Comparison of heart dose in early-stage left-sided breast cancers treated with intraoperative radiation therapy or whole-breast irradiation with deep inspiratory breath hold

Purpose: To compare heart dose between patients treated with lumpectomy and either intraoperative radiation therapy (IORT) with CT-guided high-dose-rate brachytherapy (precision breast IORT [PB-IORT]) or whole-breast irradiation with deep inspiratory breath hold (WBI-DIBH) for early-stage left-sided breast cancers.

Methods and materials: We retrospectively identified the 17 patients with left-sided breast cancers treated with PB-IORT on a phase I clinical trial and 17 patients with left-sided tumors who had undergone lumpectomy and adjuvant WBI-DIBH. Dosimetric data were obtained. T-testing was performed and biologically effective doses (BEDs) were calculated using an α/β ratio of 2 Gy.

Results: Mean heart dose was significantly lower with WBI-DIBH compared with PB-IORT (0.61 vs. 0.87 Gy, p = 0.006). Mean heart BED was lower with WBI-DIBH (0.62 vs. 1.3 Gy₂, p = 0.0001). Nominal maximum heart dose was higher with WBI-DIBH (11.37 vs. 4.81 Gy, p = 0.004). Maximum heart dose BED was similar between WBI-DIBH and IORT, 16.63 vs. 19.36 Gy (p = 0.64), respectively. No difference was found in mean left anterior descending artery dose: 2.18 Gy with WBI-DIBH and 1.89 Gy with IORT (p = 0.446). The maximum left anterior descending doses were 9.63 Gy and 3.62 Gy with WBI-DIBH and IORT, respectively (p = 0.016). Distance from the heart to the lumpectomy cavity was inversely associated with heart dose for PB-IORT, but not for WBI-IORT.

Conclusions: Heart doses were low in both groups. Expected increase in cardiac risk at these doses is minimal. It is unlikely that there will be a clinically significant difference in cardiac toxicity in patients treated with WBI-DIBH or PB-IORT. Further research is needed to evaluate the actual clinical impact of the observed cardiac doses delivered with these modalities.