A method of implementing inhomogeneity corrections in radiotherapy. Treatment planning: comparison with experiment and Monte Carlo calculations

Computerised tomography can provide the necessary anatomical and physical data required for treatment planning purposes, including inhomogeneity corrections. A correction technique is described which uses the effective radiological thickness method together with a calibration of the CT-scanner in terms of electrons/cc. For homogeneous and inhomogeneous slab-type phantoms central axis depth-dose curves have been measured, and are compared with these calculated values and also those obtained by Monte Carlo techniques. Reasonable agreement exists well outside inhomogeneities, but a more sophisticated method is required within and close to the inhomogeneity. A tissue-air-ratio power law method is proposed which agrees well with experiment