What is staged radiosurgery?
Staged radiosurgery, also known as fractionated stereotactic radiosurgery (FSR), is a process in which the total dose of stereotactic radiation is divided into several smaller doses of radiation, with each dose delivered on separate days of treatment.
If staged radiosurgery is utilized, it typically consists of 2 to 5 treatments. As a point of comparison, staged radiosurgery is best contrasted with standard single fraction radiosurgery.
What are the indications of staged radiosurgery?
The main rationale for staged radiosurgery is to deliver an effective treatment to a tumor while minimizing any injury to nearby normal structures. In some situations, such as the radiosurgical ablation of acoustic neuromas, staged treatment effectively kills the tumor while apparently lowering the incidence of side effects (hearing loss and facial weakness/numbness) compared to single dose radiosurgery.
In other clinical circumstances, such as tumors in or around the optic nerve, staged radiosurgery permits treatment of tumors that could not otherwise be safely treated with conventional single dose radiosurgery. For many larger lesions, i.e. greater than 3 centimeters in diameter, staged radiosurgery can often be of value as well.
What are the advantages of staged treatment?
The primary advantage of staged radiosurgery is that it appears to reduce the risk of treatment complications or side effects. By delivering several smaller doses of radiation spaced more than 12 hours apart, the small amounts of normal tissue surrounding the tumor are allowed to “recover” before the next dose of radiation is administered.
This period of “recovery” is thought to reduce injury to the normal tissue around the tumor. Staged radiosurgery often represents a treatment option for patients who are not considered candidates for single dose radiosurgery due to tumor size, location, or other factors.
How does the physician determine number of stages?
The number of stages that a physician might recommend is based on a variety of circumstances but especially tumor size and location. Generally it is not the tumor itself, (i.e pathologic diagnosis) but rather its proximity to critical structures such as the hearing (cochlear) or vision (optic) nerve that determines the number of stages.
For example, if a tumor is next to the optic nerve, the maximal treatment dose tolerated by this nerve is likely to be the main determining factor for the number of treatment sessions. Among the diverse group of patients who are candidates for treatment with the CyberKnife, nearly all can be managed safely and effectively in five or fewer stages.
What is the procedure for staged radiosurgical treatment?
The process for staged radiosurgery on the CyberKnife is very similar to a single session treatment. The patient is placed on the treatment table and treated with radiosurgery. However, in the case of staged radiosurgery, only a portion of the total dose is administered during a given treatment. The remaining dose is delivered in near identical fashion on subsequent days.
How far apart is each stage delivered?
There is not any definitive data indicating the optimal time period between successive stages. The longer the period of time before the next treatment, the greater the probability that the normal tissue around the tumor will recover from any radiation injury. However, if too much time passes, then the tumor will also recover from some of the effects from the first dose of radiation.
The most commonly used technique for staging CyberKnife® radiosurgery is to administer consecutive doses of radiation over successive days. This current practice seems to strike a balance between normal tissue recovery and optimizing the likelihood of killing the tumor.
|
