MR image-guided radiation therapy (MR-IGRT) for external beam accelerated partial breast irradiation (APBI): Evaluation of delivered dose and intra-fractional cavity motion

Publication date: Available online 20 August 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Sahaja Acharya, Benjamin W. Fischer-Valuck, Thomas Mazur, Austen Curcuru, Karl Sona, Rojano Kashani, Olga Green, Laura Ochoa, Sasa Mutic, Imran Zoberi, H. Harold Li, Maria A. Thomas
Purpose/Objective: To utilize MR-image guided radiation therapy (MR-IGRT) for accelerated partial breast irradiation (APBI) to: (1) determine intra-fractional motion of the breast surgical cavity and (2) assess delivered dose versus planned dose.Materials/MethodsThirty women with breast cancer (Stages 0-I) who underwent breast conserving surgery were enrolled in a prospective registry evaluating APBI using a 0.35 T MR-IGRT system. CTV was defined as the surgical cavity plus a 1 cm margin (excluding chest wall, pectoral muscles, and 5 mm from skin). No additional margin was added for PTV. A volumetric MRI was acquired prior to each fraction and patients were setup to the surgical cavity as visualized on MRI. To determine the delivered dose for each fraction, the electron density map and contours from the CT simulation were transferred to the pre-treatment MRI via rigid registration. Intra-fractional motion of the surgical cavity was determined by applying a tracking algorithm to the cavity contour as visualized on cine MR.ResultsMedian PTV volume was reduced by 52% when utilizing no PTV margin compared to a 1 cm PTV margin used conventionally. The mean difference between planned and delivered dose to the PTV (V95) was 0.6% ± 0.1%. The mean cavity displacement in the anterior-posterior (AP) and superior-inferior (SI) directions was 0.6 ± 0.4 mm and 0.6 ± 0.3 mm, respectively. The mean margin required for at least 90% of the cavity to be contained by the margin for 90% of the time was 0.7 mm (5^th-95^th percentile: 0-2.7 mm).ConclusionMinimal intra-fractional motion was observed and the mean difference between planned and delivered dose was less than 1%. Assessment of efficacy and cosmesis of this MR-guided APBI approach is underway.

Teaser

We utilize MR-image guided radiation therapy (MR-IGRT) for accelerated partial breast irradiation (APBI) to: (1) determine intra-fractional motion of the breast surgical cavity and (2) assess delivered dose versus planned dose. Our results indicate there is minimal intrafractional motion and there is good agreement between delivered and planned dose. Assessment of efficacy and cosmesis of this MR-guided APBI approach is underway.


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