Evaluation of Cardiac Dose Reduction With Deep Inspiration Breath Hold in Patients With Left-Sided Breast Cancer Receiving Adjuvant Radiation Therapy

Abstract

Studies have suggested increased cardiac morbidity from radiation exposure to the heart and left anterior descending artery (LAD) in breast cancer patients receiving adjuvant radiation therapy (RT). Threshold dose limits to these structures have not yet been determined. More recent international clinical trial protocols have proposed a mean heart dose constraint of < 4 Gy. No dose limits have been clearly delineated for the LAD. Deep inspiration breath hold (DIBH) techniques have demonstrated reduction in heart, LAD, and lung dose for treatment of left-sided breast cancers. There is limited data on which patients derive most benefit from DIBH technique and if this technique is required to meet the mean heart dose constraint of < 4 Gy. Our primary objective was to compare reduction in cardiac and LAD doses in left-sided breast cancer patients undergoing adjuvant RT with DIBH versus the standard free-breathing (FB) method to determine which patients derive the most benefit. The secondary objective was to determine if DIBH technique is required to meet the heart dose constraint of < 4 Gy. Twenty consecutive patients with left-sided breast cancer underwent CT simulation scan in FB and DIBH. Patients were grouped into two cohorts: those receiving whole breast irradiation alone +/- a boost (WBRT) versus those receiving whole breast/chest wall irradiation with regional nodal irradiation (WBRT + RNI). 3D conformal plans were devised, and dosimetric comparisons for the heart and LAD were made between the two techniques for each cohort. Eleven patients received WBRT while nine patients received WBRT + RNI. All patients had comparable CTV coverage on both DIBH and FB treatment plans. Mean heart and LAD artery doses were lower in all DIBH versus FB plans, but the benefit was larger in the group receiving RNI compared to those receiving WBRT alone (mean relative reduction in mean heart and LAD dose: 55.9% and 71.9% vs 34.2% and 45.1%, respectively). All patients met the mean heart dose constraint of < 4 Gy on DIBH. On FB, only 1 patient in the WBRT group did not meet this constraint, compared to 5 patients in the WBRT +RNI group. Patients receiving WBRT+RNI had a greater reduction in heart and LAD dose from DIBH than patients receiving WBRT alone. The majority of patients receiving WBRT met a mean heart dose of < 4 Gy on FB planning, while less than half of patients receiving WBRT + RNI were able to meet this constraint. These findings suggest a greater benefit from DIBH treatment in patients receiving RNI, while patients receiving WBRT alone may be safely treated with a FB technique. Ongoing prospective cohorts are being evaluated to ensure validity of these findings.