Focused ultrasound is a new technology that is being used to treat certain kinds of cancers in children, like cancer in the bones and brain. The approach is similar to the ultrasound that mothers receive to view their babies during pregnancy, only more powerful. The increased power of the ultrasound allows it to be used to treat the cancer, rather than just for imaging. How does focused ultrasound work? What type of childhood cancers can it treat? What are the advantages and disadvantages of focused ultrasound compared to more traditional treatments like surgery, chemotherapy, and radiation therapy?