Critical Evaluation of Secondary Cancer Risk After Breast Radiation Therapy with Hybrid Radiotherapy Techniques.

Background: As hybrid radiotherapy technique can effectively balance dose distribution between targets and organs, it is necessary to evaluate the late effects related to radiotherapy. The aim of the study was to calculate and provide individual estimates of the risks for hybrid radiotherapy techniques in breast cancer patients.

Methods: Whole-breast irradiation was performed in 43 breast cancer patients by using 3D conformal, intensity-modulated and hybrid techniques. The excess absolute risk (EAR), lifetime attributable risk (LAR) and normal tissue complication probability (NTCP) were calculated to estimate risks in organs. The risk variability in contralateral breast was assessed by using the patient's anatomic parameters.

Results: Compared with IMRT and FinF, hybrid techniques achieved satisfactory dose distribution and comparable or lower estimated risks in organs. The LAR was estimated to be up to 0.549% for contralateral lung with advantages of tangential techniques over H-VMAT. For ipsilateral lung, the LAR was estimated to be up to 9.021%, but lower in H-VMAT and FinF without significant difference. The risk of thyroid was negligible in overall estimation. For contralateral breast, the LAR was estimated to be up to 0.865% with advantages of MH-IMRT and H-VMAT over TF-IMRT. The fraction of individual variability could be explained by using anatomic parameters of minimum breast distance (MBD) and minimum target concave angle (θ_MTCA). NTCP for all analyzed endpoints was significantly higher in TF-IMRT relative to FinF and hybrid techniques, while TH-IMRT and H-VMAT were presenting lower toxicity risk. However, MH-IMRT presented a higher probability of toxicity in lung. For most cases, H-VMAT demonstrated a benefit for contralateral breast, heart and lung sparing.

Conclusion: The optimal treatment should be performed individually according to anatomic parameters and balances between EAR and NTCP. Individual assessment may assist in achieving optimal balances between targets and organs as well as supporting clinical decision-making processes.