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

PURPOSE: 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.

METHODS AND MATERIALS: 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.

RESULTS: 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.

CONCLUSIONS: 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.