This property of protons, which has been called the " depth charge effect " by analogy to the explosives 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.
22.
Proximity effects ( due to electron scattering ) can be addressed by solving the inverse problem and calculating the exposure function " E ( x, y ) " that leads to a dose distribution as close as possible to the desired dose " D ( x, y ) " when convolved by the scattering distribution point spread function " PSF ( x, y ) ".
