Medical Devices: IOERT for Colorectal Cancer

Colorectal cancer is the third leading cause of cancer in both men and women in the United States. Despite improvements in screening that result in detecting this disease in earlier stages, the disease remains the second leading cause of cancer death in men and the third in women. Each year, more than 50,000 people will succumb to the disease.

Conventional methods aren’t effective

Patients with locally advanced or recurrent colorectal cancer are difficult to treat effectively with conventional methods. Accepted levels of traditional external beam radiation treatment (EBRT) are insuffi cient to control advanced disease, and higher doses of EBRT would damage surrounding healthy tissue. EBRT boost is often technically diffi cult to achieve, due to the risk of small bowel involvement. An alternative is intraoperative electron radiation therapy (IOERT), the application of electron-beam radiation directly to a tumor or tumor bed during surgery. With 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.

New treatments with mature technology

For locally advanced rectal cancer, IOERT is particularly effective as a precision boost—a high dose of radiation therapy at the time of surgery—because, in the pelvis, surgery is confi ned to natural boundaries that often make it impossible to achieve a total resection. By using IOERT, radiation can be delivered to the area of highest risk, while healthy tissue—that might normally surround the target structure when delivering externalbeam boost or external-beam dose escalation—is displaced and/or protected during surgery, which signifi cantly enhances the therapeutic ratio. In the case of rectal cancer, the small bowel, bladder, and ureters can be excluded from the radiation field.

IOERT is delivered at the time of surgery, when residual tumor cells from the surgery are most vulnerable, so that a tumorcidal dose can be delivered to the tumor bed before tumor cells have the opportunity to re-implant, proliferate, or migrate. Because IOERT replaces two to three weeks of conventional fractionated radiotherapy treatments, the number of EBRT fractions that must be delivered prior to the surgery can be safely reduced, thereby minimizing gastrointestinal complications that sometimes occur from higher EBRT doses. A precision IOERT boost, combined with a smaller number of precisely delivered EBRT fractions, achieves the goal of precision radiotherapy dose delivery with the added benefi t of reducing complications from the EBRT component of the treatment.

Studies demonstrate that IOERT improves local control and survival rates in locally advanced cancer. A pooled analysis of 649 locally advanced rectal cancer patients showed a 5- and 10-year local control of almost 90% and a fi ve-year survival of 67%. Without IOERT, typical local control and survival at fi ve years is less than 60% and 40%, respectively. For recurrent rectal cancer, IOERT is one of the few treatments off ering any hope to patients who otherwise face a grim prognosis. Mobile linear accelerators:

Keeping cancer care accessible

The size of conventional linear accelerators and the shielding required make it prohibitively expensive to install them in most operating rooms. To combat this, mobile electron linear accelerators have been developed that allow IOERT to be delivered in almost any unmodifi ed hospital operating room. For example, the Mobetron, a mobile linear accelerator manufactured by IntraOp Medical, weighs only one-eighth as much as a conventional linear accelerator and requires no supplemental shielding. The Mobetron can be installed in virtually any operating room, and because it is mobile and motorized for transport, it can conveniently be used in more than one operating room, providing fl exibility in the scheduling of the IOERT treatment. Colon and rectal cancers are among the most common cancers in the United States. If not diagnosed at an early stage, these cancers can be diffi cult to treat with conventional methods. Treatment for colorectal cancer has improved over the last 10 years, resulting in more eff ective options for people with this type of cancer, including IOERT, which helps fi ght cancer at its source with a more precise radiation beam, shortens treatment cycles, and provides fewer side eff ects. Dr. Goer is the chief scientist at IntraOp Medical Corp.