(P008) Prospective Assessment of Simulated Prone Whole-Breast Radiation Therapy vs Supine Whole-Breast Radiation Therapy With Respiratory Gating: Significant Lung Dose Reduction With Prone Positioning

Samuel M. Richter, MD, Katrina Stellingwerf, CMD, Dwaine Spence, CMD, Kiernan May, CMD, Alexander Banashkevich, MD, Anna Shapiro, MD; SUNY Upstate Medical University

PURPOSE: To prospectively evaluate which of the two most common radiation therapy (RT) techniques best spares organs at risk (OARs) for left-sided breast cancer patients undergoing adjuvant whole-breast RT (WBRT) as part of their breast-conserving treatment.

METHODS: Twenty-five consecutive, node-negative, Tis–T2N0 left-sided breast cancer patients who were candidates for WBRT following lumpectomy were enrolled in this prospective trial. Each patient underwent CT simulation for planning in the supine position with four-dimensional (4D) CT simulation using the Varian Real-Time Position Management respiratory gating system and in the prone position. Respiratory phases in which the heart was maximally displaced from the chest wall were selected as the optimum supine positioning, and a maximum intensity projection (MIP) file was created for treatment planning. If there was no significant cardiac motion, planning was performed with the all-phase MIP set. For each dataset, OARs were identified. Treatment planning utilizing the two CT studies was performed with conformal tangential fields, utilizing a forward-planning field-in-field technique. Dosimetric analysis of each patient’s best supine plan vs her own prone plan was performed.

RESULTS: Twenty-one patients were eligible for plan analysis. Median age was 59 years (range: 28–75 yr). In all patients, the prone position had resulted in significant reductions in lung V5 (P < .0001), V10 (P < .0001), and V20 (P < .0001) compared with best supine positioning. The lung V20 was reduced by 11.66% in the prone position. Evaluated separately, the seven patients (33.3%) whose best supine position incorporated respiratory gating continued to demonstrate a significant reduction in dose to the lung in the prone position.

CONCLUSION: While respiratory-gated RT can reduce the dosimetric parameters for lungs and heart compared with non-gated ER, the results of this study demonstrated a marked further reduction in pulmonary doses for tangentially treated left-sided breast cancer patients, without compromising target coverage.

Proceedings of the 98^th Annual Meeting of the American Radium Society - americanradiumsociety.org