Detection of Intrafractional Set-Up Errors Using Electronic Portal Imaging Device-based in vivo Dosimetry in...

This study aimed to clarify the relationship between the results of in vivo dosimetry (IVD) analysis and intrafractional set-up errors (SEs) to determine the criteria for detecting intra-fractional SEs of 3 mm.

Fifteen patients undergoing deep-inspiration breath-hold (DIBH) irradiation for left breast cancer were included in the study. The prescribed dose and fraction size were 50 Gy for six patients, and 42.56 Gy for nine patients. Visual coaching devices were used to improve the reproducibility of deep inspiration states. For IVD, integrated electronic portal imaging device (EPID) images were obtained using treatment beams. Intra-fractional SEs were detected, and gamma analysis was performed on these images. Receiver-operating characteristic curves were calculated to assess the accuracy of the detection of the intrafractional SEs for each criterion.

The mean values for two-dimensional vectors, absolute Z-direction, and three dimensional (3D) vectors of intra-fractional SEs were 1.9 ± 1.5 mm, 1.8 ± 1.6 mm, and 2.9 ± 1.8 mm, respectively. The mean γ-pass rates in each criterion were 90.6% ± 10.4%, 89.6% ± 10.8%, 92.7% ± 9.7%, 94.8% ± 8.3%, and 94.4% ± 8.3% for 2% 3 mm, 3% 2 mm, 3% 3 mm, 3% 4 mm, and 4% 3 mm, respectively. The correlation coefficients between the SEs in the 3D vector and each γ value ranged from 0.6 to 0.8.

In IVD with EPIDs for DIBH irradiation, the optimal γ-analysis index for intrafractional SEs detection >3 mm is 3% 3 mm.