Positioning Pelvic Cancer Patients On Stomachs For Radiation Yields Better Results

"It was a surprising finding," according to according to Martin Fuss, M.D., the director of the Program in Image-Guided Radiation Therapy, OHSU Radiation Medicine, and OHSU Cancer Institute member.

"This finding runs contrary to the common perception that the supine (on the back) position is more stable, convenient and therefore caused less variation in day-to-day setups. Variation in setups require the use of margins that extend beyond the tumor into normal tissues, exposing organs with limited tolerance to radiation to a higher risk for treatment-induced toxicity," said Fuss, who is also a professor in the OHSU School of Medicine.

Having a patient lay on his belly, or prone position, has been considered to be uncomfortable and can lead to more patient movement, which can cause more damage to healthy cells that need to be spared from high-dose radiation. But through this study it was found that lying on the stomach, using a belly board, with a hole cut out for the stomach area, may actually aid in sparing normal tissue. Lying on a belly board not only removes the bowel from the pelvis but also reduces pelvic setup variation. The type of radiation used in this study was helical TomoTherapy.

The TomoTherapy system used allows physicians to take a computed tomography or CT scan just before each treatment. With the scan, radiation specialists can verify the position of the tumor and, if necessary, adjust the patient's position to help make sure the radiation is directed right where it should be. This process is also referred to image-guided radiation therapy or IGRT. The treatment system in the study, TomoTherapy Hi•Art, delivers intensity-modulated radiation therapy (IMRT) with a helical, or spiral delivery pattern.

In the study 30 patients were treated with IMRT under daily image guidance. Of those, 11 were prone and 19 were supine. Prone setup always included a belly board. A total of 829 megavoltage CT image-guided studies were acquired. All patients received image-guidance before radiation to determine how much correction of the radiation beam was needed.

A poster presentation from this study "MVCT Image-Guidance Derived Bony Setup Accuracy for Supine and Prone Pelvic Radiation Therapy was presented  Oct. 28 at the 2007 American Society of Therapeutic Radiology and Oncology meeting in Los Angeles.

Other researchers include: Faisal Siddiqui, Ph.D., OHSU Radiation Medicine; Chengyu Shi, Ph.D., and Niko Papanikolaou, Ph.D., both from the Cancer Therapy & Research Center, medical physics and University of Texas Health Science Center, San Antonio, radiation oncology.