MRI-Guided Radiation Therapy Modernizes Breast Conservation Methods

Bethany Anderson, MD

Assistant Professor

University of Wisconsin Carbone Cancer Center

Additionally, the European Organization for Research and Treatment of Cancer (EORTC) study, a randomized trial assigning women to receive whole breast radiation therapy with or without a lumpectomy cavity boost, has shown that the lumpectomy boost further reduces IBTR risk, from 16.4% to 12.0% at 20 years.² This study also found that the lumpectomy cavity boost increased the risk for severe fibrosis from 1.8% to 5.2% at 20 years. Several factors correlated with cosmetic outcome, including the excision volume and radiation-dose homogeneity.³

The technique used to identify and boost the lumpectomy cavity on the EORTC study was variable. Patients receiving an external beam radiation boost were treated with electrons or photons, using the relatively simple technologies that were state of the art at the time that the study was conducted (from 1989 to 1996). A total of 3 transverse CT sections were obtained through the breast, including 1 aimed at the center of the surgical bed, and radiation dose was prescribed to a single point on that central section.

Clearly, this technique did reduce IBTR risk, as shown by the EORTC research group. However, the planning method was based upon fairly limited knowledge of where the surgical bed was actually located within the breast. If a benefit can be demonstrated with a technique that likely missed a portion of the surgical bed in some cases, how much more efficacious might we be with highly accurate radiotherapy targeting?

Fast forward to 2016, when women routinely undergo treatment planning CT scans to accurately identify all postsurgical changes and clips within the breast tissue. This greatly assists with target delineation, such that a homogeneous radiation plan can be designed to encompass the entirety of the surgical bed.

New System Tested

Most commonly, however, daily target localization is done using surrogates for the lumpectomy cavity, such as skin tattoos, bony anatomy (ie, ribs identified using x-rays, Figure A), and the location of the skin incision.At the University of Wisconsin, women currently have the option to participate in a prospective study wherein their lumpectomy cavity boost is delivered on a novel MRI-guided radiotherapy system, aptly called ViewRay (developed by an Oakwood Village, Ohio, company).

To receive treatment on this machine, women undergo a planning MRI in addition to the CT scan, which sometimes reveals additional soft tissue detail that can be helpful in identifying the lumpectomy site.

The major advance of this treatment method, however, is the system’s ability to visualize the lumpectomy cavity before and during the delivery of each treatment. Rather than relying on surrogate landmarks for daily positioning, we can now be completely confident that the lumpectomy site is within the radiation dose delivery region. The ViewRay system also allows us to analyze movement of the surgical cavity during treatment delivery, such that treatment will be temporarily interrupted if the cavity moves beyond a prespecified distance (~3 mm, Figure B).

This knowledge makes it possible to target the surgical bed and surrounding tissue, without adding additional volume only to account for setup variability.

Furthermore, we have the opportunity to quickly identify changes that may have occurred in the breast anatomy (ie, interval reabsorption of seroma/ hematoma) and replan our radiation dose.

The aims of our clinical study include studying motion of the lumpectomy cavity and adjacent organs (ie, lungs, heart), as well as measuring actual radiation dose delivered to these tissues and compare actual versus planned dose. Andrzej Wojcieszynski, MD, currently a radiation oncology resident at the University of Wisconsin, presented preliminary results of our study at this year’s American Society for Therapeutic Radiation Oncology (ASTRO) annual meeting in Boston.

Future studies could compare outcomes of conventional versus MRI-guided boosts to determine IBTR and fibrosis rates achieved with optimized cavity delineation and treatment delivery.

References

1. Early Breast Cancer Trialists’ Collaborative Group, Darby S, McGale P, et al. Effect of radiotherapy after breast-conserving surgery on 10-year recurrence and 15-year breast cancer death: meta-analysis of individual patient data for 10,801 women in 17 randomised trials. Lancet. 2011;378(9804):1707-1716.
2. Bartelink H, Maingon P, Poortmans P, et al. Whole-breast irradiation with or without a boost for patients treated with breast-conserving surgery for early breast cancer: 20-year follow-up of a randomised phase 3 trial. Lancet Oncol. 2015;16(1):47-56.
3. Vrieling C, Collette L, Fourquet A, et al. The influence of patient, tumor and treatment factors on the cosmetic results after breast-conserving therapy in the EORTC ‘boost vs. no boost’ trial. EORTC Radiotherapy and Breast Cancer Cooperative Groups. Radiother Oncol. 2000;55(3):219-232.

Radiation therapy has been clearly shown to reduce the risk for in-breast tumor recurrence (IBTR) after breast conserving surgery.¹