SU‐F‐J‐22: Lung VolumeVariability Assessed by Bh‐CBCT in 3D Surface Image Guided Deep InspirationBreath Hold (DIBH) Radiotherapy for Left‐Sided Breast Cancer

Abstract

Purpose:With the increasing use of DIBH techniques for left‐sided breast cancer, 3D surface‐image guided DIBH techniques have improved patient setup and facilitated DIBH radiation delivery. However, quantification of the daily separation between the heart and left breast still presents a challenge. One method of assuring separation is to ensure consistent left lung filling. With this in mind, the aim of this study is to retrospectively quantify left lung volume from weekly breath hold‐CBCTs (bh‐CBCT) of left‐sided breast patients treated using a 3D surface imaging system.Methods:Ten patients (n=10) previously treated to the left breast using the C‐Rad CatalystHD system (C‐RAD AG, Uppsala Sweden) were evaluated. Patients were positioned with CatalystHD and with bh‐CBCT. bh‐CBCTs were acquired at the validation date, first day of treatment and at subsequent weekly intervals. Total treatment courses spanned from 3 to 5 weeks. bh‐CBCT images were exported to VelocityAI and the left lung volume was segmented. Volumes were recorded and analyzed.Results:A total of 41 bh‐CBCTs were contoured in VelocityAI for the 10 patients. The mean left lung volume for all patients was 1657±295cc based on validation bh‐CBCT. With the subsequent lung volumes normalized to the validation lung volume, the mean relative ratios for all patients were 1.02±0.11, 0.97±0.14, 0.98±0.11, 1.02±0.01, and 0.96±0.02 for week 1, 2, 3, 4, and 5, respectively. Overall, the mean left lung volume change was ≤4.0% over a 5‐week course; however left lung volume variations of up to 28% were noted in a select patient.Conclusion:With the use of the C‐RAD CatalystHD system, the mean lung volume variability over a 5‐week course of DIBH treatments was ≤4.0%. By minimizing left lung volume variability, heart to left breast separation maybe more consistently maintained.AN Gutierrez has a research grant from C‐RAD AG.