Impact of Varying Chest Wall Target Volume Delineation on Postmastectomy Radiation Therapy Outcomes in Breast Cancer Patients with Implant-Based Reconstruction

Background: The target volume for post-mastectomy radiation therapy (PMRT) in breast cancer patients with reconstruction has been a subject of debate. Traditionally, the RT chest wall (CW) volume encompasses the entire implant. For patients with retropectoral implants, the deep lymphatic plexus dorsal part of the implant is no longer considered high risk and can be omitted. This study aimed to assess the radiation dose distribution and treatment outcomes associated with different CW delineation according to ESTRO ACROP guideline for patients who have undergone implant-based reconstruction. Methods: We conducted a retrospective review of breast cancer patients who underwent a mastectomy followed by two-stage implant-based breast reconstruction and adjuvant radiation therapy (RT) between 2007 and 2022. The expanders/implants were positioned retropectorally. The chest wall target volumes were categorized into two groups: the prepectoral group, which excluded the deep lymphatic plexus, and the whole expander group. Results: The study included 26 patients, with 15 in the prepectoral group and 11 in the whole expander group. No significant differences were observed in normal organ exposure between the two groups. There was a trend toward a lower ipsilateral lung mean dose in the prepectoral group (10.2 vs. 11.1 Gy, p = 0.06). Both groups exhibited limited instances of reconstruction failure and local recurrence. Conclusions: For patients undergoing two-stage expander/implant retropectoral breast reconstruction and PMRT, our data provided comparable outcomes and normal organ exposure for those omitting the deep lymphatic plexus.