Comparing Interfractional Stability of Heart Dose Among Three Breath-Hold Radiotherapy Techniques in Breast Cancer.

Aims: Breath holding can reduce the cardiac dose in radiotherapy for left-sided breast cancer. We evaluated whether any of the existing commonly used breath-hold techniques was superior in maintaining a more reproducible mean heart dose (MHD) during treatment.

Materials and methods: This was a single-institution, interventional, nonrandomised, three-armed prospective trial, comparing the reproducibility of MHD in breath-hold radiotherapy using voluntary deep inspiration breath hold (vDIBH), active breathing control (ABC), and surface-guided radiotherapy (SGRT). The MHDs were determined based on the anatomy in planning computed tomography (CT) and each weekly cone beam computed tomography (CBCT) during radiotherapy. The reproducibility of MHD was measured by calculating the interfractional variation of MHD (represented by the standard deviation) across the CBCT and the difference between the cumulative MHD at CBCT and at planning CT. These two measures of reproducibility were then compared among vDIBH, ABC, and SGRT.

Results: Of the 55 patients recruited, 19 had ABC, 20 had SGRT, and 16 had vDIBH. SGRT was associated with a slightly greater interfractional variation of the MHD than vDIBH (least squares mean (LSM): 28.8 cGy (SGRT) vs 10.5 cGy (vDIBH), P = 0.0052) and ABC (LSM: 28.8 cGy (SGRT) vs 15.1 cGy (ABC), P = 0.026). In the SGRT group, the cumulative MHD at CBCT was lower than that at planning CT (mean difference: -22.1 cGy, P = 0.013). No such difference existed in vDIBH and ABC. In terms of the reproducibility of cumulative MHD at CBCT as compared to that in planning CT, there was no significant difference between vDIBH (mean: -12.1 cGy), ABC (mean: -4.8 cGy), and SGRT (mean: -22.1 cGy) (P value for pairwise comparison: all >0.1).

Conclusions: SGRT was associated with a slightly greater interfractional variation of MHD than vDIBH and ABC, but the difference may not be clinically significant. All three breath-hold techniques were broadly comparable in their reproducibility of MHD at CBCT relative to the planning CT.