Prospective Trial on the Impact of Weekly Cone Beam Computed Tomography-Guided Correction on Mean Heart Dose in Breast Cancer Breath-Hold Radiation Therapy.

Purpose: Surface guided radiation therapy (SGRT) in breast cancer radiation therapy (RT) may decrease the need for image guidance such as cone beam computed tomography (CBCT). The goal of this study was to evaluate the impact of CBCT image guidance on the cumulative and interfractional variation of mean heart dose (MHD) during breath-hold RT in patients with breast cancer. We hypothesized that weekly CBCT is not necessary for SGRT-assisted breath-hold but is still needed in patients treated with voluntary deep inspiration breath-hold (vDIBH) and active breathing control (ABC) to maintain a stable MHD.

Methods And Materials: This was a prospective, single-center trial that sequentially assigned breast cancer patients to adjuvant RT 40 to 50 Gy in 15 to 25 fractions using vDIBH, ABC, or SGRT to reproduce the breath-hold. The MHD was estimated on each of the weekly CBCT images before and after online correction. The cumulative and interfractional variation of MHD, which were represented by the average and SD of MHD in each patient, were compared in the series of CBCT before and after online correction to evaluate whether online CBCT-guided correction could lead to a more reproducible MHD.

Results: Fifty-five patients were included (vDIBH = 16, ABC = 19, and SGRT = 20). The CBCT-guided online correction was associated with a significant decrease in the interfractional variation of MHD in vDIBH (SD difference, 22.6 cGy; = .0389) and ABC (SD difference, 9.9 cGy; = .0262), but not in SGRT ( = .2272). The CBCT-guided online correction had no impact on the cumulative MHD in all 3 groups.

Conclusions: This study demonstrated that CBCT-guided online correction could reduce the interfractional variation of MHD in ABC or vDIBH. When SGRT was available, CBCT-guided correction had no impact on the stability of MHD across the treatment fractions. Future studies may explore whether the CBCT frequency could be reduced to less than weekly in SGRT to decrease treatment time and the radiation dose associated with CBCT.