(P017) Dosimetric Evaluation of Respiratory-Gated Radiotherapy for Left-Sided Breast Cancer

Veronica Finnegan, MD, Varun Chowdhry, MD, Weidong Li, PhD, Katrina Stellingworth, CMD, Jeffrey Bogart, MD, Anna Shapiro, MD; SUNY Upstate; Massachusetts General Hospital

PURPOSE/OBJECTIVES: Adjuvant radiotherapy is associated with improvements in local control and survival in patients with breast cancer. As oncological outcomes have improved, there is a greater importance in preventing long-term toxicity from treatment. Technological advancements in radiotherapy delivery have the potential to allow better coverage of complex targets while reducing doses to normal structures. The use of four-dimensional computed tomography (4DCT) and respiratory gating has increased in clinical practice, but there is limited information regarding the utility of respiratory gating in breast cancer. The purpose of the study is to assess the dosimetric benefits of respiratory gating for patients receiving radiotherapy for left-sided breast cancer.

PATIENTS/METHODS: A total of 38 women with left-sided breast cancer were treated with respiratory gating between 2009 and 2013. All patients underwent 4DCT simulation using the Varian Real-Time Position Management respiratory gating system. The determination to use respiratory gating was at the discretion of the treating physician. For this study, maximum intensity projection (MIP) image sets containing images from all phases were also created. The original plans were copied to both the gated MIP and the all-phase MIP sets for dosimetric evaluations. Dose-volume histograms were calculated and compared. Doses to predefined heart and lung parameters were compared on two plans for each patient. Cardiac and pulmonary doses were compared for each patient using a two-sided paired difference test (t-test).

RESULTS: The use of respiratory gating resulted in statistically significant dose reductions to the heart on nearly all parameters evaluated. Mean whole heart dose was 368 cGy with gating and 389 cGy without gating (P < .001). V5 heart was 77% with gating and 84% without gating (P < .001). Max left anterior descending (LAD) dose was 3,990 cGy with gating and 4,264 cGy without gating (P = .009), and mean left ventricular dose was 511 cGy with gating and 549 cGy without gating (P < .001). There were trends toward a reduction of mean LAD dose (2,298 cGy with gating and 2,569 cGy without gating; P = .059) and max left ventricular dose (4,021 cGy with gating and 4,183 cGy without gating; P = .067). Statistically significant differences were not noted in any of the lung parameters tested (V5, V20, or V40).

CONCLUSION: The use of respiratory gating has resulted in small but statistically significant reductions in heart dose. Further studies are needed to understand the clinical implications of these differences.

Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org