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April 7 , 2008

EBRT and IOERT: A Winning Combination
By Donald A. Goer, PhD
Radiology Today
Vol. 9 No.7 P. 29

The past decade has seen an explosion in new technology for external beam radiation therapy (EBRT) cancer treatment, including 3D conformal radiation therapy, intensity modulated radiation therapy, tomotherapy, image guided radiation therapy, respiratory gating, and proton therapy. These EBRT technologies are designed to provide precise dose delivery and allow for safer dose escalation. They have been widely adopted even though they are still new and evolving. In some cases, they have reduced normal tissue toxicity but have yet to demonstrate improvement in either local control or cure.

Many EBRT innovations are time consuming to plan and implement, often resulting in a reduction in the volume of patients that can be treated. For some busy centers, this will result in increased waiting times to begin radiotherapy, which are recognized as having negative consequences on patient outcomes.

Expanding EBRT facilities to accommodate these new technologies has also been costly in equipment, space, increased personnel necessary to operate the new equipment, and construction of the shielded EBRT rooms. Hospitals, administrators, and healthcare systems are faced with the dilemma of how to best allocate their capital resources to invest in these promising new technologies before they have matured without compromising their ability to treat a growing number of cancer patients. Until recently, there was no clear solution to these cost and complexity hurdles. However, a new implementation of a mature clinical technology could be the answer to this dilemma.

Mature Technology With New Results
Intraoperative electron radiation therapy (IOERT) is the application of electron beam radiation directly to a tumor or tumor bed during surgery. During IOERT, most of the tumor is removed through conventional surgical techniques. Radiation is then directly applied to the area immediately surrounding the tumor while still exposed during surgery. IOERT is generally most effective as a precision boost—a high dose of radiation therapy at the time of surgery—followed by traditional EBRT postoperatively.

By using IOERT, healthy tissue that normally surrounds the target structure when delivering an external beam boost or dose escalation is displaced and/or protected, which significantly enhances the therapeutic ratio. Furthermore, IOERT boosts may have some biological advantages over external beam boosts or dose escalations given many weeks postsurgery.

Since IOERT is delivered at the time of surgery, when residual tumor cells are most vulnerable, a tumorcidal dose is delivered to the tumor bed before the tumor cells have the opportunity to reimplant, proliferate, or migrate. This lowers the tumor burden for any adjuvant EBRT, radiation, or chemotherapy treatment. IOERT replaces two to three weeks of conventional, fractionated radiotherapy treatments, reducing the number of EBRT fractions that must be delivered. A precision IOERT boost, combined with precisely delivered but reduced numbers of EBRT fractions, achieves the goal of precision radiotherapy dose delivery with the added benefit of reducing the EBRT patient volume (ie, fewer EBRT fractions for treatments that also have IOERT as a component of treatment). Additionally, IOERT has demonstrated an improved local control for many advanced cancers when compared with patients treated with advanced disease but without IOERT.

A New Breed of Linear Accelerators
The widespread adoption of IOERT has been limited by the difficulty of using conventional electron accelerator technology to deliver it. To receive IOERT, patients were either transported from the operating room to the radiation department in the middle of a surgical procedure or costly shielded bunkers were constructed in the operating theater to house a conventional linear accelerator. The complex logistics of patient transportation and the cost of constructing a shielded bunker in the operating theater have limited the availability of IOERT until now.

Newer models of mobile electron linear accelerators, such as the Mobetron manufactured by IntraOp Medical Corp., are self-shielded and small enough to reside in almost any unmodified hospital operating room, allowing IOERT to be delivered more simply and inexpensively. These devices make IOERT a realistic and cost-effective approach for hospitals to consider integrating into their cancer programs.

Combining a precision boost of IOERT with the new EBRT technology enhances local control while reducing the number of EBRT treatments required to adequately treat the disease. Patients benefit from higher local tumor control, shorter treatment cycles, fewer side effects, and, in many cases, increased survival rates, as well as peace of mind and increased quality of life.

— Donald A. Goer, PhD, is the chief scientist and cofounder of IntraOp Medical Corp.