Abstract P3-12-09: Dosimetric analysis of the pattern of local recurrence in breast cancer patients undergoing breast reconstruction and post-mastectomy radiotherapy

Background This study aims to identify spatial and dosimetric patterns of breast cancer relapse in a mono-institutional large series of patients treated with mastectomy and various forms of breast reconstruction. Material and Methods We retrospectively reviewed 196 patients with Stage II-III breast cancer treated with modified radical mastectomy between 1995 and 2016 at the Radiotherapy Department of Careggi Hospital, Florence. All patients performed Skin-sparing mastectomy or nipple-sparing mastectomy with immediate or delayed breast reconstruction and subsequently received post-mastectomy radiotherapy (PMRT). Systemic therapy was prescribed as per local and international guidelines both in neoadjuvant and adjuvant setting. All patients were treated with 3DCRT technique. Diagnostic imaging (e.g. CT, MRI) obtained at recurrence were registered with the original planning computed tomography (pCT) for the dosimetric analysis. Recurrence gross tumor volume (rGTV) were delineated and co-registered with pCT. All rGTV were compared dosimetrically to planned dose and spatially with planning target volumes. Locoregional recurrence (LR) were divided in three categories relative to the high dose region, 95% of prescription dose (D95%). We defined “in field LR” those with more than 90% of their volume within D95% region,“marginal LR” when recurrence volume was between 20 and 90% within D95% and “outfield LR” those with less than 20% of their volume D95%. Results The median age was 49 years (range, 26 - 83 years).163 women (83 %) were classified as stage III; 118 women (60 %) had more than three positive axillary nodes. The majority of lesions were estrogen receptor positive ( 75 %), grade 3 (52%) ,with the presence of LVI (60 %). Adjuvant RT at chest wall were performed in all patients, most of whom underwent a RT of chest wall +infra- supraclavicular nodes (71%).Prescribed RT dose was 50 Gy in 25 fractions. With a median follow-up of 60 months (range, 12-240 months), 22 (11%) patients experienced a locoregional relapse: 10 patients in the chest wall; 7 in ipsilateral axillary region +/- chest wall; 3 in internal mammary nodes -/+ chest wall; one locoregional relapse was observed in the supraclavicular nodes. Most of relapses were G3 (75%) with documented LVI (79%). The topographic analysis of the local failure patterns showed: thirteen (59 %) were “in-field LR”; 9 (41%) were “out-field LR” . For the spatial analysis, all relapses on the chest wall were observed above the breast tissue expander or mammary prosthesis. Free time from recurrence disease was 30 months (range 5-86 months). Conclusion This study suggests that chest wall recurrences are rare after PMRT and are related to biologic aggressiveness of the disease than to inadequate irradiation of target volumes. Prospective studies are warranted to evaluate the relationship between treatment volumes and patterns of recurrences in order to refine new delineation guidelines for women undergoing PMRT and breast reconstruction. Citation Format: Desideri I, Meattini I, Becherini C, Francolini G, Scotti V, Olmetto E, Perna M, Topulli J, Livi L. Dosimetric analysis of the pattern of local recurrence in breast cancer patients undergoing breast reconstruction and post-mastectomy radiotherapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-12-09.