Cardiac dose in the treatment of synchronous bilateral breast cancer patients between three different radiotherapy techniques (VMAT, IMRT, and 3D CRT)

PURPOSE: Synchronous bilateral irradiation of both mammary glands and chest wall is a challenging task due to technical difficulties and limited evidence supporting an optimal technique to improve treatment outcomes. We studied and compared the dosimetry data of three radiotherapy techniques to select the most optimal one. METHODS: We compared three-dimensional conformal radiation treatment (3D CRT), intensity-modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT) during irradiation of synchronous bilateral breast cancer in nine patients followed by examination of dose distribution to the cardiac conduction system (SA node, AV node and Bundle of His), myocardium, lungs, left anterior descending artery (LADA) and right coronary artery (RCA) . RESULTS: VMAT is the most sparing technique for SBBC treatment. Even though doses to the SA node, AV node and Bundle of His were higher with VMAT (D(mean) were 3.75 ± 0.62, 2.58 ± 0.83 and 3.03 ± 1.18 Gy respectively) compared with 3D CRT (D(mean) were 2.61 ± 0.66, 1.52 ± 0.38 and 1.88 ± 0.70 Gy respectively), this difference is statistically insignificant. Doses to the right and left lung (average D(mean) = 12.65 ± 3.20 Gy, V(20Gy) = 24.12 ± 6.25%), myocardium (D(mean) = 5.33 ± 1.51 Gy, V(10Gy) = 9.80 ± 3.83%, V(20Gy) = 7.19 ± 3.15%, V(25Gy) = 6.20 ± 2.93%), and LADA (D(mean) = 10.04 ± 4.92 Gy, V(20Gy) = 18.17 ± 13.24% and V(25Gy) = 15.41 ± 12.19%) were highest with 3D CRT. The highest D(mean) in the cardiac conduction system (5.30 ± 2.23, 3.15 ± 1.61 and 3.89 ± 1.85 Gy respectively) was observed with IMRT, and a similar effect was noted in RCA (D(mean) = 7.48 ± 2.11 Gy). CONCLUSION: VMAT is the optimal and satisfactory radiation therapy technique for sparing organs at risk (OARs). With VMAT, a lower D(mean) value was noted in the myocardium, LADA, and lungs. The use of 3D CRT significantly increases the dose of radiation reaching the lungs, myocardium, and LADA, which can subsequently cause cardiovascular and lung complications, but not in the cardiac conduction system.