Multileaf field-in-field forward-planned intensity-modulated dose compensation for whole-breast irradiation is associated with reduced contralateral breast dose: A phantom model comparison

Purpose: Static multileaf collimated field-in-field forward-planned intensity-modulated radiation treatment (FiF-IMRT) has been shown to improve dose homogeneity compared to conventional wedged fields. However, a direct comparison of the scattered dose to the contralateral breast resulting from wedged and FiF-IMRT plans remains to be documented. Methods: The contralateral scattered breast dose was measured in a custom-designed anthropomorphic breast phantom in which 108 thermoluminescent dosimeters (TLDs) were volumetrically placed every 1-2 cm. The target phantom breast was treated to a dose of 50 Gy using three dose compensation techniques: No medial wedge and a 30-degree lateral wedge (M0-L30), 15-degree lateral and medial wedges (M15-L15), and FiF-IMRT. TLD measurements were compared using analysis of variance. Results: For FiF-IMRT, the mean doses to the medial and lateral quadrants of the contralateral breast were 112 cGy (range 65-226 cGy) and 40 cGy (range 18-91 cGy), respectively. The contralateral breast doses with FiF-IMRT were on average 65% and 82% of the doses obtained with the M15-L15 and M0-L30 techniques, respectively (p < 0.001). Compared to the M15-L15 technique, the maximum dose reduction obtained with FiF-IMRT was 115 cGy (range 13-115 cGy). Conclusions: The dose to the contralateral breast is significantly reduced with FiF-IMRT compared to wedge-compensated techniques. Although long-term follow-up is needed to establish the clinical relevance of this finding, these results, along with the previously reported improvement in ipsilateral dose homogeneity, support the use of FiF-IMRT if resources permit.