energy is deposited within a limited distance, so tissue beyond this range (and to some extent also tissue inside this range) is spared from the effects of radiation. This property of protons, which has been called the "depth charge effect" by analogy to the explosive weapons used in anti-submarine warfare, allows for conformal dose distributions to be created around even very irregularly shaped targets, and for higher doses to targets surrounded or backstopped by radiation-sensitive structures such as the optic chiasm or brainstem. The development of "intensity modulated" techniques allowed similar conformities to be attained using linear accelerator radiosurgery. there was no evidence that proton therapy is better than any other types of treatment in most cases, except for a "handful of rare pediatric cancers". Critics, responding to the increasing number of very expensive PBT installations, spoke of a "medical arms race" and "crazy medicine and unsustainable public policy". References External links Treating Tumors that Move with Respiration Book on Radiosurgery to moving targets (July 2007) Shaped Beam Radiosurgery Book on LINAC-based radiosurgery using multileaf collimation (March 2011) Neurology procedures Radiobiology Radiation therapy procedures Neurosurgery