IGRT, Cone-beam CT Fine Tune Cancer Treatment

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Image-guided radiation therapy (IGRT) coupled with on-board cone-beam CT are delivering dramatic improvements in the radiation therapy process. By carefully pairing images and treatment, IGRT and cone-beam CT allow radiation oncologists to increase the dose, spare more normal tissue, and ultimately, improve patient outcomes.

Take for example Henry Ford Health System in Detroit, Mich. The system is heavily invested in radiation therapy and treats more than 200 patients daily at five sites. “Henry Ford Health System is very active in the latest technology and treatment including stereotactic radiosurgery and intensity-modulated radiation therapy (IMRT) with millimeter accuracy. IGRT is essential to our success,” shares Ben Movsas, MD, chair, department of radiation oncology.

Others share Movsas’ enthusiasm for IGRT. “IGRT is becoming the standard of care,” says Carol Nass, chief radiation therapist at The William Backus Hospital in Norwich, Conn. One of the latest developments in IGRT is on-board cone-beam CT, and sites are turning to the technology to provide improved patient care.

Boosting accuracy

Henry Ford Health System is equipped with two Varian Medical Systems Trilogy Tx, an image-guided radiosurgery system with plans to deploy a third system and a BrainLAB Novalis Tx Adaptive Gating system (developed in partnership with Varian) later this year. Each system incorporates on-board cone-beam CT.

Although IGRT can use CT, ultrasound or radiography and fiducial markers for image guidance, Movsas says cone-beam CT carries a number of advantages. “Cone-beam CT allows non-invasive image guidance of any site in the body. Placing a fiducial marker in the lung, on the other hand, could complicate the patient’s condition by causing a pneumothorax. Not all organs can be imaged well with ultrasound.” Unlike KV x-ray, CT provides tumor volume data and detailed anatomical information.

IGRT improves on conventional radiation therapy planning, which acquires a simulation CT days prior to treatment. “We know structures move. On-board cone-beam CT provides the extra accuracy to verify that the radiation beam is on target,” says Movsas.

 Movsas explains that a key advantage of the on-board cone-beam CT scan is that it enables comparison with the initial planning CT to verify the target volume prior to treatment delivery. There is no room for error, says Movsas, as the stereotactic lung protocol is based on four ultra-high radiation doses in a two-week period rather than six or seven weeks of daily treatment. Each session delivers 1200 cGy (or “rads”) compared to 200 cGy per day in a conventional regimen. “It’s very intense from a biological standpoint,” says Movsas. The radiation therapy team makes adjustments in about 15 to 20 percent of cases based on IGRT results. The Henry Ford uses cone-beam CT to verify treatment targeting for a variety of sites, ranging from prostate to pancreatic cancers.

Early data indicate that the regimen works. “Standard 3D conformal treatment yields local control of tumors even in early stage lung cancer about 50 percent of the time,” reports Movsas. “The stereotactic model is more efficient, better tolerated and more effective, delivering local control in about 90 percent of cases.”

Although Henry Ford Health System also uses stereotactic treatment for spine tumors and other sites, the department strives to prevent over-utilization of the technology. A dedicated tumor board, consisting of surgeons, radiologists, stereotactic nurses, radiation therapists and medical oncologists, meets regularly to discuss appropriate case management for stereotactic treatment, referring some to chemotherapy, IMRT, surgery or other biological therapy as necessary.

The radiation therapy department at The William Backus Hospital took a different path to the IGRT program. The hospital installed Elekta Synergy with 3D x-ray volume imaging in July 2006 and uses integrated cone-beam CT to treat most prostate cancer patients.

The IGRT protocol is built on daily CT imaging. Images are acquired and digitally overlaid on a reference image to localize the prostate prior to daily treatment. Patients are shifted accordingly if images show prostate movement. Although the protocol produces highly accurate visualization of the target and uses more imaging data, it does not add a workflow burden. “Other than head and neck IMRT cases, which can take 30 minutes, treatment is delivered in a standard 15-minute time slot,” says Nass. The hospital has built on its successful start and is integrating the cone-beam CT system into head and neck, esophagus, brain and gastric cancer treatment.

Getting started

IGRT is a new clinical model that can bring significant patient benefits. “It’s a new way of thinking for radiation therapists. The model requires therapists to use the software in conjunction with their skills and experience for daily image registration to localize tumor volume. It isn’t difficult, but it is different,” says Nass. She recommends sites interested in IGRT protocols learn more about the technology via a site visit or American Society for Therapeutic Radiology and Oncology (ASTRO) meeting.

The William Backus Hospital radiation therapy department took a staggered approach to training; four therapists, three physicians, a physicist and dosimetrist completed four days of on-site training in treatment delivery and electronic portal imaging when the linear accelerator was installed. One month later, the team completed cone-beam CT training and started imaging patients. “It gave us time to get used to the system,” says Nass. The department also shared information about the technologies with the referring physician community, so they understand the appropriate applications for and benefits of the approach.

Another essential element of successful programs, says Movsas, is a dedicated IGRT team. Henry Ford Health System created a multidisciplinary, experienced team with representation from nursing, surgery, medical oncology and radiation therapy, to steer the development of the program.

Future directions

Henry Ford Health System plans to deploy Novalis adaptive respiratory gating system later this year. The new deployment should increase treatment accuracy by tracking and correlating internal motion of lung tumors during treatment delivery.

On target

IGRT is the platform for more accurate delivery of radiation therapy in a number of cancers, particularly those characterized by tumor motion. On-board cone-beam CT provides a workflow neutral option that allows radiation therapy teams to implement highly individualized treatment and potentially deliver improved patient outcomes.