Feasibility of Preoperative Single Fraction Partial Breast Radiotherapy for Early Stage Breast Cancer.

Abstract

Abstract Introduction: Preliminary data supports the efficacy of partial breast irradiation (PBI) in carefully selected patients. However, in 2008, several series evaluating external beam PBI reported negative toxicity outcomes, possibly related to large volumes of normal tissue receiving near-prescription doses.We hypothesized that delivery of external beam PBI in a single fraction to the preoperative tumor volume, as defined by magnetic resonance imaging (MRI), would be dosimetrically feasible and result in decreased dose to the ipsilateral breast as compared to institutional historical controls.Methods: Ten patients with unifocal T1 breast cancer who had undergone a preoperative MRI were identified. Contrast-enhanced subtraction MR images were loaded into Eclipse treatment planning software and used to define the gross tumor volume (GTV). A 1.5cm uniform expansion (minus first 5mm of skin) was used to generate the clinical target volume (CTV) for dose-volume analysis. An additional 2-3 mm margin was included for penumbra.The first 3mm of skin/subcutaneous tissue was defined as an avoidance structure. Bilateral lungs and heart were segmented. A prospective “virtual plan” was created using four photon beams in a non-coplanar beam arrangement and optimized to deliver 15Gray (Gy) to the CTV.Specific dosimetric data was extracted including dose conformity (breast volume receiving 100% of the dose/CTV) and dose to the ipsilateral breast, ipsilateral lung, and heart.Results: The median breast volume was 1713cc's (range 1014 – 2140cc's) and the median target volume only 41cc's (26-62cc's). In all cases, 95% of the prescription dose covered 100% of the CTV volume. Median dose conformity was 1.2 (range 1.1-1.6). Maximum dose for all plans was not greater than 110%. Doses to the heart and lung were negligible.Median maximum skin dose was 9.3Gy or 62% of the prescription dose. Median maximum dose to 1cc of skin was reduced to 7.0Gy and at 10cc's skin volume, the median maximum was only 4.9Gy.Median percent of the ipsilateral breast volume receiving 100% of the dose (V100) was only 3.5% (range 2.4-4.7%). The median percent volume receiving 50% of the dose (V50) was 13% (range 7.5-20.8%), substantially less than institutional experience with post-operative PBI. Pre-operative PBIPost-operative PBI n=10n=27 Median (range)Median (range)V1003.5% (2.4-4.7)20% (3-42)V5013% (7.5-20.8)43% (24-65) Conclusion: Pre-operative radiotherapy is dosimetrically feasible in women with small breast tumors. Excellent target coverage with negligible dose to normal tissue can be achieved. Skin dose appears reasonable given the small volumes.Median V100 and V50 compare favorably to institutional experience with post-operative PBI. A prospective Phase I trial evaluating this technique is undergoing institutional review. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4105.