Stereotactic Body Radiation Therapy is a technique designed to deliver a very high dose of radiation to a target lesion in the lung. There are a variety of platforms that are used to deliver this type of treatment including Imaged Guided Linear Accelerators and the Cyberknife.
Increasing evidence suggests that this technique might be very effective at eradicating the disease in the areas treated.
Recently, however, there have been reports of complications associated with this treatment approach. Unfortunately, complications associated with treatment are often underreported because it is more interesting to report positive data then negative data.
At the recent meeting at the American Society for Therapeutic Radiation and Oncology (ASTRO, the main US-based radiation oncology professional society), the incidence of severe pain and rib fracture were reported in a combined series from the University of Virginia and the University of Colorado. Dunlap and colleagues (abstract here) reported that 13 of the 31 patients with lesions that were with 1.5 cm of the chest wall underwent high dose stereotactic radiotherapy either experienced chest wall pain or rib fracture. Most patients who experienced rib fracture or chest wall pain experienced it around 7 months. When they evaluated the plans after the fact, they identified the risk of rib fracture or chest wall pain to be associated with high dose radiation in the region of the rib. This series suggested that if the volume of the chest wall that received over 30 Gy was greater than 40 cc the risk of complications approached 50%. Although this series is somewhat small, there is the suggestion that if one can use techniques to limit the high dose region that overlaps the rib/chest wall region the risk of rib fracture or chest wall pain will be less.
One of the important rules about radiation therapy is to be careful to avoid giving an excessively high dose to areas that aren’t forgiving. One of these areas that is very important is the brachial plexus, a bundle of nerves that comes off the spinal cord and runs near the clavicle just above/around the top part of the lung and then enters the shoulder and arm. These nerves supply the sensory and motor functions for the shoulder, arm, and hand.
Forquer and colleagues (abstract here) reported results of brachial plexopathy following SBRT. Damage to the brachial plexus occurred in 7 of 37 patients that had lesions that were located very high (in the very top part of the lung). This complication was described as shoulder/arm pain alone, pain and upper extremity weakness, and progression to numbness in the upper extremity with paralysis of hand and wrist. The injury was described 7 months after treatment in most patients. In evaluating the dose to the brachial plexus, it appears that the risk of injury occurred in 46% of patients when the maximum dose the brachial plexus exceeded 30 Gy (a “biological equivalent dose”, or BED (to be covered as the subject of a separate post), of 123 Gy), and occurred in only 8% of the patients when the brachial plexus dose was less than 26 Gy (a BED of 100 Gy).
These are just small studies, but they highlight that while SBRT is an exciting new approach in radiation oncology, it’s also a young field in which we’re gaining valuable new experience. That includes learning about new problems over time, as treated patients are followed and new research can be conducted on SBRT. These reports highlight that we can’t allow the clinical use of these new techniques run far ahead of the clinical research.