EFFECT OF BREAST VOLUME ON TREATMENT REPRODUCIBILITY ON A TOMOTHERAPY UNIT IN THE TREATMENT OF BREAST CANCER

Purpose: To determine whether the volume of a patient's breast is correlated with reliable daily setup in treatment cif breast cancer with a helical tomotherapy treatment unit. Methods and Materials: Thirty-six consecutive patients with breast cancer were treated on a helical tomotherapy unit. During simulation, kilovoltage CT images were obtained for treatment planning. These were fused with daily megavoltage CT scans, and after setup based on skin marks and laser alignment the necessary shifts were carried out. The magnitude of daily shifts (in millimeters) was retrospectively obtained from the daily image fusions, and the breast volume was obtained from the treatment plan. A total of 873 fusion scans were reviewed. Random error for absolute and directional daily shifts was evaluated for correlation to volume. Variation over time was also evaluated. Results: Mean (SD) random shift for all patients in the lateral, longitudinal, and vertical directions was 2.7 (2.0), 3.1 (1.5), and 3.2 (2.6) mm, respectively. Mean (SD) absolute distance shifted was 6.0 (3.5) mm. There was no significant correlation between mean absolute or mean directional daily shift and breast volume (0.08, 0.08, 0.22, and 0.07, respectively). There was no correlation between setup variation and time. Conclusions: In this cohort, there was no correlation between breast volume and degree of daily shift. There was no correlation between time course and setup variation. Therefore, setup variation does not improve or degrade with repeated treatment setups. (C) 2011 Elsevier Inc.