Five day accelerated partial breast irradiation (APBI) using stereotactic body radiation therapy (SBRT) in stage 0-II breast cancer: A report of 135 cases with up to two-year follow-up.

e12596 Background: Randomized trials in stage 0-II breast cancer have proven that APBI given via HDR implant in 5 days is equivalent to whole breast External Radiation Therapy (XRT) given in 5-6 weeks in regard to breast tumor local recurrence (LR). However, complications have been significant. Recently APBI using non-invasive IMRT given in 5 fractions has been shown in another randomized trial to be equivalent to XRT in 6 weeks, with respect to LR. IMRT was superior in regard to acute effects, late effects, and cosmesis. In the randomized clinical trial of APBI IMRT, the Clinical Target Volume (CTV) was defined by the injection of individual fiducial markers bordering the surgical cavity. At our institution, we have used the Biozorb fiducial system to localize the CTV for IMRT. We sought to confirm the APBI IMRT results with this simpler less labor intensive fiducial placement system. Methods: Between 2017 and 2020, 135 patients have undergone SBRT targeted to a Biozorb defined CTV with the walls of the surgical cavity sewn to the Biozorb device. Eligible patients were older than age 40, had tumor sizes < 3 cm, negative surgical margins, and negative sentinel node dissections. SBRT dose was 30 Gy given in 5 fractions. Dose Constraints were as follows: V-30 Gy < 105%, Ipsilateral Breast V-15 Gy < 50%, Ipsilateral Lung V-10 Gy < 20%, Contralateral Lung V-5 Gy < 10%, Heart V-3 Gy < 20%, Contralateral Breast Dmax < 2 Gy and Skin Dmax < 27 Gy. The Planning Target Volume (PTV) ranged from 27 to 355 cc with a median of 80 cc. PTV = CTV + 1-2 cm. Results: Follow-up ranged from 1-26 months with a median of 12 months. LR has been 0% (0/135). There have been no skin reactions or seromas. Infection has occurred in one patient (0.7%). Three (2.2%) patients developed pain around the Biozorb site. This resolved within 2 days on a short course of steroids in all cases. Cosmetic results as rated by the Surgeon, Radiation Oncologist, and Nurse, were rated excellent in 98.5% (133/135) of cases. Conclusions: Non-invasive APBI with SBRT given qd over 5 days targeted to Biozorb has resulted in LR, complications, and cosmetic results which compare favorably to invasive APBI given bid with HDR implant. At last follow-up, there have been no LR, skin reactions, or significant complications. Cosmesis has been excellent in 98.5% of patients.