RPM inspiration gating: Improving radiotherapy for left breast cancer patients with anterior heart position

Background: Adjuvant radiotherapy for breast cancer reduces local recurrence and improves survival. In patients with left sided breast cancer, anterior heart position or medial tumor location may cause inadequate breast coverage due to heart shielding. Respiration gating using the Real-time Position Management (RPM) system enables pushing the heart away from the tangential fields during inspiration, thus optimizing the treatment plan. Objectives: To compare breathing inspiration gating (IG) techniques with free breathing (FB), focusing on breast coverage. Methods: The study comprised 49 consecutive patients with left sided breast cancer who underwent lumpectomy and adjuvant radiation. RPM was chosen due to insufficient breast coverage caused by an anterior heart position or medial lumpectomy cavity. FB and IG computed tomography simulations were generated for each patient. Breast (PTVbreast) and lumpectomy cavity (CTVlump) were defined as the target areas. Optimized treatment plans were created for each scan. A dosimetric comparison was made for breast coverage and heart and lungs doses. Results: PTVbreast V95% and mean dose (Dmean) were higher with IG vs. FB (82.36% vs. 78.88%, P = 0.002; 95.73% vs. 93.63%, P < 0.001, respectively). CTVlump V95% and Dmean were higher with IG (98.87% vs. 88.92%, P = 0.001; 99.14% vs. 96.73%, P = 0.003, respectively). The cardiac dose was lower with IG. The IG left lung Dmean was higher. No statistical difference was found for left lung V20. Conclusions: In patients with suboptimal treatment plans due to anterior heart position or medial lumpectomy cavity, RPM IG enabled better breast/tumor bed coverage and reduced cardiac doses.