Purpose: We evaluated the motion-induced dosimetric effects on the field-in-field (FIF) technique
for whole-breast irradiation (WBI) using actual patient organ motion data obtained from cine
electronic portal imaging device (cine EPID) images during treatment.
Materials and Methods: Ten breast cancer patients who received WBI after breast-conserving
surgery were selected. The static FIF (SFIF) plan involved the application of two parallel opposing
tangential and boost FIFs. To obtain the amplitude of the internal organ motion during treatment,
cine EPID images were acquired five times for each patient. The outside contour of the breast
(OCB) and chest wall (CW) contour were tracked using in-house motion analysis software.
Intrafractional organ motion was analyzed. The dynamic FIF (DFIF) reflecting intrafractional organ
motion incorporated into the SFIF plan was calculated and compared with the SFIF in terms of the
dose homogeneity index (DHI90/10) for the target and V20 for the ipsilateral lung.
Results: The average motion amplitudes along the X and Y directions were 1.84±1.09 mm and
0.69±0.50 mm for OCB and 1.88±1.07 mm and 1.66±1.49 mm for CW, respectively. The
maximum motion amplitudes along the X and Y directions were 5.53 and 2.08 mm for OCB and
5.22 and 6.79 mm for CW, respectively. Significant differences in DHI90/10 values were observed
between SFIF and DFIF (0.94 vs 0.95, P<0.05) in statistical analysis. The average V20 for the lung in
the DFIF was slightly higher than that of the SFIF in statistical analysis (19.21 vs 19.00, P<0.05).
Conclusion: Our findings indicate that the FIF technique can form a safe and effective treatment
method for WBI. Regular monitoring using cine EPID images can be effective in reducing motioninduced
dosimetric errors.