Investigation of helical tomotherapy for partial-breast irradiation of prone-positioned patients.

Abstract

To investigate whether helical tomotherapy can provide conformal, uniform target-dose coverage for partial-breast irradiation (PBI) of patients positioned prone while achieving organ-at-risk sparing compliant with National Surgical Adjuvant Breast and Bowel Project (NSABP) B-39/Radiation Therapy Oncology Group (RTOG) 0413 guidelines; and to report our initial experience with the delivery of prone-breast PBI treatments using tomotherapy. For our pilot study, we generated helical tomotherapy plans upon the images of 10 prone-positioned patients previously treated using conventional techniques. We also generated plans for 4 left-breast prone-positioned PBI patients who were treated using helical tomotherapy, and recalculated the planned sinograms upon the pretreatment megavoltage computed tomographic images. Of the planning target volume (PTV), 95% was prescribed to receive 38.5 Gy, administered twice daily for 5 days. For our pilot study, on average the maximum point dose to the PTV was 41.3 Gy, and 99% or more of the PTV received 90% or more of the prescribed dose. RTOG 0413 dose-volume histogram objectives were fulfilled for all organs at risk except the contralateral breast, which received a maximum point dose as high as 3.2 Gy in 1 case. For the prospective prone-positioned tomotherapy PBI plans, all objectives were met except the contralateral-breast maximum dose, which was 3.7 Gy on average. Dose calculation using the planned sinogram upon the pretreatment megavoltage computed tomographic images indicated consistency with the planned dose distributions. Helical tomotherapy can provide conformal and uniform target-dose coverage simultaneous with adequate sparing of critical structures; in this study only the contralateral breast dose exceeded RTOG 0413 guidelines. Dosimetric results for our 4 prospective patient cases were consistent with those for our 10-case pilot study.