Accelerated partial breast irradiation: Use of four-dimensional CT for target localization and assessment of...

The aim of this study was to use four-dimensional CT (4DCT) in the planning of 3D conformational external beam radiation therapy (3DCRT) for patients with early stage breast cancer. A total of nine Chinese women who received breast conservation treatment were included in this study. Target localization and movement (range of motion) during normal respiration were assessed using ultrasound and 4DCT. Plans based on 3DCT and 4DCT scans were developed in accordance to RTOG0319 guidelines and dose delivery comparisons were made between these plans. The mean ranges of motion of the excision cavity volume as determined using 4DCT were 1.03 +/- 0.51, 2.08 +/- 0.92, and 1.27 +/- 0.58 mm in the right-left, anterior-posterior, and superior-interior directions, respectively. There were no significant differences between the mean and maximum PTV-E doses or the volume receiving 95% of the prescribed dose (V95). 4D plan prescribed dose levels were significantly lower (p < 0.05) than 3D plan levels for all of the following: ipsilateral breast V100, ipsilateral lung V30, and contralateral lung V5. Maximum contralateral breast and thyroid doses were also significantly lower with the 4D plan (p < 0.05). This study highlights the usefulness of 4DCT for the planning of 3DCRT in breast cancer patients. Our findings suggest that the use of 4DCT can lead to improvements in target definition and decreases in normal tissues irradiation.