IABR plays a vital role for breast cancer patients in terms of preserving anatomical landmarks, minimizing scar fibrosis, reducing the total number of operations, and improving patient satisfaction and psychological outcomes. This is primarily because the long-term success and aesthetic satisfaction of autologous reconstruction are superior to delayed or alloplastic reconstruction [19-21]. However, there are scant data on the effect of RT on autologous flaps. In this cohort study, we focused on assessing the efficacy and safety of IABR with or without RT. The results showed that subsequent RT was well tolerated by patients who received IABR after BCS, and that patients were satisfied with the aesthetic outcomes, suggesting that RT had no serious effects on autologous tissue flaps.
Recently, autologous grafting has become much more widely used in breast cancer patients who need breast reconstruction because of its improved oncological outcomes and reconstruction quality [22, 23]. Additionally, surgeons are increasingly inclined to perform immediate breast reconstruction for patients who need adjuvant RT . Studies have shown significantly improved aesthetic outcomes of grafted autologous flaps after mastectomy [25, 26]. However, aesthetic outcomes of RT following IABR have been contradictory . Several previous studies [28-30], which included a total of 96 patients, evaluated aesthetic outcomes of reconstructed breasts after mastectomy by quartile scores based on patients’ self-evaluation; roughly 77.1% of the cases reported very good or good outcomes after RT. In our study, the rate of aesthetic outcomes being considered very good or good was the lowest for the RT group (62.5%) at 1 month after RT (T1) but reached 96.9% at 6 months after RT (T6), which was higher than previously reports. The differences might be caused by different radiation technique, methods of breast tumor resection, and/or breast reconstruction. In our study, 90.6% (29/32) of patients in the RT group underwent intensity modulated RT (IMRT) rather than 2- or 3-dimensional conformal RT for whole breast irradiation. IMRT could improve the dose distribution of treatment fields in the breast; thus, it might result in superior breast cosmesis and less palpable induration . Additionally, all patients in our study retained partial breast tissue and needed a small transfer flap rather than replacement of the whole breast tissue with a flap, which provided restoration with a natural texture, shape, and volume of the breast.
Although a few studies have reported data of aesthetic results after RT for patients who received IABR after BCS, aesthetic evaluations at different timepoints after RT and a comparative analysis between aesthetic results for patients with and without RT are still lacking. One early study  that included 34 patients who underwent RT at 4 to 6 weeks after IABR reported that the proportion of very good or good cosmetic outcomes was only 88.2%, which was lower than that of our study (96.9%). This difference might be due to the higher proportion of unaesthetic scars (8.9%) and marked fibrosis (2.9%) caused by the surgical methods used in that study. Unlike that study, we used LD flaps or FDFG to fill the defect through the primary incision so that an additional incision was avoided. Additionally, heterogeneity in the timepoints at which aesthetic outcomes were evaluated may be another reason. In our study, we evaluated cosmetic outcomes at different timepoints before and after radiotherapy and IABR. Additionally, the cosmetic outcomes of patients in the non-RT group were evaluated at the same timepoints. Thus, we observed that compared with the non-RT group, the addition of radiotherapy in the RT group did not affect cosmetic outcomes, indicating that RT might be a feasible option for breast cancer patients undergoing IABR after BCS because of durable cosmetic outcomes.
Postoperative flap volume changes are usually used to assess how much of the flap volume will ultimately remain. There is still a paucity of literature on flap volume changes following autologous flap breast reconstruction. Kimura et al.  described a maximum decrease in fat volume of 75.1% at 1 year after the operation, while Wilting et al.  showed a final overall flap volume decrease of 88.9% after 6 months. Rochlin et al.  found the incidence rate of flap volume loss events to be 16.9% among patients who received radiotherapy following IABR after mastectomy, but data on the impact of RT on flap volume changes are lacking. In this study, we assessed the changes of flap size in the three dimensions instead of volume changes, and our findings indicated that the size of the flap decreased slowly and tended to stabilize at the T1, T6, and T12 timepoints regardless of RT. Thus, RT had no adverse effect on flap size compared with the non-RT group. It is noteworthy that the flap size decreased obviously at an average of 4 months, which was shorter than what has been reported in previous studies [33, 34]. This may be related to the relatively smaller flap size required for BCS than for mastectomy, differences in patient populations or flap donor sites, baseline measurement times, measurement techniques used to evaluate flap size, and host conditions. Currently, there are no reports on the factors that affect the initial flap size after autologous reconstruction, but the reduction in flap size may be partially due to early postoperative factors such as apoptosis , postoperative edema, and inflammation. Flap denervation and ischemic changes caused by transient ischemia may also contribute to this reduction.
