Dosimetric Impact of Respiratory Motion During Breast Intensity-modulated Radiation Therapy Using Four-dimensional Dose Calculations.

Background/aim: The use of intensity-modulated radiation therapy (IMRT) in the treatment of breast cancer is increasing worldwide. Despite clear benefits concerning normal tissue sparing and dose homogeneity, the effects of breathing motion and setup error during breast IMRT should be considered. This study aimed to assess the dosimetric impact of respiratory motion on breast IMRT using four-dimensional (4D) dose calculations.

Patients And Methods: Multiple computed tomography datasets acquired in three representative respiratory amplitudes, were retrospectively re-planned. Based on the reference dose distribution (RDD), motion-adjusted dose distributions (MDD) were recalculated. All 4D dose distributions were calculated by the voxel-based accumulation of RDD and MDD using five temporal probabilities. The dosimetric parameters of the 4D plans were compared to those of RDD.

Results: The dosimetric parameters of the planning target volume (PTV) were not significantly different between the RDD and 4D plans. Of the parameters of tumor bed (TB) simultaneous-integrated boost (SIB), the mean dose and V for the 4D plans were significantly reduced compared to those of RDD, and the percentage difference in the TB V ranged from -1.1% to -5.7% (p<0.05).

Conclusion: The breast IMRT plan was robust against respiratory motion during tidal breathing. However, special considerations should be made when designing the TB SIB.