ABSTRACT
Beam's eye view imaging has been applied to guidance of radiation therapy for decades and provides arguably the most useful view possible, that is, that of the tumor volume relative to the collimation of the treatment beam. Aside from atomic number, various other physical properties are important in selecting an appropriate target material. Although aluminum has been shown to have advantages with regard to contrast-to-noise ratio (CNR) improvement, it has a comparatively low melting point. Tsechanksi suggested that it may be preferable to use a thin target, that is, with a thickness less than the continual slowing down approximation range of the electron in the target medium. Typical clinical therapy beams contain almost no photons in the diagnostic energy range. Although the main rationale for low-Z targets beamlines is improved Contrast-to-Noise Ratio (CNR), several studies of spatial resolution have been conducted. Previous investigations have demonstrated the value of lowering the incident electron beam energy in increasing CNR per unit dose.
