Multileaf collimator shielding technique to reduce cardiac dose in hybrid intensity modulated radiotherapy after breast conserving surgery for left-sided breast cancer

Objective: To reduce the risk of radiation-induced cardiac injury in patients with left breast cancer after breast-conserving surgery by multileaf collimator (MLC) shielding technique. Methods: A total of 18 patients with left breast cancer after breast conserving surgery were selected to obtain 3DCT and 4DCT images at free breathing state. The target area was identified on the 3DCT image by registration with 4DCT images and to develop a hybrid intensity-modulated treatment plan (H_IMRT) and a heart sparing hybrid intensity-modulated treatment plan (HSH_IMRT) to introduce MLC shielding technology to reduce the cardiac exposure dose, and to perform dosimetry verification of the treatment plan by using the Compass verification system. The prescription dose was 50 Gy in 25 fractions. The dosimetry parameters of the target area and the organs at risk were compared between the two treatment plans and the dose verification result. Results: The result of the treatment plan showed that compared with H_IMRT, the dose uniformity of the target area of HSH_IMRT was better, and the difference of conformability was not statistically significant (P > 0.05). The mean dose of the whole heart decreased by 23.67% (t = 13.693, P < 0.05) compared with the former. D_max and D_mean of other substructures of the heart were lower than the former. The result of dose verification showed that there was no statistically significant difference in uniformity and conformity between the two planned target doses (P > 0.05). The mean dose of the whole heart of HSH_IMRT was 24.88% (t = 13.782, P < 0.05) lower than that of H_IMRT, and except for the left ventricle and right ventricle, the D_max of other heart substructures and D_mean of all heart substructures decreased. Both the planned and the dose verification result showed that the V₂₀ and the D_mean of the affected lung were lower in HSH_IMRT. Conclusions: Reasonable introduction of MLC shielding technology in H_IMRT can reduce the exposure dose of cardiac and further reduce the risk of radiation damage in heart. (authors)