A Potential Pitfall and Clinical Solutions in Surface-Guided Deep Inspiration Breath Hold Radiation Therapy for Left-Sided Breast Cancer

Purpose: Deep inspiration breath hold (DIBH) is an effective technique to spare the heart in treating left-sided breast cancer. Surface guided radiation therapy (SGRT) is increasingly applied in DIBH setup and motion monitoring. Patient-specific breathing behavior, either thoracically driven or abdominally driven (A-DIBH), should be unaltered, online identified, and monitored accordingly to ensure reproducible heart -sparing treatment. Methods and Materials: Sixty patients with left-sided breast cancer treated with SGRT were analyzed: 20 A-DIBH patients with vertical chest elevation (VCE <= 5 mm) were prospectively identified, and 40 control patients were retrospectively and randomly selected for comparison. At simulation, both free -breathing (FB) and DIBH computed tomography (CT) were acquired, guided by a motion surrogate placed around the xiphoid process. For SGRT treatment setups, the region of interest (ROI) was defined on the CT chest surface, and the surrogate-based setup was a backup. For all 60 patients, the VCE was measured as the average of the FB-toDIBH elevations at the breast and xiphoid process, together with abdominal elevation. In the 40 -patient control group, A-DIBH patients (VCE < 5 mm) were identified. Of the 20 A-DIBH patients, 10 were treated with volumetric modulated arc therapy plans, and 10 patients were treated with tangent plans. Clinical DIBH plans were recalculated on FB CT to compare maximum dose (D-max), 5% of the maximum dose (D-5%), mean dose (D-mean), and V-3oGy, V-2oGy, and V-5Gy of the heart and lungs and their significance. Results: In the 20 A-DIBH patients, VCE = 3 +/- 2 mm, surrogate motion (9 +/- 6 mm), and abdomen motion of 14 +/- 5 mm are found. Heart dose reduction from FB to DIBH is significant (P <.01): Delta D-max = -8.4 +/- 9.8 Gy, Delta D-5%= -2.4 +/- 4.4 Gy, and Delta D-mean = -0.6 +/- 0.9 Gy. Six out of 40 control patients (15%) are found to have VCE <= 5 mm. Conclusions: A-DIBH (VCE <= 5 mm) patient population is significant (15%), and they should be identified in the SGRT workflow and monitored accordingly. A new abdominal ROI or an abdominal surrogate should be used instead of the conventional chest -only ROI. Patient -specific DIBH should be preserved for higher reproducibility to ensure heart sparing.