Oral Scientific SessionsStereotactic Body Radiation Therapy for Early-Stage Breast Cancer Using a Robotic Linear Accelerator

Standard radiation therapy for patients with breast cancer desiring breast conservation typically consists of lumpectomy followed by radiation. Radiation can either be delivered to the whole breast or to part of the breast. Whole breast radiation is typically given daily for 3-6 weeks depending on the dose/fractionation scheme. When partial breast irradiation is provided, an implanted catheter is often used to deliver a conformal treatment to the lumpectomy cavity in an accelerated manner over one week. In properly selected patients, the results for partial breast irradiation appear comparable to results for conventional whole breast radiation. We examined the safety and efficacy of using an accelerated dose/fractionation schedule with a robotic linear accelerator for select patients with early stage breast cancer after lumpectomy. Herein we report our multi-institutional results. Sixty-three consecutive patients with early stage breast cancer were enrolled on an institutional review board approved protocol at two academic hospitals. Eligibility included Stage 0/I/II (< 3 cm), Age >45, negative margins. Most (41) fiducial markers were placed by the treating radiation oncologist, utilizing image guidance on a CT simulator with coordinate placement determined by the physics staff for optimal localization. The remainder was placed by the surgeon at the time of lumpectomy. Patients were immobilized either using a thermoplastic cast or with an alpha cradle to allow the breast to remain in its natural position. All patients were treated with non-isocentric robotic SBRT using real-time tracking of the implanted fiducials. The mean prescription was 3000 cGy (range: 2500- 3600) delivered in 5 (range: 5-10) consecutive daily fractions. The median prescription isodose line was 71% (range: 65-76%). The mean PTV for the whole group was 114 cm3 (range 39-241 cm3). With a median follow-up of 46 months, (range: 2-91), 62 of 63 patients (98.3%) remain locally controlled with no evidence of disease following treatment. One patient developed a local recurrence 18 months after radiation and was treated with mastectomy and remains without evidence of disease. Minimal erythema involving a small portion of the breast was reported by 2 patients and one patient experienced pain at the lumpectomy site 10 months post treatment. RTOG Grade 1 dry skin desquamation occurred in 1 of 63 patients. The cosmesis was good-excellent in all 62 patients using the Harvard cosmesis scale. Stereotactic Body Radiation Therapy for patients with early stage breast cancer desiring breast conservation therapy can be delivered safely with a robotic linear accelerator. Treatment is well tolerated and efficacious for well selected patients in this multi-institutional cohort. More accrual and longer duration of follow-up will be required to see if these results remain durable.