Adjuvant partial breast radiotherapy (PBRT) is standard of care for early stage favorable breast cancer according to GEC-ESTRO, ASTRO, and ABS Guidelines. Modalities include both external bream and brachytherapy. We hypothesize that PBRT delivered by Low Dose Rate brachytherapy permanent breast seed implants (PBSI) as a single 2-hour procedure would be well received and well tolerated. From 07/12-10/18, 67 postmenopausal women with unifocal T1N0 invasive ductal breast cancer or DCIS, ER positive, negative margins, grade 1 or 2, and no LVI received PBRT using permanent implantation of stranded Pd-103 seeds on an REB approved Phase 2 trial. Following breast conserving surgery, PBSI delivered 90 Gy to the seroma + margin (1.25 to 1.5cm: max PTV 125 cc). Implants were planned with CT simulation and performed as an outpatient procedure under light anesthesia, guided by live ultrasound (US). Visualization of the seroma on both CT and US is essential. Post implant CT dosimetry used fusion with the original planning scan for seroma delineation. Evaluations were at 1, 2, 6, and 12 months and then annually. More than 95% of women suitable by oncologic criteria would consent to PBSI. Only about 40% are technically suitable due to seroma volume, location, or lack of visibility on CT or US. For 67 patients, median seroma volume was 6.6 cc (1.7-20.4), PTV 61 cc (31-117), # of needles 18 (10-30) and seeds 75 (42-134). In Day 0 dosimetry, median seroma D90 was 132 Gy (V100:97%), seroma+ 5mm 106 Gy (V100:93%) and seroma+10mm 80 Gy (V100:85%). Seroma location was 58% lateral, 31% anterior, 9% inframammary fold and one lower inner quadrant. The local reaction peaks at 6 weeks and is limited to the skin overlying the implant: 51% had grade 1 erythema, 12% superficial desquamation. Needle puncture marks are not visible at 4 weeks. Late reactions (> 2 years) are generally minimal: 35% no sequelae, 43% localized palpable asymptomatic fibrosis, 20% minimally apparent telangiectasia (6% more significant but asymptomatic), 22% slight lateral contour change or skin dimpling. All cases with more pronounced breast contour change (n=6) followed deforming surgery (nipple excision, marked post-operative nipple deviation, etc.). With a minimum of 6 months follow-up, 94% of respondents were “very satisfied” or “totally satisfied.” At a median follow up of 3.3 years (6-75 months), there has been one in-breast recurrence (different quadrant) detected at 12 months and treated with mastectomy at the patient’s request. Three patients have had biopsies of palpable fibrosis, all negative for malignancy. Two patients have had contralateral breast cancers, one of whom had partial mastectomy followed by a second PBSI, while the other opted for bilateral mastectomy for reasons of cancer anxiety despite satisfaction with the first procedure. Our experience with PBSI for PBRT is favorable with a high patient acceptance and satisfaction, excellent early efficacy and very satisfactory cosmesis.