Doc-to-Doc: Image-Guided Gynecologic Brachytherapy
Elizabeth Kidd, MD is Acting Assistant Professor, Radiation Oncology – Radiation Therapy at Stanford University Medical Center. Her clinical practice focuses on radiation oncology, gynecologic malignancies, breast cancer, thyroid cancer and brachytherapy. To contact Dr. Kidd about speaking engagements, please send an email to outreach@stanfordmed.org. Patient referrals can be faxed to 650-320-9443 or call the Physician Helpline at 866-742-4811referral@stanfordmed.org.
The field of radiation oncology has changed dramatically over the last 10-15 years, with a greater focus on minimizing dose to normal tissues and decreasing toxicity. Technological advances in imaging, treatment planning, and treatment delivery have come together to allow for improvements in radiation treatment.
More and more institutions are utilizing three-dimensional (3-D) imaging, with CT or MRI, for gynecologic brachytherapy treatment planning. Brachytherapy is a means of delivering radiation in which a radiation source is placed in very close proximity to the area requiring treatment and it is often a component of treatment for cervical, endometrial, and vaginal cancers.
Brachytherapy may be given on its own, such as after surgery for an early stage endometrial cancer with high-intermediate risk factors. Alternatively, brachytherapy may be used along with external beam radiation and chemotherapy, such as for the definitive treatment of cervical cancer.
One benefit of brachytherapy is that radiation is only delivered to a localized area around the radiation source. This requires careful placement of the brachytherapy applicator and awareness of the normal tissues that lie in close proximity to the treatment site. Generally, applicators are placed, the patient is imaged with the applicator in place, a treatment plan is developed, and then the radiation is administered through the applicator.
Historically, imaging was done with 2-D orthogonal x-rays, this method provided more limited information about the placement of the applicator, and the dose of radiation to adjacent organs. Performing 3-D imaging with the brachytherapy applicator in place, prior to delivering radiation, allows for verification of the placement of the treatment device, visualization of the target treatment site and surrounding normal tissues.
The bladder, rectum, and bowel are the primary organs at risk with gynecologic brachytherapy. Their position and degree of filling can change dramatically between implants, so imaging with each implant placement is recommended.
Some of the initial work involving 3-D image-guidance for gynecologic brachytherapy investigated the actual radiation doses received by the surrounding normal tissues. Studies suggest that determining the minimum dose to the most irradiated tissue, for example the highest dose received by 2 cc of the rectum, has the best correlation with the risk of toxicity. There has also been some preliminary work for defining standards for contouring targets using 3-D imaging information.
Using 3-D imaging for gynecologic brachytherapy allows for the contouring of the target treatment region and the surrounding organs at risk. With 3-D planning, the coverage of the target and dose to normal tissues can easily be determined, which can allow for modifications to obtain better coverage of the target or decreased dose to organs at risk. Image-guided gynecologic brachytherapy has the potential to improve disease outcomes and decrease treatment-related toxicity.
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