Introduction: Radiotherapy (RT) may increase the dose of heart structure like left anterior descending coronary artery (LAD). The purpose of this paper was to evaluate the impact of various multileaf collimators (MLCs) in shielding organ at risks (OARs), especially LAD, of patients with left breast cancer.
Materials and methods: Forty-five patients with left breast cancer were selected. The treatment plans were created applying three techniques for all patients. In the first plan (uncovered LAD), the treatment plan was made without considering LAD as OARs. In the two other plans, two MLCs with different leaf widths (6.8 mm and 5 mm) were used to shield the LAD. For all plans, MLC was shielded as much of OAR as possible without compromising planning target volume (PTV) coverage. Dosimetric parameters of the heart, LAD, and ipsilateral lung were assessed.
Results: Compared to other plans, the covered LAD plan 1(CL1) obtained lower lung, cardiac, and LAD doses with the same PTV coverage. On average, the mean heart dose decreased from 6.2 Gy to 5.4 Gy by CL1, and the average mean dose to the LAD was reduced from 36.4 Gy to 33.7 Gy, which was statistically significant. The average lung volume receiving >20 Gy was significantly reduced from 24.6% to 23.4%. Moreover, the results show that covered LAD plan 2(CL2) is less useful for shielding OARs compared to CL1.
Conclusion: CL1 plans may reduce OAR dose for patients without compromising the target coverage. Hence, the proper implementation of MLC can decrease the side effects of RT.
Keywords: Left anterior descending coronary artery; left breast cancer; multileaf collimator; organs at risk; radiotherapy.