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Background: A Japanese multi-institutional prospective study was initiated to investigate the effectiveness and safety of accelerated partial breast irradiation (APBI) using strut-adjusted volume implant (SAVI) brachytherapy, with subjects registered between 2016 and 2021. Herein, we report the preliminary results on the feasibility of this treatment modality in Japan, focusing on the registration process, dosimetry, and acute toxicities., Patients and Methods: Primary registration was conducted before breast-conserving surgery (BCS) and the eligibility criteria included the following: age ≥ 40 years, tumor unifocal and unicentric, ≤ 3 cm in diameter, cN0M0, proven ductal, mucinous, tubular, medullary, or lobular carcinoma by needle biopsy. Secondary registration was conducted after BCS had been performed leaving a cavity for device implantation and pathological evaluations, and the eligibility criteria were as follows: negative surgical margin, tumor ≤ 3 cm in diameter on gross pathological examination, histologically confirmed ductal, mucinous, tubular medullary, colloid, or lobular carcinoma, pN0, L0V0, no extensive ductal component, no initiation of chemotherapy within 2 weeks of the brachytherapy APBI planning with SAVI was performed for the patients successfully entered in the study by the secondary registration process, and the treatment was administered at the dose of 34 Gy in 10 fractions administered twice daily., Results: Between 2016 and 2021, 64 women were enrolled in the study through primary registration, of which 19 were excluded from the secondary registration process, and in one, it was deemed impossible to comply with the dose constraints established during treatment planning. After the exclusion of these latter 20 patients, we treated the remaining 44 patients by APBI with SAVI. The dose constraints could be adhered to in all the patients, but re-planning was necessitated in 3 patients because of applicator movement during the treatment period. Grade 2 acute toxicities were observed in 18% of all patients, but more severe acute toxicities than Grade 2 were not observed in any of the patients., Conclusion: APBI with SAVI brachytherapy is feasible in Japan from the aspects of compliance with dose constraints and frequency of acute toxicities., (© 2023. The Author(s), under exclusive licence to The Japanese Breast Cancer Society.)

In Japan, cylindrical excisions are commonly performed in partial mastectomies for breast-conserving therapy, as opposed to the typical lumpectomies. Hence, when implementing Accelerated Partial Breast Irradiation (APBI) with the use of SAVI, a multi-lumen single catheter for partial breast irradiation with brachytherapy, discrepancies were noted between the shape of the excision cavity and the SAVI. Our institution reexamined the correlation between the form of the excision cavity and the shape of SAVI in instances of APBI that utilized post-operative SAVI insertion. To reconcile the discrepancy between the surgical cavity and the shape of the SAVI, we devised a hybrid APBI incorporating a supplementary catheter into the surrounding region of the SAVI and validated the dose distribution through simulation with a restricted quantity of supplementary catheters. Utilizing the obtained results, we present the outcomes of the hybrid APBI in actual clinical application. The objective of this investigation was to examine and augment the congruity between the SAVI applicator and the residual excision cavity following partial mastectomy in cases of APBI with SAVI in Japan. Our evaluation encompasses four instances of APBI with postoperative insertion of SAVI, conducted at our institution between December 2018 and May 2019. The affected breasts included three right and one left, with two cases each affecting regions C and D. Through a postoperative insertion approach, each case was strategically placed from the inframammary fold. The treatment plan was executed using Oncentra brachy (Electa), with a prescribed dose of 34 Gy/10 Fr delivered through IPSA for PTV_EVAL. Our review of the outcomes prompted the implementation of hybrid APBI in three patients from the year 2020. The mean volume of the PTV_EVAL was observed to be 75.71 mL in the four cases of Accelerated Partial Breast Irradiation (APBI) with postoperative insertion of the SAVI applicator evaluated in this study. Out of these, three cases demonstrated a deviation of more than 10% in volume between the SAVI applicator and AIR, resulting in suboptimal dose delivery to the target volume (PTV_EVAL), which was evidenced by D90 failing to reach 90% in each case. Upon further analysis, the discrepancy was found to arise from the irregular shape of AIR on the chest wall side or bilaterally on the CT cross-section perpendicular to the SAVI, which had taken on a dog-ear form. To address this issue, a virtual hybrid APBI approach was implemented by adding one or two catheters placed along the SAVI applicator, leading to a substantial improvement in the D90 of PTV_EVAL in all three cases, reaching 90% in each. Based on this result, the hybrid approach was executed by inserting intra-tissue catheters near the prominent AIR, parallel to the SAVI applicator, under ultrasound guidance. The average D90 delivered by the SAVI alone was 74.39%, which improved to 95.90% with the addition of the intra-tissue catheter, thereby demonstrating the efficacy of the hybrid APBI approach in enhancing the compatibility between the residual excision cavity and the SAVI applicator following partial mastectomy. The conformation of the SAVI applicator may not align with the partial mastectomy cavity in Japan. The addition of a small number of intra-tissue catheters improves how well the SAVI method works and makes the treatment more effective. [ABSTRACT FROM AUTHOR]

