A new technique for tracking tumors in real time can maximize the radiation dose delivered to the tumor while sparing up to 50% more healthy surrounding tissue.

Ivan Buzurovic, PhD, and fellow medical physicists at Thomas Jefferson University and Jefferson’s Kimmel Cancer Center have developed a 4D robotic system that continuously tracks tumors during radiotherapy so that tumors, which can be displaced and deformed by respiratory and cardiac motions, are more accurately targeted. This prevents unnecessary amounts of radiation from being administered to nontreatment areas—that is, the adjacent healthy tissue and organs that is usually included in the radiotherapy margin. The reduced involvement of healthy tissue could potentially minimize the probability or severity of side effects.

The developers programmed the robotic system with proposed algorithms to predict tumor motion and to compensate for errors caused by delay in system response. The system is automatically adjusted so that the tumor’s position remains stationary during treatment. Irradiated planning target volume (PTV) was 20% to 30% less for medium-size tumors and more than 50% less for small tumors when active tracking was applied and tumor motion range was up to 1.5 cm. For tumor motion range up to 2.5 cm, irradiated PTV was two times smaller when tracking was applied.

“The proposed robotic system needs 2 seconds to start tracking with the high precision level,” explained Dr. Buzurovic in describing the study, which appears in Physics in Medicine & Biology (2011;56[5]:1299-1318). “The tracking error was less than 0.5 mm for regular breathing patterns and less than 1 mm for highly irregular respiration.”