How SBRT Differs from Conventional Therapy
With conventional therapy, radiation is delivered in relatively small doses over the course of several weeks, with patients receiving daily treatments during that time. With SBRT, physicians are able to deliver a greater combined dose of radiation over the course of far fewer treatments. SBRT has shown dramatically better outcomes than conventional radiation therapy. Whereas two-year success rates for conventional treatment range from 30 to 40 percent, the success rates for SBRT range from 80 to 90 percent — comparable to those of resection surgery but with far fewer risks. Despite the fact that SBRT delivers higher biological dosage of radiation, patients have experienced fewer side effects, including radiation pneumonia. Slight fatigue for one week following treatment is SBRT’s most common side effect.
How SBRT Works
Planning begins with diagnostic imaging to help locate the tumor and determine the area that will be treated. This includes four-dimensional imaging that maps the target area as it moves over time with the patient’s breathing cycle. In the only invasive part of the treatment, gold seeds, called fiducials, are sometimes implanted into the tumor before images are taken. Because the fiducials are visible in planning scans and at the time of treatment, physicians use them to ensure that the high-dose envelope of radiation is accurately overlying the tumor.
Radiation oncologists work with medical physicists to develop a radiation plan that ensures safe exposure to normal structures. Each of the treatment sessions takes 30 to 60 minutes and, unlike with more invasive therapies, the patient leaves each treatment free of significant pain or side effects. Treatments do not have to be administered on consecutive days, but the entire course of therapy is usually concluded within 10 days.
Who Can Benefit From SBRT
Lung cancer candidates for SBRT are patients with small tumors — five centimeters or less — who are poor candidates for surgery due to the risk of functional deficit. Patients whose tumors are located centrally or close to airways or the heart have sometimes been considered poor candidates for SBRT due to higher complication rates. UCLA radiation oncologists have successfully treated these patients using slightly lower doses of radiation in combination with radiofrequency ablation. The two treatment modalities offer different toxicity profiles and provide good treatment of tumors with less risk to patients’ breathing function.
What are the indications for Stereotactic Body Radiation Therapy (SBRT)?
SBRT has been used for many localized tumors (up to 6-7 cm), or a few tumors (up to 3-5 usually) throughout the whole body. The list of tumors that has been treated successfully at UCLA and throughout the world with SBRT continues to grow. They include: primary lung cancer, and tumors that have spread to the lung, pancreatic tumors, bile duct tumors, primary and metastatic liver tumors, kidney tumors, prostate cancer, pelvic tumors, sarcomas, metastatic tumors throughout the body (otherwise known as oligometastases), and more. (see a list of other indications).
In certain highly selected circumstances, we may be able to offer SBRT as the modality of choice for patients that have previously received a full dose of external beam radiation therapy and now have recurrent but localized tumors. SBRT is a rapidly maturing technology that requires specialized clinical and technical expertise.
What is required to perform SBRT treatments for localized tumor?
SBRT requires highly accurate, precise, and focused radiation delivery in order to be successful because of the high dose of the treatment as well as the rapid radiation dose drop-off. It utilizes the same principles that have allowed Radiation Oncologists and Neurosurgeons to successfully deliver highly focused and precise radiation treatment to brain tumors, and brain metastases. Unlike the CNS, however, tumors and organs throughout the body can potentially move with breathing and other factors. SBRT treatments require accurate and precise tumor localization at the time of radiation simulation (Figure 4). Our expert team works closely with our interventional radiologists or surgeons to minimal invasively place into a patient's tumor, fiducials (tiny gold seeds, or coils) that act as localizing and tracking devices (Figure 5). Fiducials assist us in targeting the tumor more accurately and precisely. The placement of fiducials is a procedure much like obtaining a biopsy for the tissue diagnosis of the cancer and is safely performed under image-guidance.
SBRT requires accurate and custom mapping for each individual patient's anatomy and organ motion so that we may be able to optimally target the tumor and simultaneous spare the surrounding normal tissue. We utilize any and all potential imaging modalities such as PET, MRI, CT, as well as other novel imaging platforms to localize the tumor in four dimensions. It requires highly sophisticated radiation delivery systems not available in most radiation oncology practices. More importantly, it requires clinical expertise and experience which allow our expert Radiation Oncologists to make sound treatment judgments regarding a recommendation for SBRT. In addition, you can be assured that our expert team will competently follow-through with an efficacious and safe SBRT radiation plan at the time of treatment. Instead of several weeks of conventional radiation therapy, patients complete their SBRT in a short-period of time, usually over a 1 week period, minimizing the inconvenience of daily trips to the radiation oncology facility.