TU‐F‐17A‐06: Motion Stability and Dosimetric Impact of Spirometer‐Based DIBH‐RT of Left‐Sided Breast Cancer

Abstract

Purpose:Patients undergoing radiotherapy (RT) for left‐sided breast cancer have increased risk of coronary artery disease. Deep Inhalation Breath Hold assisted RT (DIBH‐RT) is shown to increase the geometric separation of the target area and heart, reducing cardiac radiation dose. The purposes of this study are to use Cine MV portal images to determine the stability of spirometer‐guided DIBH‐RT and examine the dosimetric cardiopulmonary impact of this technique.Methods:Twenty consecutive patients with left‐sided breast cancer were recruited to the IRB‐approved study. Free‐breathing (FB) and DIBH‐CT's were acquired at simulation. Rigid registration of the FB‐CT and DIBH‐CT was performed using primarily breast tissue. Treatment plans were created for each FB‐CT and DIBH‐CT using identical paired tangent fields with field‐in‐field or electronic compensation techniques. Dosimetric evaluation included mean and maximum (Dmax) doses for the left anterior descending artery (LAD), mean heart dose, and left lung V20. Cine MV portal images were acquired for medial and lateral fields during treatment. Analysis of Cine images involved chest wall segmentation using an algorithm developed in‐house. Intra‐ and inter‐fractional chest wall motion were determined through affine registration to the first frame of each Cine.Results:Dose to each cardiac structure evaluated was significantly (p<0.001) reduced with the DIBH plans. Mean heart dose decreased from 2.9(0.9–6.6) to 1.6(0.6–5.3) Gy; mean LAD dose from 16.6(3–43.6) to 7.4(1.7–32.7) Gy; and LAD Dmax from 35.4 (6.1–53) to 18.4(2.5–51.2) Gy. No statistically significant reduction was found for the left lung V20. Average AP and SI median chest wall motion (intrafractional) was 0.1 (SD=0.9) and 0.5 (SD=1.1) mm, respectively. Average AP inter‐fractional chest wall motion was 2.0 (SD=1.4) mm.Conclusion:Spirometer‐based DIBH treatments of the left breast are reproducible both inter‐ and intra‐fractionally, and provide a statistically and potentially clinically useful dosimetric advantage to cardiac structures.