From the July 2011 issue of HealthCare Business News magazine
Even systems designed to treat extracranial targets, including many gantry-based devices, need to account for motion in order to achieve desired levels of accuracy. Some systems employ motion compensation techniques to minimize exposure of healthy tissue. For example, when treating lung tumors, techniques might include respiratory gating, breath holding and abdominal frames. All of these require patients—many with already compromised lung function—to perform difficult breathing maneuvers or be placed in uncomfortable positions. In addition, they are all based on assumptions about tumor location and the patient’s breathing pattern—it’s an imperfect science and ripe with the potential for inaccuracy.
Likewise, when treating prostate cancer, some gantry-based radiosurgery systems rely on pre-treatment CT scans to initially set up the patient and guide treatment planning. The problem is that pre-treatment scans represent a snapshot in time; because patients are not static throughout the treatment and the systems are unable to deliver radiation fast enough to overcome movement, this approach is not always accurate and healthy tissue still is subject to injury.
Building on many of the motion management challenges inherent in gantry-based systems, some advanced radiosurgery systems have now made not only tumor tracking, but also automatic radiation beam correction during treatment, a reality.
For example, there are now systems that leverage sophisticated and continual image guidance software to track lung tumors during respiration. These devices recognize even the slightest shifts that might occur and automatically correct for intra-fraction tumor motion in real time and throughout treatment. In short, these systems are able to “synchronize” radiation beam delivery to lung tumor motion, allowing clinicians to significantly reduce treatment margins and achieve maximal sparing of critical structures without the need for gating, breath holding or frames.
While movement in the lung tends to follow the rhythmic pattern of respiration, the prostate presents a unique challenge in terms of motion management. As a result of gas or fluid in the bowels, the prostate is subject to random and excessive target motion that can make it difficult to achieve high levels of accuracy. Conventional radiation therapy systems, in particular, are unable to respond automatically to unexpected prostate motion during treatment.
