Intensity modulated radiation therapy (IMRT) reduces the dose to the contralateral breast when compared to conventional tangential fields for primary breast irradiation

Abstract

To determine the dose received by the contralateral breast during primary breast irradiation using IMRT compared to conventional radiation techniques. Between March 2003 and March 2004, 83 patients with breast carcinoma were treated using 6, 10, or mixed 6/18 MV photons (65 patients with tangential IMRT technique using Eclipse® Planning System (Varian Medical Systems, Palo Alto, CA) and 18 patients with 2-dimensional technique using tangential fields with wedges) for primary breast irradiation following breast conserving surgery. Paired thermoluminescent dosimeters (TLDs) were placed on each patient’s contralateral breast, four and eight centimeters (cm) from the center of the medial border of the tangential field. The TLDs were left on the patient during a single fraction of radiation and then measured 24 hours afterwards using the Harshaw model 5500 TLD reader (Bicron, Solon, Ohio). The paired TLDs were averaged for each patient and a variance of less than three percent was required in order to be included for analysis. Using SPSS software, a two tailed T-Test was used to compare the contralateral breast dose for patients treated with IMRT versus conventional radiation technique. The mean dose delivered with photons to the primary breast for all patients was 4999 centigray (cGy) [SD = 52 cGy] with a mean single fraction dose of 199 cGy [SD = 8 cGy]. The mean percent of the prescribed dose to the contralateral breast measured at the 4 and 8 cm positions were 7.19% [SD = 2.28] and 4.63% [SD = 2.12], respectively, for patients treated with IMRT compared to 11.22% [SD = 2.73] and 10.70% [SD = 3.44], respectively, for the patients treated with conventional tangential fields. This represented a 36% and 57% reduction at the 4 and 8 cm contralateral positions, respectively, in the mean dose to the contralateral breast using IMRT compared to the conventional technique which was statistically significant (p < 0.0005 and p < 0.0005, respectively). This study suggests that primary breast irradiation with tangential IMRT technique significantly reduces the dose to the contralateral breast compared to standard radiation techniques