For decades, whole breast radiation therapy has been standard treatment for breast cancer patients following lumpectomy. The goal of radiation treatment is to kill any remaining cancerous cells around the lumpectomy cavity while limiting the dose to normal, healthy tissues, such as the heart and lungs. Recently, partial breast irradiation (PBI) has gained momentum in efforts to reduce the overall treatment time and limit the volume of breast and normal tissues being irradiated. This involves targeting only the lumpectomy cavity surrounded by a small margin to account for variability in daily treatments.
CT imaging has been the standard tool used for radiation treatment planning and has provided clinicians with great anatomic detail. However, CT is limited in its ability to visualize certain soft tissues, such as lumpectomy cavities, and its ability to distinguish them from adjacent normal tissue. Uncertainty in identifying the borders of the lumpectomy cavity can cause either undertreatment of areas at risk or unnecessary overexposure of healthy tissue to radiation in some patients.
In addition, another challenge is the fact that a lumpectomy cavity can move and change shape as the tissue heals in the weeks following surgery. Traditionally, physicians have relied on the surgery scar to serve as a marker to localize the lumpectomy cavity. Several studies have found that locating the lumpectomy cavity based solely on this scar may result in a partial miss of the cavity in over 50% of cases. While the radiation oncology community widely recognizes inconsistent set up of patients on the radiation table and changes to the lumpectomy cavity over time, one practical solution to this problem is to visualize the cavity on a daily basis using image-guided radiation therapy.
Benefits of 3D Ultrasound
Until recently, there were few options for visualizing the actual lumpectomy cavity to ensure the precise delivery of radiation. A new application of 3D ultrasound is being used to address this challenge and is gaining ground in the treatment of breast cancer. Ultrasound imaging is a safe and proven technology. Unlike traditional x-rays or CT scans, ultrasound imaging does not add an unnecessary radiation dose to the patient. In addition, ultrasound is well-suited to define the edges of a fluid filled cavity, often with greater accuracy than CT.
With this new application of ultrasound technology, radiation oncologists can increase their certainty and confidence in targeting radiation without added radiation doses. The ultrasound images are useful in defining the lumpectomy cavity at the initial treatment planning step. They may also help to verify accurate targeting on a daily basis prior to each treatment. If applied properly, 3D ultrasound could allow radiation oncologists to tighten the margins they’re treating, resulting in reduced radiation exposure for patients.
Precision in targeting radiation has never been more critical than it is today with the emergence of partial breast irradiation. With the percentage of PBIs conservation therapy and PBI continuing to rise, having greater certainty and confidence that radiation is being delivered to the exact area where its needed most is paramount. The novel use of 3D ultrasound marks an important first step in addressing this need.
Readings & Resources (click to view)
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For a press release on the release of the expert consensus document from the Society for Cardiovascular Angiography and Interventions, go to http://www.scai.org/drlt1.aspx?PAGE_ID=5871. The full document can be found at http://www.scai.org/pdf/20090507StatementPCICCI.pdf.
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