Assessment of deep inspiration breath hold technique setup reproducibility using mega voltage imaging for left breast cancer radiation therapy-integrated network study.

We evaluated daily setup reproducibility of deep inspiration breath hold (DIBH) using mega voltage (MV) imaging for left breast cancer radiation therapy. Analysis of 109 left breast cancer patients across UPMC Hillman Cancer Center network treated using DIBH technique with daily MV imaging was done. Patient characteristics, MV imaging procedure used and inter-fraction directional shifts were collected. For the statistical analyses, we separated all patients into 2 groups in each of the following 3 categories; (1) obese (BMI ≥ 30) vs nonobese, (2) mastectomy vs lumpectomy, (3) internal mammary node (IMN) treatment vs no IMN treatment. The group mean inter-fraction directional shifts were as following: (1) 0.7 mm (superior), 0.8 mm (inferior); (2) 0.65 mm (left), 0.64 mm (right); (3) 0.89 mm (anterior), 0.83 mm (posterior). Also, any directional shift ≥ 2 mm, ≥ 3 mm, ≥ 4 mm, ≥ 5 mm, ≥ 10 mm was found to be 52.9%, 37.6%, 30.9%, 21.9%, 3.7% of total fractions, respectively. In the stratified analysis, obese patients had larger directional shifts (p < 0.05) and highly associated with number of fractions for ≥ 5 mm in any directional shift compared to nonobese patients (29% vs 17%; p = 0.04). DIBH setup for left breast cancer treatment at our large cancer center network was reproducible with any mean directional shifts less than 1.0 mm using MV imaging. Daily imaging would be more beneficial for obese patients compared to nonobese patients.