Abstract P1-15-22: Comparison of cardiac dose between accelerated partial-breast irradiation and whole-breast irradiation in breast cancer patients
Authors: Sato Kazuhiko , Mizuno Yoshio , Fuchikami Hiromi , Takeda Naoko , Shimo Takahiro , Kubota Jun , Inoue Yuko , Seto Hiroshi , Kato Masahiro 
Published: May 2015

Abstract
[Background] Breast-conserving surgery (BCS) followed by whole-breast irradiation (WBI) has now become the standard treatment for early-stage breast cancer. However, WBI is associated with an increased risk of coronary events, especially in patients with preexisting cardiac risk factors. In radiotherapy (RT), the highest dose is likely delivered to the left anterior descending artery (LAD), which is the typical site for ischemic heart disease. We initiated a prospective, observational study on accelerated partial-breast irradiation (APBI) using multicatheter brachytherapy after BCS. In this study, we compared the radiation dose to LAD between patients receiving APBI and those receiving WBI.
[Methods] The study participants included a cohort selected from consecutive patients who underwent BCS followed by RT since November 2007. In the WBI group, patients received 50 Gy in fractions of 2 Gy to the entire breast. APBI was initiated on the day of primary surgery in the form of multicatheter brachytherapy, at a dose of 32 Gy in 8 fractions. The planned target volume was defined as the estimated tumor volume plus a 20-mm margin. Dose distribution analysis was performed on the basis of postoperative CT using dose–volume histograms. LAD was outlined from its origin to each visible end using the planning CT images. First, the mean and maximal total doses to LAD were calculated. Second, the radiotherapeutic biologically effective dose of APBI was adjusted to that of WBI for comparisons between the two different RT schedules.
[Results] Of the 359 consecutive patients who underwent BCS followed by RT, we retrospectively reviewed 182 patients for radiation dose to LAD. The 82 patients receiving WBI were randomly selected; 42 patients had right breast cancer and 40 had left breast cancer. We selected 100 consecutive APBI patients with left breast cancer treated between September 2009 and December 2013 because the LAD dose is considered to be virtually zero in right breast cancer patients. In the WBI patients, the mean and maximal total LAD dose were significantly higher in left breast cancer patients (2.1 ± and 8.2 ± 1.2 Gy, respectively) than in right breast cancer patients (0.4 ± 0.02 and 0.6 ± 0.03 Gy, respectively; p &lt; 0.0001). Among the APBI patients, the total LAD doses were influenced by tumor location. The mean and maximal total LAD doses were significantly higher in patients with inner quadrants or central tumors (2.5 ± 0.2 and 4.4 ± 2.5 Gy, respectively) than in those with outer quadrant tumors (1.0 ± 0.1 and 2.1 ± 0.3 Gy, respectively; p &lt; 0.0001). After adjustment for the total LAD dose, the mean and maximal total LAD doses were significantly decreased in APBI patients with outer quadrant tumors (1.1 ± 0.2 and 2.4 ± 0.4 Gy, respectively; p &lt; 0.0001), but not in those with central and inner quadrant tumors (2.9 ± 0.3 and 5.4 ± 0.6 Gy, respectively).
[Conclusions] Our results show that APBI may decrease the risk of coronary artery disease, especially in patients with outer quadrant tumors in the left breast. Although APBI should be carefully interpreted until mature phase-III data are available, the risk of ipsilateral breast tumor recurrences and LAD dose must be considered together while administering RT after BCS.
Citation Format: Kazuhiko Sato, Yoshio Mizuno, Hiromi Fuchikami, Naoko Takeda, Takahiro Shimo, Jun Kubota, Yuko Inoue, Hiroshi Seto, Masahiro Kato. Comparison of cardiac dose between accelerated partial-breast irradiation and whole-breast irradiation in breast cancer patients [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-15-22.