Chest dose assessment in breast cancer therapy using two electron energies

Background: Electron therapy has advantages of dose uniformity in target volume and dose reduction in deeper tissues for breast cancer therapy. The aim of this study was to determine observed dose in target volume and normal tissues such as lung in breast cancer therapy after mastectomy. Methods: The phantom was designed based on the chest wall computed tomography (CT) images after mastectomy and treatment planning software. Two linear accelerator (Neptune 10 and Saturn 20) machines were used to deliver electron beams at a dose of 200 cGy (10 and 13 MeV). Dose measurements were done using thermoluminescence dosimeter lithium fluoride chips (TLD-100: LiF: Mg; Tl). Findings: The percentage of measured dose in internal mammary nodes, axillary nodes, and chest wall using 13 MeV was found to be 97.5, 96, and 98, respectively. In treatment with 10 MeV electron, this values changed to 99.7, 90.5, and 77 percent, respectively. The anterior lung percentage dose was 78 with 13 MeV electrons while the posterior part of lung received 47 percent with 10 MeV electron beam. Dose values for anterior and posterior part of lung changed to 83 and 45 percent, respectively. Conclusion: Using 13 MeV, internal mammary and axillary lymph nodes as well as the chest wall received adequate doses but lung received excessive dose. Using 10 MeV, internal mammary nodes and chest wall were well exposed to radiation, but axillary lymph nodes did not receive enough dose. Therefore, this dose shortage should be compensated by additional posterior fields using radiation therapy with photon energies. © 2017, Isfahan University of Medical Sciences(IUMS). All rights reserved