Session Item

This study aimed to assess radiation dose distribution to coronary arteries and cardiac chambers in bilateral breast cancer irradiation.

Forty patients referred for bilateral breast cancer RT were evaluated. All patients underwent hypofractionated 3D conformal RT, using a mono-isocentric technique, with a prescription dose of 40 Gy/15 fractions +/- an additional boost of 13.35 Gy. Cardiac chambers (Left ventricle (LV), left atrium (LA), right ventricle (RV), right atrium (RA)) and coronary arteries (left main (LM), left circumflex (LCx), left anterior descending (LAD), right coronary artery (RCA)) were contoured according to the Duane’s cardiac contouring atlas. Dose-volume histograms were generated for all cardiac subvolumes. The following dosimetric parameters were assessed: mean heart dose (MHD), V5Gy, V20Gy, V25Gy to the heart, Dmean and Dmax to each cardiac substructure, V40Gy, V30Gy to the LAD, V5Gy and V23Gy to the LV.

The mean age was 52 (27-77) years. Thirty-five percent of patients had at least one cardiovascular risk factor and 64% received anthracyclines based chemotherapy. Radiotherapy was delivered to the thoracic wall in 54% and 45%, and to the remaining breast in 46% and 55% of patients, respectively for the right and left-sided breast cancer irradiation. Bilateral internal mammary chain (IMC) RT was performed in 36% of cases. The mean MHD was 3.62 (EQD2=4.11) Gy, ranging between 1.92 and 5.93 Gy. Dose constraints to the heart (V5Gy, V20Gy and V25Gy) were respected in all treatment plans, except for one bilateral locoregional RT including the IMC where the V25Gy heart was 14.8%. The mean Dmax/Dmean were 3.52 (1.18-14.4) Gy / 2.38 (1.1-14.09) Gy and 5.82 (2.7-29.68) Gy/ 2.79 (1.95-9.1) Gy, respectively for the LM and RCA. Mean Dmax/Dmean to the LAD was 30.38 (2.19-49.14) Gy / 11.83 (3.17-30.95) Gy. The V40Gy to the LAD was above 1% for 13 patients, whereas V30Gy exceeded 2% in 50% of cases, reaching 30% for two patients. The mean Dmax to the LCx was 2.55 (1.25-14.9) Gy. High doses were delivered to the ventricles with mean Dmax/Dmean of 38.99 (5.05-51.1) Gy / 4.68 (2.04-7.69) Gy and 20.6 (4.74-36.53) Gy / 3.17 (2.15-5.55) Gy, respectively for the LV and RV. The V5Gy to the LV was above 17% for 25 patients (62.5%) and the V23 Gy to the LV exceeded 5% in 60% of cases.

Bilateral breast cancer RT yielded substantially high doses to all cardiac subvolumes. High point doses were reported to the LM and coronary arteries’ proximal segments, which are usually spared in unilateral breast cancer radiotherapy. Considering the potentially harmful subsequent clinical outcomes, bilateral breast cancer RT should be regarded as a high cardiac risk irradiation and heart sparing techniques should be used.