Prog Med Phys.  2019 Sep;30(3):65-73. 10.14316/pmp.2019.30.3.65.

Dosimetric Effects of Intrafractional Organ Motion in Field-in-Field Technique for Whole-Breast Irradiation

Affiliations
  • 1Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. sg.ju@samsung.com, doho.choi@samsung.com
  • 2Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea.

Abstract

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 (DHI(90/10)) for the target and Vâ‚‚â‚€ 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 DHI(90/10) values were observed between SFIF and DFIF (0.94 vs 0.95, P<0.05) in statistical analysis. The average Vâ‚‚â‚€ 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 motion-induced dosimetric errors.

Keyword

Dose variation; Field-in-field technique; Organ motion; Whole-breast irradiation
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