Whole Breast Irradiation with Halcyon™ 2.0: Workflow and Efficiency of Field-in-Field Treatment with Dynamic Beam Flattening Technique and kV Cone Beam Computed Tomography.

Whole breast irradiation accounts for a substantial fraction of patients treated in Radiation Oncology clinics. The recently introduced Halcyon™ platform provided a high-throughput, simplified workflow. The 2.0 version introduced new features such as the dynamic beam flattening (DBF) technique that uses the upper layer of the multi-leaf collimator (MLC) to create a flat beam profile at depth and an improved kV cone beam computed tomography (kV CBCT). In this case report, we described our experience in whole breast irradiation with Halcyon 2.0 new features. The patient was simulated in the supine position with the same immobilization technique used on C-arm linacs and an additional contralateral elbow position measurement to ensure clearance. The treatment planning process using DBF and field-in-field technique was similar to the traditional flattened beam planning and did not require additional training. Dosimetric analysis showed satisfactory dose-volume histogram (DVH) parameters that met all the planning objectives, with maximal dose at 107% and V105% at 3.6% of the breast volume. Daily image-guided radiation therapy (IGRT) using improved CBCT showed excellent soft tissue contrasts and sufficient field of view. The average imaging and treatment time was nine minutes, and the average in-room time was 16.2 minutes. These treatment times were substantially higher than those for breast treatments on our Halcyon platform using an irregular surface compensator technique. The use of DBF contributed to the majority of treatment time increase due to the motion of the upper layer of the MLC to create a flat beam profile. The total treatment time using DBF might be too long for patients with deep inhalation breast hold (DIBH) and can be drastically reduced using an irregular surface compensator technique, also known as the electronic tissue compensation (ECOMP) technique, instead of the DBF-enabled field-in-field technique.