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