Five Day Accelerated Partial Breast Irradiation (APBI) Using Stereotactic Body Radiation Therapy (SBRT) in Stage 0-II Breast Cancer: A Report of 218 Cases With Up to 39 Month Follow-Up

Randomized trials in selected early-stage breast cancer patients with up to 10-year follow-up have proven that Accelerated Partial Breast Irradiation (APBI) given via High Dose Rate (HDR) implant bid in 5 days is equivalent to whole breast irradiation (WBI) given q.d. in 5-6 weeks in regard to breast tumor local recurrence (LR). However, complications with APBI implant in a Medicare database review have been significant, with 3.95% of women requiring Mastectomy, 16.2% developing infections, and another 16.3% experiencing non-infection complications including rib fractures, fat necrosis, and breast pain. Recently APBI using non-invasive Intensity Modulated Radiation Therapy (IMRT) or SBRT given q.d. in 5 fractions has been shown in another randomized trial with 10-year follow-up to be equivalent to q.d. WBI in 6 weeks, with respect to LR. IMRT/SBRT was superior in regard to acute effects, late effects, and cosmesis. In the randomized clinical trial of APBI IMRT/SBRT, the Clinical Target Volume (CTV) was defined by the injection of individual fiducial markers bordering the surgical cavity. At our institution, we have used a bioabsorbable fiducial marker system to localize the CTV for SBRT. We sought to confirm the APBI IMRT/SBRT results with this simpler less labor-intensive fiducial placement system.Between 2017 and 2021, 218 patients have undergone SBRT targeted to a bioabsorbable fiducial marker defined CTV with the walls of the surgical cavity sewn to the fiducial marker. 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.Follow-up ranged from 1-39 months with a median of 20 months. LR has been 0% (0/218). There have been no skin reactions, seromas, or infections. Four (2.1%) patients developed pain around the fiducial marker 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 99.0% (216/218) of cases.Non-invasive APBI with SBRT given q.d. over 5 days targeted to bioabsorbable fiducial marker 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 99.0% of patients.