Author: Xiu tong Lin 👨🔬
Affiliation: Department of Radiation physics and technology, Shandong Second Provincial General Hospital 🌍
Purpose: To compare the dosimetric differences between the photon and proton plans and between the different target according to the placement of the implants for patients undergoing radiotherapy after implant-based reconstruction of breast cancer.
Methods: Fifteen early-stage left-breast cancer patients who underwent post-mastectomy radiotherapy with implants placed posterior to the pectoralis muscle were conducted. The initial target did not include the implant and the posterior chest wall. New targets were delineated to simulate the target with implants placed anterior to the pectoralis muscle, including the skin, subcutaneous tissue, implant, and pectoralis muscle. Five treatment plans were designed for each target: IMRT and VMAT plans based on a single-layer MLC accelerator (Varian Trilogy) and a dual-layer orthogonal MLC accelerator (Linatech VenusX), and intensity-modulated proton (IMPT) plans (Varian ProBeam). Dosimetric differences between the 10 plans were compared.
Results: Proton plans significantly improved the coverage and uniformity of target compared with photon plans. The two proton plans reduced the doses of all OARs compared to photon plans, with a significant reduction in doses to the heart, left ventricle (LV), and left anterior descending artery (LAD). VenusX plans significantly reduced the high-dose areas (V20, V30, V40) and mean doses to the left lung and heart, as well as the mean, maximum doses, and V40 of the LV and LAD, compared to Trilogy plans. Plans of implants placed posterior to the pectoralis muscle significantly reduced the doses to the lungs, heart and substructures compared to plans of implants placed anterior to the pectoralis muscle.
Conclusion: For post-mastectomy radiotherapy in left-breast cancer patients with implant reconstruction, proton plans significantly reduce the doses to organs at risk, regardless of the placement of the implant. The surgical method of placing implants posterior to the pectoralis muscle shows a more optimal dose distribution.