, the mean seroma volume decreased from 47 to 30 cm3, stabilized during Weeks 9–14 (mean 21) and was involuted beyond 14 weeks (mean 9 cm3). The mean seroma clarity score was 3.4 at Weeks 3–8, 2.5 at Weeks 9–14, and 1.6 after 14 weeks. The seroma clarity was greater in patients aged ≥70 years. The seroma volume and clarity correlated significantly with the volume of excised breast tissue but not with the maximal tumor diameter, surgical re-excision, or chemotherapy use. Conclusion: The optimal time to obtain the planning CT scan for PBI is within 8 weeks after surgery. During Weeks 9–14, the seroma might remain adequately defined in some patients; however, after 14 weeks, alternate strategies are needed to identify the PBI target. The lack of correlation between the seroma volume and tumor size suggests that the CT-based seroma should not be the sole guide for PBI target volume definition. [Copyright &y& Elsevier]