SU‐E‐T‐609: Impact of Breath‐Hold Level, Age, and BMI on Normal Tissue Dosimetry for Left Breast Cancer Patients

Purpose: This study evaluates dose to heart, left anterior descending coronary artery (LAD) and left lung as a function of breath-hold level, age and body mass index (BMI), for patients undergoing deep-inspiration breath-hold (DIBH) treatments for left breast cancer. Methods: The study involved 35 patients with free-breathing and breath-hold CT scans. The RPM System (Varian Oncology Systems, Palo Alto, Ca) was used to measure breath-hold level which is defined as the distance from end of normal inspiration to the average breath-hold level during simulation. RPM data was analyzed. Free-breathing and breath-hold scans were fused by matching the field borders, scar, excision cavity, and skin. All image fusions and contours were performed by one physician. Dose change was expressed as percent change from free-breathing to breath-hold. Mean doses to heart and LAD and V20 of the left lung were analyzed. Clinical parameters evaluated were breath-hold level, patient age and BMI. Results: Using breath-hold technique an average mean dose reduction was noted to heart and LAD of 61% and 69%, respectively. Average left lung V20 for free-breathing and breath-hold were 18% and 13%, respectively. Mean heart dose reduction correlated with both breath-hold level (r = 0.50) and age (r = 0.55). Fair correlation was noted for LAD mean dose reduction and breath-hold level (r = 0.47), but little correlation was found for BMI or age. Little or no correlation was found between average left lung V20 change and breath-hold level, BMI or age. Conclusions: On average, all patients experienced a dose reduction to heart and LAD with breath-hold. Good correlations were noted in mean heart dose reduction with breath-hold level and age. This study indicates younger patients treated with breath-hold typically achieved greater heart dose reduction and those with higher breath- hold levels demonstrated larger dose reduction to heart and LAD.