External-Beam Partial Breast Irradiation: The New York University Prone Technique

Partial breast irradiation performed using external-beam techniques in the prone position has many advantages. In addition to the many advantages associated with the use of a hypofractionated regimen delivered by an external beam, positioning the patient in the prone position often displaces the tumor bed target away from the chest wall, enabling better sparing of lungs and heart. Originally developed at the University of Southern California, prone external-beam partial breast irradiation (prone EB-PBI) was further perfected at New York University, and has confirmed its feasibility and convenience to the patient. Some of the advantages associated with the technique we have developed have resulted in a significant reduction in interfraction variability. For instance, the advantage of using only five fractions also demands very accurate alignment during treatment. Moreover, since the utilization of prone positioning drastically reduces the intrafraction movement associated with respiration, it has been possible to reduce the margins of the planning target volume (PTV), which requires high targeted delivery precision. To address this challenge of precise positioning, our group has pilot-tested the use of image-guided prone EB-PBI. This review describes the clinical evolution of prone EB-PBI and introduces preliminary experiences of using cone-beam CT image guidance with the Varian On-Board Imager kV imaging system daily.