Brachytherapy

Brachytherapy refers to a method of delivering radiation to a tumor by placing radioactive sources either directly into the tumor or very close to it. By having the radioactive source close to the tumor, the radiation does not have to travel through normal tissue before it reaches the tumor. Furthermore, because the dose rate drops off rapidly as the distance increases from the source, very high doses of radiation can be delivered to the tumor while keeping the dose to surrounding normal tissue at a minimum.

Although the physical advantages of brachytherapy were known soon after the discovery of radioactivity, there still were many challenges that limited clinical application of brachytherapy. For example, it is difficult to treat a deep-seated tumor using brachytherapy. The physical size of the isotope, placement of the isotope, and radiation exposure to hospital personnel limited the application and quality of brachytherapy. Brachytherapy also produces a highly heterogeneous dose distribution because dose around the radioactive sources is much higher than a region just a few millimeters away. This complex dosimetry and lack of proper instruments to analyze it limited its application and slowed the progress of brachytherapy. Despite these limitations, excellent results using brachytherapy in various types of tumors have been well documented.

Recent discoveries in science and technology have lead to significant breakthroughs in the application and delivery of brachytherapy. New imaging modalities and faster computer have significantly improved the quality of the treatment and widened the application of brachytherapy in oncology. Elegant ultrasound and/or CT/MR-guided implant procedures allow radiation oncologists to apply brachytherapy in the most difficult clinical scenarios These techniques enable the radiation oncologist to visualize the tumor while placing the radioactive isotope or after-loading catheter. The utilization of these minimal invasive image guide procedures has dramatically improved the quality of implants.

The development of remote after-loading techniques and computer optimized treatment delivery systems opens new opportunities for brachytherapy to improve the therapeutic ratio and bring better tumor control while minimizing potential side effects. Modern remote after-loading brachytherapy treatment units use robotic technology to move a single (1-mm diameter) radioactive source precisely through surgically implanted plastic catheters (15 gauge). Using three-dimensional computer treatment planning software, the amount of radiation delivered along the catheter can be precisely controlled. In most cases the computer optimized treatment planning decreases the dose heterogeneity within the treated volume, however in special cases where higher dose to a region within the treatment is deemed beneficial, the "hot spot" can be applied to that region. Modern brachytherapy takes full advantage of physical dose distribution produced by the radioactive isotope.

Because of the unique physical dose distribution produced by brachytherapy, it can be applied to a variety of unusual clinical situations besides being a part of the definitive treatment. For example, brachytherapy can be use as a salvage treatment in a region that has been previously irradiated. The utilization of brachytherapy is highly dependent on the experience of the physician and the available resources. Therefore, it is important to consult a radiation oncologist with special expertise in brachytherapy for discussion.