Feature | September 03, 2014 | Raissa Rocha

IMRT, IGRT Continues to Grow in Use Among Arc-based Radiotherapies

This article appeared as an introduction to a Comparison Chart on Arc-based Radiotherapy Systems in the September 2014 issue.

Arc-based radiation therapy continues to gain ground as physicians opt for treatment options that not only are more precisely tailored to each tumor site, but also delivered in fewer visits, which is significantly more convenient for both patients and cancer centers. With a variety of radiation therapy techniques available, from intensity-modulated radiation therapy (IMRT) and whole-body irradiation (WBI) to proton therapy and stereotactic body radiation therapy (SBRT), cancer centers around the country are now, more than ever, able to offer patients a more effective solution for targeting and treating their diseases.

Types of Techniques

Recent advances are allowing radiation oncologists to use arc-based therapies to target a wide range of cancers, including prostate, breast, and head and neck. Not all solutions will work for all cancers, nor will all patients be suitable for all solutions, but each will typically deliver high radiation doses to the tumor site while minimizing damage to surrounding healthy tissue.

The reasons for radiation therapy can vary. Adjuvant radiotherapies target surgical sites to sterilize residual cancer; for example, an oncologist may use radiation therapy on lumpectomy cavities to treat any remaining cancer cells in the breast. Arc-based radiotherapy can also be used prior to operations, sterilizing areas around the tumor site to improve surgical outcomes. Radiotherapy may also be used to alleviate symptoms associated with tumors or to eliminate cancer cells entirely if possible.

The increasing use of multileaf collimators (MLC) has led to oncologists delivering higher energy X-rays deeper under the skin to more accurately penetrate tumors. In an MLC, each leaf is adjusted independently to block any part of the radiation field, allowing for beams to conform to the shape of the tumor and avoid healthy tissue. The latest MLCs typically have up to 160 leaves; Elekta’s Agility system is one example of intelligent beam-shaping technology. Siemens Healthcare also offers a 160-leaf MLC in several of its linear accelerators.

IMRT is one radiotherapy treatment that has been growing quickly in adoption and is considered to be standard in some cases. The technique actively modulates radiation beams around the patient during delivery, changing not only in direction but in intensity as well. One form of IMRT, Accuray’s TomoTherapy system, uses computed tomography (CT) imaging to ensure patients are correctly aligned on the day of their customized treatments. TomoTherapy was recently cited by MD Buyline in its Q2 2014 Market Intelligence Briefing as having the highest composite overall user satisfaction rating among radiation treatment delivery systems, along with the CyberKnife robotic radiosurgery system, also by Accuray.

Another form of radiotherapy, volumetric-modulated arc therapy (VMAT), expands on the concept by offering arc-based radiation that is continuous and uninterrupted, rather than in a stop-and-go procedure in which patients receive external radiation from a set number of orientations, or slices. Elekta’s Versa HD system offers VMAT capabilities with high-definition, high-speed beam shaping over a 40- by 40-cm field; it received 510(k) clearance from the U.S. Food and Drug Administration (FDA) in 2013. Institutions that have installed the Versa HD since then include HM Hospitales in Spain, Johns Hopkins Hospital in Baltimore and Swedish Medical Center in Seattle.

Similarly, Varian Medical Systems’ RapidArc technology delivers sculpted 3-D dose distribution with a single 360-degree rotation of the gantry. Treatment time is faster than IMRT, but requires a similar procedure, allowing for easier implementation. Varian offers RapidArc on all new Trilogy delivery systems and Clinac iX linear accelerators.

Radiotherapy Advancements

There are many add-ons and enhancements available for cancer centers looking to improve their arc-based radiotherapy arsenal. The use of real-time image guidance (also known as image-guided radiation therapy, or IGRT) allows physicians to more precisely localize and target tumors within the body without compromising healthy tissues. IGRT may involve the use of CT datasets or matching radiographs in order to determine coordinates.

Another imaging modality, magnetic resonance imaging (MRI), is under consideration for future use in radiotherapy image guidance. ViewRay Inc. showcased its MRIdian system, an MRI-guided radiation therapy system, at the 2014 annual meeting of the American Association of Physicists in Medicine (AAPM) in July. Dubbed the world’s first and only such system, the MRIdian is designed to improve cancer treatments with continuous soft tissue imaging, allowing clinicians to localize the cancer and monitor where radiation doses are being delivered.

Elekta and Philips Healthcare’s research consortium to develop an MRI-guided radiotherapy system reached seven members in August, with the addition of The Christie NHS Foundation Trust, a Manchester, England-based cancer center. Other members of the consortium include the University Medical Center Utrecht, the Netherlands; the University of Texas MD Anderson Cancer Center, Houston; and the Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital, Amsterdam, among others.

The number of arc-based radiotherapy options in the market continues to grow with each new advancement that promises to deliver more precise radiation doses to more localized tumor sites, improving cures and quality of life for patients. With many vendors offering solutions, cancer centers looking to improve their programs with high-quality technologies should seek systems that best fit their needs.

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