LAUSR

Background and Aims: While bilateral breast cancer is rare, the challenge for the radiation oncologist is to limit the dose to multiple important organs-at-risk and reducing the chance of overlapping tangential fields to limit hotspots. In this study, we present a simple technique to verify the setup accuracy of breast tangential fields using the electronic portal imaging device (EPID) for bilateral breast cancer. Patients and Methods: A 74-year-old female, with bilateral breast cancers, right staged as T1N0M0 and the left T2N1M0, received postoperative radiotherapy following bilateral breast conservative surgery. Standard CT-based simulation and target delineation were done, followed by treatment planning using classical field arrangements with two separate isocenters, one for each breast (keeping identical anteroposterior and superior-inferior coordinates). The planned doses were 45 Gy/25 # for whole breasts, plus tumor bed boost of 15 Gy/6 # and 50 Gy/25 # to left supraclavicular fossa. After setting up the patient, two small lead wires were placed at the medial borders of medial tangents (as seen on light fields) of each breast (longer one for left), followed by EPID imaging (dual exposure: One lateral tangent field image and other larger to include lead wires) of respective contralateral lateral tangential fields to verify that there was no actual overlapping with the opposite medial tangential field, as indicated by the lead wires. Conclusion: The study has validated a simple EPID-based technique for routine use in the field matching for radiotherapy of bilateral breast cancer.