February 10, 2009
Cervix Moves Significantly More Than Previously Thought During Radiation for Cancer
Radiation and gynecologic oncologists at the Moores Cancer Center at the University of California, San Diego are concerned that many women with cervical cancer may not be receiving the optimal dose of radiation during treatments specific for the shape of the tumor because the cervix may be moving too much. They recommend that radiation oncologists need to take such movement into account to make sure the cervix remains in the treatment field.
The team presented its findings – the first to look at cervix movement during radiation therapy – on February 6, 2009 at the Society of Gynecologic Oncologists’ 40th Annual Meeting on Women’s Cancer in San Antonio.
The researchers found that the cervix moved significantly more than previously thought during radiation therapy, possibly affecting treatment. As a result, radiation oncologists may have to spare less healthy tissue than they would like to effectively treat the cancer.
According to Catheryn Yashar, MD, assistant professor of radiation oncology at the UC San Diego School of Medicine and chief of breast and gynecological radiation services at the Moores UCSD Cancer Center, who led the work, one of the difficulties in using radiation in treating cervical cancer is that the cervix frequently moves during and between treatments. This may be caused by the bladder filling, pockets of gas in the rectum and tumor shrinkage as the therapy progresses, making treatment planning difficult when using precise radiation therapy such as IMRT (intensity modulated radiation therapy).
To determine how much the cervix was moving during radiation therapy, Yashar and her co-workers monitored 10 patients diagnosed with cervical cancer between 2007 and 2008. All patients had two cervical “seeds” placed, which enabled images to be taken of the cervix. Yashar’s team looked at more than 500 scans, or 50 per patient. While the researchers found that cervical movement during and between treatments may average from 2 to 5 millimeters, they were surprised to find that the cervix moved in some cases as much as 10 times more, or 2 centimeters, between daily treatments and even during daily treatments.
“The study implies that you have to be very careful from the beginning to the end of treatment,” Yashar said. “To account for movement and to be sure the cervix is in the treatment field, you have to either give large treatment margins, which decreases the sparing of normal tissues, like bladder and rectum, or you have to use image guidance. Image guidance monitors the position of the cervix and signals when changes in the radiation treatment plan are necessary.”
IMRT can be effective in treating cervical cancer, and compared to irradiating the entire pelvis, it can potentially spare surrounding structures, such as the bowel and bladder, from radiation, Yashar said.
“What is unique with this study is that we use two gold seeds as surrogate markers for the cervix and performed daily imaging both before and after treatment. That shows us not only the movement of the cervix between Monday and Tuesday but also between the beginning and end of treatment. It’s not the average daily motion, but rather the maximum motion that is the most important.
“We need research to be able to predict which patient’s cervix might move 2 cm during treatment. We have to go back and look at those patients who have the maximum movement during treatment and see if we can figure out why that is and predict it. If we can predict it, maybe we can prevent it or at least know it is going to happen. Future research will have to solve this problem – how to keep the cervix in our sights and still spare healthy tissue.”
Cervical cancer is the fifth most common cancer in women worldwide with approximately 471,000 new cases diagnosed each year, though only about 11,000 cases of invasive cervical cancer were expected last year in the United States, with about 3,800 deaths. The majority of cases are caused by infection with the human papillomavirus (HPV). Cervical cancer can be a significant problem, particularly in underserved populations, Yashar noted.
Other UCSD coauthors on the report include Cheryl Saenz, MD, A.J. Mundt, MD, and Nora Haripotepornkul, MD.
The Moores UCSD Cancer Center is one of the nation’s 41 National Cancer Institute-designated Comprehensive Cancer Centers, combining research, clinical care and community outreach to advance the prevention, treatment and cure of cancer.
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