PO123

Purpose 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. Materials and Methods 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. Results 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. Conclusions 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. 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.