title: Stereotactic Accelerated Partial Breast Irradiation for Early-Stage Breast Cancer: Rationale, Feasibility, and Early Experience Using the CyberKnife Radiosurgery Delivery Platform.
abstract: OBJECTIVE
  The efficacy of accelerated partial breast irradiation (APBI) utilizing brachytherapy or conventional external beam radiation has been studied in early-stage breast cancer treated with breast-conserving surgery. Data regarding stereotactic treatment approaches are emerging. The CyberKnife linear accelerator enables excellent dose conformality to target structures while adjusting for target and patient motion. We report our institutional experience on the technical feasibility and rationale for stereotactic accelerated partial breast irradiation (SAPBI) delivery using the CyberKnife radiosurgery system.
  
  
  METHODS
  Ten patients completed CyberKnife SAPBI (CK-SAPBI) in 2013 at Georgetown University Hospital. Four gold fiducials were implanted around the lumpectomy cavity prior to treatment under ultrasound guidance. The synchrony system tracked intrafraction motion of the fiducials. The clinical target volume was defined on contrast enhanced CT scans using surgical clips and post-operative changes. A 5 mm expansion was added to create the planning treatment volume (PTV). A total dose of 30 Gy was delivered to the PTV in five consecutive fractions. Target and critical structure doses were assessed as per the National Surgical Adjuvant Breast and Bowel Project B-39 study.
  
  
  RESULTS
  At least three fiducials were tracked in 100% of cases. The Mean treated PTV was 70 cm(3) and the mean prescription isodose line was 80%. Mean dose to target volumes and constraints are as follows: 100% of the PTV received the prescription dose (PTV30). The volume of the ipsilateral breast receiving 30 Gy (V30) and above 15 Gy (V > 15) was 14 and 31%, respectively. The ipsilateral lung volume receiving 9 Gy (V9) was 3%, and the contralateral lung volume receiving 1.5 Gy (V1.5) was 8%. For left-sided breast cancers, the volume of heart receiving 1.5 Gy (V1.5) was 31%. Maximum skin dose was 36 Gy. At a median follow-up of 1.3 years, all patients have experienced excellent/good breast cosmesis outcomes, and no breast events have been recorded.
  
  
  CONCLUSIONS
  CyberKnife stereotactic accelerated partial breast irradiation is an appealing technique for partial breast irradiation offering improvements over existing APBI techniques. Our early findings indicate that CK-SAPBI delivered in five daily fractions is feasible, well tolerated, and is a reliable platform for delivering APBI.
authors.affiliation: Department of Radiation Medicine, Lombardi Comprehensive Cancer Center, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Olusola
authors.initials: O
authors.lastname: Obayomi-Davies
authors.affiliation: Department of Radiation Medicine, Lombardi Comprehensive Cancer Center, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Kole
authors.affiliation: Betty Lou Ourisman Breast Health Center, Lombardi Comprehensive Cancer Center, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Bridget
authors.initials: B
authors.lastname: Oppong
authors.affiliation: Department of Radiation Medicine, Lombardi Comprehensive Cancer Center, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Sonali
authors.initials: S
authors.lastname: Rudra
authors.affiliation: Department of Radiology, MedStar Georgetown University Hospital , Washington, DC , USA.
authors.forename: Erini V
authors.initials: EV
authors.lastname: Makariou
authors.affiliation: Department of Radiation Medicine, Lombardi Comprehensive Cancer Center, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Lloyd D
authors.initials: LD
authors.lastname: Campbell
authors.affiliation: Department of Radiation Medicine, Lombardi Comprehensive Cancer Center, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Hozaifa M
authors.initials: HM
authors.lastname: Anjum
authors.affiliation: Department of Radiation Medicine, Lombardi Comprehensive Cancer Center, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Sean P
authors.initials: SP
authors.lastname: Collins
authors.affiliation: Department of Radiation Medicine, Lombardi Comprehensive Cancer Center, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Keith
authors.initials: K
authors.lastname: Unger
authors.affiliation: Betty Lou Ourisman Breast Health Center, Lombardi Comprehensive Cancer Center, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Shawna
authors.initials: S
authors.lastname: Willey
authors.affiliation: Betty Lou Ourisman Breast Health Center, Lombardi Comprehensive Cancer Center, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Eleni
authors.initials: E
authors.lastname: Tousimis
authors.affiliation: Department of Radiation Medicine, Lombardi Comprehensive Cancer Center, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Collins
keywords: APBI; CyberKnife breast; breast SBRT; breast cancer; breast radiosurgery; partial breast irradiation; stereotactic radiosurgery