Abstract
We quantify dosimetric differences between 3-dimensional (3D) planning and volumetric modulated arc therapy (VMAT) in breast cancer patients requiring comprehensive regional nodal irradiation (CRNI). Target volume dose, prescription isodose conformality to target volumes, plan hotspots, normal tissue dose-volume metrics, and back and shoulder dose were compared for VMAT and 3D plans of 50 patients. Metrics used to compare VMAT plans with 3D plans included the percentage of primary clinical target volumes (CTVs) receiving 98% of a prescription dose of 5000 cGy, CTV dose hotspots, the extra treatment volume (ETV), and the portion of the patient's body receiving 90% of the CTV prescription dose (excluding the primary target volume). Superior values for these metrics were found for VMAT plans when compared to 3D plans. The mean percentage of the target volume receiving 98% of the prescription dose of 3D plans was 95.4% versus 98.9% among VMAT plans (P < .01). The mean target volume hotspot of 3D plans was 7200 cGy versus 5450 cGy for VMAT plans (P < .01). A mean ETV found for 3D plans was nearly double that found among VMAT plans (5.3% vs 2.7%, P < .01). VMAT plans resulted in lower doses to the shoulder and back. Mean total body volumes of VMAT plans were lower for dose thresholds of 100% to 130% of the prescription. VMAT plans generally had superior values for institutional normal tissue dose constraints. VMAT is superior to 3D planning across multiple metrics for breast cancer patients requiring CRNI. Insurance coverage for VMAT should not require 3D comparison plans.