IORT - Intraoperative Radiation Therapy
Why Radiation?
The focus of Breast Conserving Therapy in the past 30 years has been devoted to lowering the cancer mortality rate while finding methods to provide the minimum treatment with maximum results—a kindler, gentler approach. For early stage cancers, this has produced a trend away from full mastectomies towards minimal breast tissue removal (lumpectomy) combined with six to seven weeks of radiation therapy.
The purpose of breast irradiation after lumpectomy is to prevent local cancer recurrence from any residual cancer cells. Traditionally, the entire breast has been considered at risk for local recurrence, so a series of lose-dose, external radiation treatments have always been given to the entire breast followed by radiation boost to the operative area. However, results of studies of the incidence and distribution of local recurrences with or without post-operative boost have led to reconsideration of how to administer radiation therapy.
Why IntraOperative Radiation?
Much of the risk of local recurrence after post-operative, external radiation boost has been attributed to inaccurate targeting of the boost. This data suggests that more intense and focused irradiation of the operative site, especially if given before residual cancer cells begin to multiply, should significantly reduce the risk of recurrence, possibly to the level where the series of whole breast radiation treatments are unnecessary. Therefore, radiation delivered during surgery which directly irradiates the tumor bed, referred to as intraoperative radiation therapy (IORT), has gained widespread popularity worldwide as an alternative to external, post-operative radiation therapy.
IORT is a technique in which a single higher dose of radiation is intraoperatively delivered to tissue immediately surrounding the removed tumor using either a photon-based (x-ray) or an electron-based emitter immediately after breast-conserving surgery and just prior to breast reconstruction. It is often referred to as “precision radiation” therapy since it is targeted just to the immediate tumor area through visual confirmation.
What Are The Types of IntraOperative Radiation?
X-ray (photon) IORT is a low energy source (up to 50 kilovolts) administered through spherical applicators of various diameters. After tumor excision, the applicator that best fits into the cavity is selected and the cavity is closed around it. Due to the steep depth-dose curve of the low-energy x-ray radiation, no shielding of the heart or lungs is required. Radiation delivery is typically accomplished in 25 to 30 minutes, after which the applicator is removed and the wound closed through oncoplastic reconstruction. Oncoplastic reconstruction is a method developed in Europe where the remaining breast tissue is reshaped to retain its natural contours.
Electron-beam IORT is a high energy source (up to 12 megavolts) applied through cylindrical applicators of various diameters and terminal angles. IORT can be delivered as a single dose or as a boost at about half the single dose. With single dose, an aluminum-lead shield is placed between the breast and the thoracic wall and the excision cavity is closed over it. Radiation delivery is usually accomplished in less than two minutes, after which the shield, if used, is removed and the wound closed through oncoplastic reconstruction.
Delivering IORT treatment in a single session is not a new concept. Older IORT techniques involved cumbersome machinery and/or required custom-built heavily shielded operating suites. Some institutions performed IORT by transferring patients from the operating room to the radiation oncology department during surgery.
The two distinctions of the IORT delivery method associated with SurRad ™ center around the exclusive use of the more advanced electron-based emitter technology in a mobile application. The more specific application of just electron-based radiation is referred to as IntraOperative Electron-Beam Radiation Therapy (IOERT). Two medical equipment suppliers presently manufacture a mobile, self-shielded, linear accelerator specifically optimized for IOERT—The Mobetron 1000 by IntraOp Medical Corporation of California and the Novac7 by Italy-based New Radiant Technology. Besides the higher energy output, another advantage of electron-based emitters is the ability to administer asymmetrical dose patterns to better replicate the irregular tumor bed.
What Is The Compelling Evidence In Favor Of IntraOperative Radiation Therapy?
For patients with early stage breast cancer, several randomized trials have demonstrated that IORT is a safe and effective replacement for external, post-operative radiation therapy according to “A Review Of The Literature” authored by Douglas E. Busby, MD, former Medicare Medical Director for Illinois. The trials also showed that the adverse effects of radiation and the risk of local cancer recurrence are much less with IORT. Many trials are noted in the Review including four conducted throughout Italy, the University of North Carolina’s Lineberger Comprehensive Cancer Center, and a joint study by the Medical College of Ohio and the Centre Regional de Lotte Contre le Cancer in Montpellier, France. The Montpellier trial showed zero recurrences at a median follow up of 25 months for 170 patients.
The most cited continuing trials have been performed by the Milan-based European Institute of Oncology directed by Dr. Umberto Veronesi (the Veronesi Study) . The EIO performed the IORT application using the Novac7 electron-beam accelerator on 185 patients from July 1, 1999 to October 31, 2001. The results as published in the European Journal of Cancer in 2001 reported that IORT “in the conservative treatment of breast cancer could allow the course of external fractionated-dose radiation therapy to be completely avoided; IORT dramatically reduces radiation exposure of the skin, lung, and subcutaneous tissues and avoids the irradiation of the contralateral breast…In our experience, IORT for limited-stage breast carcinoma is easy to perform and only briefly prolongs the duration of the surgical procedure.”
A subsequent trial conducted by the EIO from July 1999 to December 2007 again demonstrated that IORT is a safe method for conservatively operated breasts and reduces drastically the cost of radiation therapy. Only 0.5% of the patients in the trial developed local recurrences (compared to the U.S. recurrence rate of 11% to 15% for the many weeks of post-operative radiation therapy).
According to the Oxford Review, a global organization that has conducted randomized clinical trials in early breast cancer, for every four recurrences avoided, one less death from breast cancer will occur. With a U.S. breast cancer mortality rate still over 40,000 per year, a significant reduction in recurrence could save many more lives.