Hypofractionated Whole-Breast-IMRT with HDR Brachytherapy Boost in Early-Stage Breast Cancer: Long Term Results of a Single Center Study

Abstract

<h3>Purpose/Objective(s)</h3> In breast cancer patients, the addition of a boost over the lumpectomy bed after whole breast radiotherapy is frequently included in the therapeutic protocol and interstitial brachytherapy (BT) is one of the options for its administration. When BT is performed after conventional fractionation (50Gy) is considered safe, effective and strongly supported by literature. However, few studies have described its efficacy and side effects after a hypofractionated scheme, and even fewer have reported treatment/patient-dependent factors that may influence toxicity. The aim of this study is to show our results from a group of patients treated under a hypofractionated forward-planned whole-breast IMRT (Hypo-WB-IMRT) scheme followed by a high-dose-rate brachytherapy boost (HDR-BT) after conservative surgery. <h3>Materials/Methods</h3> We evaluated all patients treated at our facility with Hypo-WB-IMRT without elective irradiation of lymphatic areas (40Gy/15sessions) with a sequential single application of HDR-BT of 7 to 12Gy. A breast MRI was performed in all patients at the time of diagnosis. The BT implant was designed using both diagnostic MRI and planning CT as a reference for tumor bed localization and was planned according to the modified Paris system, with rigid needles, local anesthesia and outpatient regimen. <h3>Results</h3> Between 2009 and 2017, 638 patients with early-stage invasive breast cancer or ductal carcinoma in situ received adjuvant treatment according to the aforementioned protocol after breast-conserving surgery. Median follow-up was 6 years (4-11ys). We did not identify any relationship between the volume in cubic centimeters of the isodoses of 90%, 100%, 120% and 150% of the prescribed dose with acute (bleeding, mastitis) or long-term toxicity (12-month fibrosis, pain, edema, hypochromia, telangiectasia) or with an increased likelihood of local relapse or a second primary tumor in the same breast. However, and despite the low incidence of side effects and their slightness, we did identify an impact of breast volume with an increased risk of radiodermatitis at the end of WBRT (p=0.019), post-treatment mastitis (p=0,023), tumor bed fibrosis after 12 months (p=0.002), chronic pain (p=0.018) and breast edema (p<0.001) in women with >1000cc breasts with respect to smaller volume breasts. 13 patients had an actual local relapse (2.21%), 14 had a 2^nd primary in the same breast (2.39%) and 14 were diagnosed with contralateral breast cancer (2.39%). 16 patients (2.73%) developed metastatic disease and the overall survival at 11 years was 85.5%. <h3>Conclusion</h3> Hypo-WB-IMRT followed by a single dose HDR-BT boost is well tolerated, with a low rate of side effects and excellent oncologic outcomes. However, it may be of interest to individualize the treatment protocol choice in large breasts women who may be at higher risk of toxicity.