Purpose: We conducted a multi-institutional prospective study on accelerated partial breast irradiation (APBI) using interstitial brachytherapy. The clinical results over a minimum follow-up period of 30 months are presented here.Materials and Methods: Forty-six patients with breast cancer were treated with breast-conserving surgery and postoperative APBI. After confirmation of negative surgical margins and negative lymph nodes, a high-dose-rate brachytherapy protocol of 36 Gy/6 fractions was carried out. All clinical data were prospectively collected using the Common Terminology Criteria for Adverse Events ver. 3.0.Results: No recurrence was observed. Cumulative rates of grade 2 or higher late sequelae were 25% for fibrosis, 2% for fractures, 9% for pain, and 9% for soft tissue necrosis. Rates of excellent or good cosmetic results as assessed by the physician and patient were 93 and 89% at the 12-month follow-up and 76 and 74% at the 30-month follow-up, respectively. Large volumes of resected tissue in small breasts were associated with fibrosis of grade 2 or higher.Conclusion: APBI in Japanese women provides satisfactory clinical results except for cosmetic outcomes. There is some difficulty with the assessment of fibrosis and cosmetic outcomes, especially in patients with small breasts.Clinical Trial Registration Number: UMIN000001677. [ABSTRACT FROM AUTHOR]

Background: We carried out the first multi-institutional prospective study on accelerated partial breast irradiation (APBI) via multicatheter interstitial brachytherapy in a shorter period for early breast cancer in Japan., Methods: Patient eligibility criteria included positive hormone receptors, tumors ≤ 3 cm and TNM stage pN0M0. After breast-conserving surgery (Japanese cylindrical resection) and histological confirmation of negative surgical margins and the absence of lymph node metastasis, applicator implantation was performed either postoperatively or intraoperatively. High-dose-rate brachytherapy of 36 Gy in 6 fractions was delivered., Results: Forty-six patients from six institutions received this treatment regimen, and the median follow-up time was 60 months (range 57-67 months). The median resected breast tissue volume was 81 cm 3 (range 28-260 cm 3 ). No Grade 4 late sequela, local recurrence nor death due to breast cancer were observed. Grade 2-3 sequelae such as rib fracture (2%), soft tissue necrosis (9%), fibrosis (20%), and breast pain (9%) were observed. The resected breast tissue volumes of the patients who had Grade ≥ 2 fibrosis and Grade < 2 fibrosis were 105.9 ± 32.3 cm 3 and 76.3 ± 45.6 cm 3 , respectively, p = 0.02. The overall cosmetic outcome score of Excellent/Good was 74% at 60 months after APBI. Grade ≥ 1 fibrosis was observed in 44% and 92% of patients who scored Excellent/Good and Fair/Poor, respectively, p = 0.004., Conclusions: This study showed excellent local control and survival results with minimal late sequelae., (© 2022. The Author(s), under exclusive licence to The Japanese Breast Cancer Society.)