A Combined Breath Hold and Free Breathing Protocol is Not Feasible for Locoregional Radiation Therapy of Left-Sided Breast Cancer

Deep inspiration breath hold (BH) during irradiation with tangential fields of the left breast has been shown to reduce cardiac dose. For the supraclavicular lymph nodes (LN), however, irradiation during free breathing (FB) may be preferable as BH verification (e.g., by EPID imaging) is cumbersome and limits the use of more complex IMRT. In this study, we explore the possibility of combining BH tangential fields with FB supraclavicular fields. We quantify the amount of displacement of the supraclavicular structures between BH and FB. We retrospectively registered the free breathing CT to the breath hold CT of 13 patients, who were previously treated for (local) left-sided breast cancer in supine position on a breast board. For each patient three rigid body image registrations, translations only, were performed using the following landmarks: 1) EPID skin markers placed on the cranial side of the left breast, 2) the sternal edge of the clavicle denoting the caudal side of the supraclavicular LN, and 3) the acromial edge of the clavicle representative of the cranial border. In this approach landmarks 1 and 2 are indicative of the match line between the fields, while the difference in displacement between marker 2 and 3 represent the variation of motion within the supraclavicular field. All landmarks showed a small displacement in the RL direction (Table 1). The breast marker (1) and sternal end of the clavicle (2) did show a considerable amount of motion in the AP and CC direction (mean displacement of 9 mm and 7 mm, respectively), which was also strongly correlated (R2 = 0.94 and R2 = 0.72 for AP and CC, respectively). The mean displacement of the acromial end of the clavicle (3) was found to be considerably smaller (CC = 2 mm). Further, the difference between the sternal and acromial end of the clavicle was -4.0 mm in the AP direction (range = -14.6 to 0.9 mm), and -4.9 mm (range = -14.2 to 0 mm) in the CC direction. Finally, it is worth noting that the inter-patient variability (Table 1, range of displacements) was large for all landmarks. Due to the large displacement in the CC and AP direction around the match line, we conclude that it is not feasible to combine the irradiation of supraclavicular fields in FB and the tangent fields in BH in locoregional treatment of left-sided breast cancer. The large extent of clavicular motion observed in this study suggests that geometric verification during breath hold is desirable when irradiating the supraclavicular LN with highly conformal IMRT.Scientific Abstract 3692; TableAverage displacement and range between BH-CT and FB-CTRL (mm)AP (mm)CC (mm)1. Breast marker0.0 [-3.6,2.3]10.6 [0.0,22.0]9.0 [2.4,20.3]2. Clavicle sternal end0.0 [-2.6,2.2]6.2 [-1.3,15.2]7.0 [0.4,19.9]3. Clavicle acromial end-0.2 [-3.2,2.0]2.1 [-0.7,6.1]2.0 [-6.8,13.6] Open table in a new tab