Dosimetric Correlation Between The Depth of Chest Wall Expansion and Heart Dose in Left Breast Cancer Irradiation Using Deep Inspiratory Breath Hold Technique

Introduction and Objective: In adjuvant radiotherapy for left breast cancer, a significant heart volume may be included in the radiation field leading to long-term cardiac toxicities. Deep inspiratory breath hold technique (DIBH) leads to chest wall separation away from the heart and thus can reduce the heart dose compared to free breathing technique. The aim of this study is to correlate dosimetrically the degree of chest wall expansion measured on planning 4D-CT scan to the heart dose in left breast cancer irradiation using DIBH technique. Materials and Methods: Thirty four patients with left breast cancer planned for adjuvant radiotherapy were included. All patients were scanned by Varian RPM (Real Time Position Managment) respiratory gating system using infrared reflecting markers and a video camera to detect the respiratory motion. IMRT or VMAT plans were done for all patients with a prescribed dose 50Gy/25fr/5w with or without operative bed boost dose 10Gy/5fr/1w. The degree of chest wall expansion was identified by measuring the amplitude of DIBH breathing curve from baseline in planning 4D-CT scan in centimeters. The depth of expansion was correlated dosimetrically with the heart V20, V30, and mean heartdose. Results: The mean distance of chest wall expansion was 2.9cm. The mean left lung dose was 8.6Gy. The mean left lung V20 was 13.8%. The mean heart dose was 1.8Gy. The mean heart V30 was 0.6%. A statistically significant reduction of the mean heart dose and V30 was observed with chest wall expansion of 1.4cm or higher (p<0.05). Conclusion: In DIBH technique, the depth of chest wall expansion in 4DCT planning is dosimetrically correlated with the cardiac dose reduction during adjuvant irradiation of left breast cancer. Further clinical studies are needed to translate this dosimetric advantage into clinical benefit.