[P277] Investigation of mean heart dose reduction inter-fraction variation in left-sided breast cancer radiotherapy using active breath coordinator moderate deep inspiration breath hold

Abstract

Purpose Left-sided breast radiotherapy is associated with increased risk of coronary artery disease. Active Breathing Coordinator (ABC) reduces radiation dose to the heart and preserves local control in patients with left breast cancer. The aim of this study is to estimate the dose reduction to the heart and its inter-fraction variation in moderate deep inspiration breath hold (mDIBH) breast radiotherapy using ABC (Elekta). Methods Ten patients with left-sided breast cancer with tangential radiotherapy plans and ten patients with VMAT plans performed using to Monaco (Elekta) TPS, where included in the study. All the patients were trained on ABC procedure to enhance patient compliance and to determine individual (mDIBH) levels, which was set at 70–80% of maximum inspiratory capacity. During simulation two sets of CT images were acquired for each patient, one with mDIBH with ABC system and the other with free breathing. Treatment plans were performed for both scans and the mean dose to the heart was recorded. Treatment was performed using the ABC system. 200 cone-beam CT (CBCT) scans were acquired for all patients investigated throughout their course of treatment to take into account inter-fraction patient set-up inaccuracies. CBCTs were exported to Monaco TPS for registration and mean heart dose determination after the application of the original patient plan. Results For all patients evaluated, compared to free breathing, mDIBH with ABC significantly reduced mean dose to the heart by 20% or greater independently of the planning technique (tangential fields or VMAT). This reduction remains the same with minor differences (on average 1 cGy per fraction) throughout the treatment course. Conclusion Moderate deep inspiration breath hold (mDIBH) breast radiotherapy using ABC (Elekta) can significantly reduce mean dose to the heart. Variation in mean heart dose was minor and mean dose remains significantly reduced throughout the treatment course without being affected by inter-fraction variations.