In our study, the common postoperative complications were partial necrosis of the flap, infection, hematoma, and seroma, the incidence rates of which were between 1.2% and 3.6%, which were lower than the 2.9% to 14.7% reported in previous studies [10, 17, 23, 36]. Different patient populations, excision extensions, flap sizes, and donor sites might lead to this difference. Patients from Western countries or who undergo mastectomy usually need larger flaps and more quantity of fat grafting to balance the esthetic and oncological aspects of the larger breast size, which can easily lead to impaired blood supply in the grafting site. In contrast, due to the small- to medium-sized breasts in the Asian population, all patients in our study underwent BCS followed by IABR with smaller flaps, which can avoid the local unsatisfactory blood supply. Additionally, most of the patients (57/84) in our study underwent IABR with LD flaps, so few patients experienced the risk of fat necrosis or liquefaction, which was commonly seen in the above studies. Nevertheless, there is still controversy regarding whether RT could increase the risk of postoperative complications . By summarizing the data of 11 retrospective studies that included 316 patients who received RT following IABR after mastectomy, Rochlin et al.  concluded that postoperative complications of fat necrosis and contracture could be increased to 16.9% and 35.4%, respectively, by RT. However, our study showed that RT did not increase the risk of any postoperative complications for patients who underwent IABR following BCS when compare with the non-RT group. No patients experienced contracture or fat necrosis in either group, and only one patient in the RT group (1.2%) experienced partial necrosis. This is likely because the scope of surgical resection in our study was smaller than that of mastectomy, and retained some neurovascular function, which relatively reduced RT-related complications.
In this cohort study, patients who received IABR and RT did not experience any grade ≥3 RT-associated AEs. Notably, compared with no radiation dermatitis cases among patients who only received whole breast irradiation, 12 patients (37.5%) with boost irradiation to the tumor bed experienced grade 1 radiation dermatitis during RT, but the dermatitis gradually disappeared after radiotherapy. A previous report  showed that the tumor bed could be markedly replaced with flaps during reconstruction following BCS. Although tumor bed boosted radiotherapy following whole breast irradiation can reduce local recurrence rates, researchers have found no evidence of a benefit for other oncological outcomes among BCS patients . In light of this, it is necessary to conduct multidisciplinary discussions with breast surgeons, oncologist, and radiotherapists to accurately determine the location of the tumor bed and decide whether to perform tumor bed boosting during radiotherapy.
The introduction of oncoplastic techniques into clinical practice has the potential to reduce the risk of positive margins and ultimately the risk of local recurrence . In our study, to ensure negative margins, we often performed a safer edge in the range of 1.5–3 cm, which is between the traditional BCS and mastectomy. RT was conducted in 38.1% of patients due to large tumors, lymph node metastases, or other high-risk factors. At a median follow-up of 33.3 months, all 84 analyzable patients remain alive, and median disease-free survival time has not been reached. In total, 3.57% of patients had regional recurrences (3.13% in the RT group and 3.85% in the non-RT group). No patient experienced local recurrence in the subsequent 33.3 months of follow-up. This benefit for patients who underwent IABR may come from both RT and safer surgical margins.
However, there are also some limitations to this study. The inherent limitations of the study are its small sample size and retrospective nature. Additionally, the follow-up time is insufficient to definitively evaluate long-term outcomes. Some RT-associated late complications like fibrosis need further follow-up.