Feasibility of Postmastectomy Treatment With Helical TomoTherapy

Purpose: To investigate the potential of helical tomotherapy for postmastectomy radiation therapy. Methods and Materials: By use of the TomoTherapy Hi-Art II treatment-planning system (TomoTherapy Inc., Madison, WI), helical tomotherapy dose plans were developed for 5 patients and compared with the mixed-beam (electron-photon) plans with which they had been treated. The TomoTherapy plans were evaluated by use of dose-volume quantities, tumor control probability, normal tissue complication probability (NTCP), and secondary cancer complication probability (SCCP). Results: The TomoTherapy plans showed better dose homogeneity in the planning treatment volume containing the chest wall and internal mammary nodes (p = 0.001) and eliminated the need for abutting fields. For the normal tissues, the TomoTherapy plans showed a smaller fractional volume receiving 20Gy or greater for the ipsilateral lung (p = 0.05), no change in NTCP for postradiation pneumonitis, increased SCCP for each lung and both lungs together (p < 0.02), no change in the volume of the heart receiving more than 15Gy, no change in NTCP for excess cardiac mortality, and a larger mean dose and SCCP in the contralateral breast (p < 0.001). For nonspecific tissues, the volume receiving between 5Gy and 25Gy and SCCP were both larger for the TomoTherapy plans (p < 0.01). Total SCCP was larger for the TomoTherapy plans (p = 0.001). Conclusions: Overall, the TomoTherapy plans had comparable tumor control probability and NTCP to the mixed-beam plans and increased SCCP. The TomoTherapy plans showed significantly greater dose homogeneity in the chest wall, which offers the potential for improved cosmesis after treatment. These factors have resulted in TomoTherapy often being the treatment of choice for postmastectomy radiation therapy in our clinic.